GENERAL SUGGESTIONS TO THE STUDENT 
 
 1. Solids like match sticks, bits of glass or metal should never 
 be thrown into the sinks. They clog the plumbing and cause great 
 annoyance and damage. Put them in the waste jars provided for" 
 the purpose. 
 
 2. Paper is out of place in the sinks. It is dangerous to put it 
 in the waste jars, where it often takes fire. The proper place for it 
 is the waste-paper basket. 
 
 3. The student will find that he has a strong tendency to take 
 too much of the various substances required in his work. This 
 tendency must be overcome before any real progress can be made. 
 The quantity needed is stated in each study. To take more means 
 wast^ of material and of time. 
 
 4. Never pour water into concentrated sulphuric acid. In diluting 
 sulphuric acid, the acid should be added to the water in a thin stream, 
 with Constant stirring. 
 
 5. When it is necessary to mix ammonia with an acid, both should 
 be d' luted before mixing. Explosive interaction occurs when con- 
 centrated ammonia is mixed with concentrated acids. 
 
 6. Before using a vessel, make sure that it is dean. Experiments 
 in dirty vessels are not worth making, for the results are only mis- 
 leading. 
 
 7. | Learn to regulate the height of your burner flame. For heating 
 test tibes and beakers, a small flame is better than a large one. 
 
 8. (Take at least five minutes at the end of each laboratory period 
 to clean up your glassware and put your working place in order. 
 
 THE NOTEBOOK 
 
 9. Neat, full, and accurate notes are necessary, especially to those 
 of you who expect to obtain credit for your chemical work in college, 
 university, or before any examining board. Do not copy the directions 
 from ihe, manual. State, in your own way, the object of each experi- 
 ment, the method and apparatus, the results, and your conclusions. 
 Frequently, a simple line drawing, similar to those in the textbook, 
 will make your description easier to understand. The notebook should 
 be provided with an index. 
 
GIFT OF 
 
 
TWENTIETH CENTURY TEXT-BOOKS 
 
 LABORATOKY STUDIES 
 IN CHEMISTRY 
 
 BY 
 ROBERT H. BRADBURY, A.M., PH.D. 
 
 HEAD OF THE DEPARTMENT OF SCIENCE IN THE 
 SOUTHERN HIGH SCHOOL, PHILADELPHIA 
 
 D. APPLETON AND COMPANY 
 
 NEW YORK CHICAGO 
 
TWENTIETH CENTURY TEXT-BOOKS 
 
COPYRIGHT, 1912, 
 BY D. APPLETON AND COMPANY. 
 
PREFACE 
 
 Briefly stated, the main features of this laboratory manual 
 are as follows : 
 
 1. It covers thoroughly the various syllabi which teachers 
 preparing students for college have to consider. 
 
 2. Each exercise, including the writing of the notes, can be 
 finished within ninety minutes. 
 
 3. The apparatus required is simple and inexpensive, and 
 due regard has been given to the prices of the chemicals. 
 Expensive substances are employed at times, but only in very 
 small quantities. 
 
 4. The fact has not been overlooked that the teacher of 
 science usually carries as many hours on the roster as the 
 teacher who has no apparatus or materials to arrange. I have 
 tried to simplify the manual labor required of the teacher, 
 without reducing the efficiency of the work. 
 
 5. The experienced teacher will at once perceive that the 
 practical details of the experiments have been worked out 
 with unusual care. It has, in fact, taken me many years to 
 get these laboratory studies into the shape in which they are 
 here presented, and I have refrained from publishing them 
 until I had made sure that they wefe as perfect as the pains- 
 taking labor of my students and myself could make them. I 
 shall be very grateful indeed for any suggestions as to further 
 improvements from other teachers. 
 
 It is, of course, as impossible as it is undesirable to frame a 
 set of directions which shall be a substitute for the teacher. 
 What I have tried to do is merely to save the appalling waste 
 of energy involved in the constant repetition of details such 
 
 iii 
 
 264202 
 
iv PREFACE 
 
 as quantity needed, vessel to use, height of flame, dilution, etc. 
 To supply this sort of information is precisely the function of 
 the laboratory manual. 
 
 6. It is not at all difficult, at present, to put together a set 
 of exercises which will occupy the laboratory .time of the 
 beginner for a year in a pleasant and orderly way. It is 
 less easy to make sure that each experiment is significant and 
 worth while, that it adds something to the logical develop- 
 ment of the student's ideas and to his appreciation of the 
 general points of view of the science. I confess that much 
 that is offered under the caption of laboratory work seems 
 to me hardly worth the time it takes. The student who 
 comes to the laboratory might otherwise be doing serious 
 work of permanent value in languages or in mathematics. 
 His time should not be wasted with purely spectacular and 
 pyrotechnic experiments, or with so-called quantitative studies, 
 
 like the heating of magnesium powder in which even the 
 most finished experimental technique must fail to secure rea- 
 sonably exact results. 
 
 One of the chief devices I have employed in attempting to 
 give greater educational value to the work is classification. 
 For instance, the facts which relate to some central topic such 
 as the action of soluble hydroxides on salt solutions, or the 
 effect of heat upon carbonates, are not scattered through the 
 book in a wholly aimless way : they are organized into a 
 compact laboratory exercise which serves, once for all, to make 
 the matter clear. Examples of this general principle of ar- 
 rangement will be found in the exercises numbered 14, 22, 
 31, 37, 58, 59, and others. 
 
 7. Probably all teachers agree, nowadays, that some of the 
 work should be quantitative. The quantitative experiments 
 in this book have been worked out with the utmost care. 
 Since I have, in my notebooks, upwards of a thousand re- 
 sults for each of them, I may fairly say that they are quite 
 within the capacity of high school students, who, in fact, 
 
PREFACE V 
 
 work them out with enthusiastic interest. Naturally, the 
 effect in improving the manipulative technique of the students 
 is very marked. Far more important is the reality which is 
 given to their conceptions of the foundations of the science. 
 It is almost impossible to teach quantitative ideas without 
 quantitative experimentation to give substance to the teaching. 
 
 A balance sensitive to a milligram can now be bought for 
 about ten dollars. Small weights, which may be lost from 
 the set, can be easily and cheaply replaced by cut lengths of 
 No. 36 German silver wire, B. & S. gauge, one centimeter of 
 which weighs almost exactly one milligram. The rest of the 
 apparatus required' is of the simplest description. 
 
 8. The literature of the elementary laboratory is now quite 
 extensive, and I have tried to make a careful survey of it. 
 Among the books which have been most helpful are Stoddard's 
 Quantitative Experiments in General Chemistry, Karl Scheid's 
 Praktischer Unterriclit in CJiemie, Ohmann's Chemie, and the 
 Laboratory Manual of Alexander Smith. 
 
 The quantity of material required in the experiments is, in 
 all cases, stated in a precise numerical way. These statements 
 are intended simply to give the student a good approximate 
 idea of the amount he should take. It is only in the quantita- 
 tive exercises that the quantity stated should be accurately 
 weighed or measured. The apparatus and materials needed 
 are stated at the beginning of each exercise. Supplies always 
 on the student's table, such as the burner, the stand, and the 
 ordinary acids, are omitted. 
 
 A lead disk about 6x2 cm., pierced radially and axially is 
 convenient for collecting gases over water. It is used in an 
 agate pan, the bottle of water being inverted over the central 
 perforation. The disk also has been omitted from the lists of 
 necessary supplies, since there are many other devices which 
 may serve the purpose equally well. 
 
 It may not be amiss to call the attention of teachers to the 
 use of potassium permanganate, instead of manganese dioxide, 
 
vi PREFACE 
 
 for generating chlorine, and of formic acid, instead of oxalic 
 acid, in the preparation of carbon monoxide. In both cases, 
 the older methods have been obsolete among chemists for 
 some years, and one cannot help wondering at the misplaced 
 conservatism which causes their continued republication in the 
 newer elementary texts. 
 
 It is not improbable that chemists who are not engaged in 
 secondary teaching may be surprised at the care which has 
 been taken to exclude complex and expensive apparatus. Let 
 me add, therefore, that the secondary school teacher handles 
 sections of thirty or more without laboratory assistance and 
 without time for preparation, that he must finish his exercise 
 in a definite time, which is usually not greater than ninety 
 minutes, and that his students have had no opportunity to 
 acquire manipulative skill. When these conditions are gen- 
 erally understood, a certain amount of energy, which is now 
 wasted in rather futile criticism of secondary aims and 
 methods, will be expended in some more useful way. In fact, 
 to do the best that can be done under these circumstances 
 forms a difficult problem, which is quite different from the 
 problem of the college or university instructor. To offer, in 
 a small way, some help toward the solution of the problem of 
 elementary teaching is the object of the present book. 
 
 Professor Alfred L. Carey of the Southern High School has 
 assisted me with the reading of the proof. The illustrations 
 are from original drawings made by my wife. 
 
 ROBERT H. BRADBURY. 
 
CONTENTS 
 
 1. Glass Rod. Tubing 1 
 
 2. Capacity of Laboratory Vessels 3 
 
 3. Density of Liquids 4 
 
 4. Density of Sulphur, Copper Sulphate, and Marble . . 5 
 
 5. Sulphur (J 
 
 6. Galenite. The Use of the Blowpipe 8 
 
 7. Pyrite 9 
 
 8. Chalcopyrite {Copper Pyrite) 10 
 
 9. Artificial Sulphur-Compounds 11 
 
 10. Synthesis of Copper Sulphide (Cuprous) (Quantitative") . 13 
 
 11. The Cyanide Process for extracting Gold from its Ores . 15 
 
 12. The Effect of Heat on Wood and Soft Coal .... 16 
 
 13. Wood Charcoal and Animal Charcoal (Boneblack) . . 16 
 
 14. Heating Metals in the Air 17 
 
 15. The Combustion of Phosphorus in an Enclosed Volume of 
 
 Air 18 
 
 16. The Percentage of Oxygen in Air 19 
 
 17. Chemical Nitrogen 21 
 
 18. Oxygen (Preliminary Experiments) ..... 22 
 
 19. Oxygen (Preparation) 23 
 
 20. Carbon Dioxide (Preliminary Experiments) .... 25 
 
 21. Preparation of Carbon Dioxide 27 
 
 22. The Action of Carbon on Oxides of Metals .... 28 
 
 23. Arsenolite (Arsenious Oxide} and Arsenic .... 29 
 
 24. Carbon Monoxide 30 
 
 25. The Atomic Weight of Tin (Quantitative) .... 32 
 
 26. The Distillation of Water 33 
 
 27. Crystallization 34 
 
 28. Preparation of Crystallized Sodium Carbonate ... 35 
 
 29. Solution (1) 35 
 
 30. Solution (2) 37 
 
 31. Water of Crystallization 39 
 
 vii 
 
viii CONTENTS 
 
 EXERCISE PAGE 
 
 32. Water of Crystallization (Quantitative) . . . .40 
 
 33. The Action of Zinc and Iron on Water . . . .41 
 
 34. The Interaction of Sodium and Water 43 
 
 35. The Interaction of Calcium and Water 44 
 
 36. Hydrogen 45 
 
 37. Flame 47 
 
 38. Hydrogen Sulphide 50 
 
 39. Ammonia .......... 51 
 
 40. Neutralization of Ammonium Hydroxide by Acids (Ammo- 
 
 nium Salts) 53 
 
 41. Methane 55 
 
 42. Carbohydrates 56 
 
 43. Acetic Acid, Wood Alcohol, Acetylene 57 
 
 44. Chlorine 59 
 
 45. The Action of Sulphuric Acid on Chlorides .... 62 
 
 46. The Action of Sulphuric Acid on Salt 63 
 
 47. The Action of Hydrochloric Acid on Sodium Hydrogen 
 
 Sulphate 64 
 
 48. The Action of Hydrochloric Acid upon Metals ... 64 
 
 49. The Action of Hydrochloric Acid upon Oxides ... 66 
 
 50. Flame Tests 67 
 
 51. Preparation of Sodium Hydrogen Carbonate and Sodium 
 
 Carbonate (Solvay Process) 68 
 
 52. Hydrogen Fluoride . . . . . . . .69 
 
 53. Bromine 71 
 
 54. Iodine 73 
 
 55. Silver Compounds of the Halogens (The Replacement of One 
 
 Halogen by Another) 75 
 
 56. Neutralization (1) 77 
 
 57. Neutralization (2) (Quantitative) 78 
 
 58. The Action of Bases on Salts 80 
 
 59. The Action of a Metal on a Solution of a Salt of Another 
 
 Metal 82 
 
 60. Ionized and Un-ionized Solutions ...... 84 
 
 61. Hydrolysis 85 
 
 62. Separation of Lead, Silver, and Mercury .... 87 
 
 63. The Bead Tests 89 
 
 64. Dyeing 92 
 
 65. Nitric Acid, Aqua Regia . 94 
 
CONTENTS ix 
 
 EXERCISE PAGE 
 
 66. Potassium Nitrate 96 
 
 67. Preparation of Sodium Nitrite 97 
 
 68. Nitric Oxide 98 
 
 69. Nitrous Oxide 99 
 
 70. Phosphate Fertilizers 101 
 
 71. Potassium Chromate and Potassium Bichromate . . . 102 
 
 72. Ammonium Dichromate 104 
 
 73. The Percentage of Chromium in Ammonium Dichromate 
 
 (Quantitative) 105 
 
 74. The Percentage of Iron in Ferrous Ammonium Sulphate 
 
 (Quantitative) ......... 106 
 
 75. Determination of the Percentage of Chlorine in Sodium 
 
 Chloride (Quantitative) 107 
 
 76. Analysis of a Silver Coin (Quantitative) .... 109 
 
 77. The Atomic Weight of Copper by reducing Cupric Oxide 
 
 (Quantitative) 110 
 
 78. Percentage of Copper in Copper Sulphate Crystals (Quanti- 
 
 tative) 112 
 
 79. The Atomic Weight of Copper by Oxidizing Reduced Copper 
 
 (Quantitative) 112 
 
 80. The Atomic Weight of Sulphur (Quantitative) . . .113 
 
 81. The Formula of Zinc Chloride (Quantitative) . . .114 
 
 82. Percentage of Oxygen in Potassium Chlorate (Quantitative) 115 
 
 83. The Effect of Heat and of Acids on Carbonates . . .116 
 
 84. The Effect of Heat on a Carbonate (Quantitative) . . 118 
 
 85. Boric Acid and Borax 119 
 
 86. The Atomic Weight of Magnesium 120 
 
 87. The Production of a Double Salt 123 
 
 APPARATUS AND SPECIAL MATERIALS 125 
 
 CHEMICALS 127 
 
 MINERALS .... 129 
 
LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 1 
 
 GLASS ROD. TUBING 
 
 Apparatus. Triangular file. Bunsen burner. Wing-top.- 
 Materials. Glass rod and tubing. Sugar. 
 
 Method. Glass rod or tubing can be cut by making a notch with 
 a file and bending away from the notch. 
 
 A. Glass rod. With a triangular file, make a notch on a 
 piece of thin glass rod 15 centimeters (6 in.) from the 
 end. 1 One sharp stroke of the file is sufficient. Holding the 
 rod as indicated in Fig. 1, endeavor to bend it away from the 
 notch, and it will break off 
 
 at that point. Cut off three 
 
 such pieces. Since the 
 
 ends of the rods are jagged 
 
 and inconvenient to handle, 
 
 round both ends of each 
 
 rod by holding it in the 
 
 Bunsen flame and rotating / 
 
 the rod gently. Support F IG> i 
 
 the rods by the middle on , 
 
 your test-tube rack until they cool. (Hot glassware or hot 
 
 apparatus of any kind must never be laid on the desk or put 
 
 away under it.) 
 
 B. Glass tubing. Cut, just as you cut the glass rod, a piece 
 of glass tubing 20 cm. (8 in.) in length. Hold the middle of 
 the piece of glass tubing in the flame, turning it slowly, and 
 
 1 Rod not over 3 millimeters in diameter is best. The use of thick 
 stirring-rods is a frequent cause of breakage of beakers. 
 
 1 
 
LABORATORY STUDIES IN CHEMISTRY 
 
 when it becomes red-hot, gently and slowly draw the two por- 
 tions apart. Do not twist the tubes. The pull must be straight. 
 Let the two tubes cool and use them to study the effect of 
 heat upon a fragment of wood (match-stick) and a little 
 sugar. 
 
 Bending glass tubing. For bending, fit a wing-top on the 
 Bunsen burner. Hold the tube so that the flame heats as long 
 a portion as possible, and rotate it so that it is evenly heated. 
 When sufficiently hot, remove it from the flame and make the 
 bend. 
 
 In this way, bend a glass tube 15 cm. (6 in.) long into an 
 acute angle (Fig. 2). Cut a piece of glass tubing about 25 cm. 
 
 (10 in.) long and bend it 
 
 twice at right angles (Fig. 3). 
 This must be done so that, 
 when the double bend is laid 
 upon the table, every part of 
 FIG. 3. it will touch the surface of 
 
 the latter, or, in other words, 
 
 the two limbs must be in the same plane. Round the sharp 
 ends of the bent tube by holding them a short time in the 
 flame not long enough to cause them to collapse. 
 
 FIG. 2. 
 
CAPACITY OF LABORATORY VESSELS 3 
 
 EXERCISE 2 
 
 CAPACITY OF LABORATORY VESSELS 
 
 Apparatus. A 100 cubic centimeter cylinder, graduated in cubic 
 centimeters. (Use the expression c.c. for cubic centimeter.) Large 
 and small test tubes. Evaporating dish. Bottle. Beaker. 
 
 Materials. Rubber bands. 
 
 Method. The vessel is filled with water, which is then poured into 
 a graduated cylinder. 
 
 Measure 5 c.c. of water in the graduated cylinder and pour it 
 into the small test tube. This tube is 6 in. long by f in. diam- 
 eter. In metric measure it is 15 cm. by 1.8 cm. Mark the up- 
 per level of the water by a rubber band slipped around the 
 tube. See that the upper edge of the band is at the lower 
 meniscus of the water (Fig. 4). Memorize the appearance of 
 5 c.c. of water so that when you are asked to take that quantity 
 of a liquid in an. experiment you may have a definite idea of 
 how much is meant. Add another 5 c.c. of water, 
 mark the upper level, and memorize the appearance of 
 10 c.c. of liquid. Now fill the tube completely and 
 pour the water into the empty measuring cylinder. 
 
 The length of the large test tube is 8 in. (about 
 20 cm.) and its diameter 1 in. (2.5 cm.). Repeat the 
 work, using the large test tube. Where the capacity FIG. 4. 
 of a vessel is greater than 100 c.c., determine it by 
 first pouring exactly 100 c.c. of water in it and then measuring 
 the additional water required to fill it. 
 
 Place first 25 c.c. and then 50 c.c. of* water in the beaker, 
 marking the levels. Then get the total capacity. Get the 
 total capacity of your evaporating dish and one of your bottles. 
 Record the results. 
 
4 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 3 
 
 DENSITY OF LIQUIDS 
 
 Apparatus. Trip scales and weights. 100 c.c. measuring cylinder 
 graduated in c.c. 
 
 Materials. Water. 95 per cent grain alcohol. Saturated salt 
 water. 
 
 Method. A measured volume of the liquid is weighed. 
 
 Clean the cylinder if necessary and dry it carefully with a 
 towel. Weigh it as accurately as possible and record the 
 weight in your notebook. Count the weights at least twice. 
 
 Remove the cylinder from the scales and place in it 20 c.c. 
 of water. Read from the bottom of the meniscus (Fig. 5). 
 
 Weigh the cylinder with the water. Get the weight of the 
 water by difference, and calculate the weight of 1 c.c. 
 
 Is the result exactly what you would expect ? If not, what 
 is the probable reason ? Bearing in mind the limits of accu- 
 racy of the scale and the cylinder, how 
 exact would the result be, provided that 
 the work was done as well as possible ? 
 Would the fourth decimal place have any 
 value ? the third ? the second ? Why ? 
 
 Dry the cylinder inside and out. You 
 need not weigh it again. Place in it 
 20 c.c. of alcohol and get the weight of 
 1 c.c. in the same way. Look up the 
 FlG 5 density of alcohol and see how close your 
 
 result is to the truth. 
 
 In the same way, determine the weight of 1 c.c. of saturated 
 brine. 1 
 
 1 The weight of 1 c.c. of saturated brine is about 1.2 grams. 
 
 20 CC 
 
SULPHUR, COPPER SULPHATE, AND MARBLE 5 
 
 EXERCISE 4 
 
 OF SULPHUR, COPPER SULPHATE, AND 
 MARBLE 
 
 Apparatus. Trip scales. Graduated cylinder. Evaporating dish. 
 
 Materials. Broken roll sulphur, free from dust. Clean marble 
 chips. Copper sulphate crystals (commonly called bluestone). Salt. 
 Alcohol. 
 
 Method. The volume of a weighed portion of the solid is obtained 
 by dropping it into water in a graduated cylinder. 
 
 Weigh or counterpoise the dish. Weigh in it exactly 10 
 grams of fragments of sulphur, free from dust. The cylinder 
 need not be weighed Place in it exactly 20 c.c. of water. 
 Incline the cylinder and carefully slide in the 10 grams of 
 sulphur The increase in volume is the volume of the sulphur. 
 Calculate the weight of 1 c.c. of sulphur. Look up the den- 
 sity of sulphur and see how nearly right you are. 
 
 Dry the wet sulphur as well as you can on paper, and put it 
 in the place designated by the instructor. Repeat the whole 
 experiment, using marble chips instead of sulphur. Dry the 
 marble as well as possible and place it in the receptacle pro- 
 vided. 
 
 Since bluestone dissolves in water, you must use some other 
 liquid. Weigh off 10 grams of bluestone, just as you did with 
 the others, but place 20 c.c. of alcohol in the dry cylinder. 
 Otherwise, the determination is made in the same way as the 
 other two, Return the alcohol to the bottle and place the 
 bluestone in the receptacle provided. 
 
 If time permits, determine the density of solid salt just as 
 you did that of bluestone, using alcohol because salt is soluble 
 in water. The salt may be thrown into the waste jar. The 
 alcohol should be returned to the bottle. 
 
6 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 5 
 SULPHUR 
 
 Apparatus. Watch glass. Agate pan. Lens. Funnel. Two 
 small dry test tubes. 
 
 Materials. Roll sulphur. Powdered roll sulphur. Flowers of 
 sulphur. Carbon disulphide. Filters. 
 
 Method. See textbook, pages 4, 5, 6, and 7. 
 
 CA UTION : Carbon disulphide is highly inflammable. It must not 
 be heated nor used near aflame. 
 
 Examine roll sulphur. Is it brittle or malleable? Dense 
 or light ? Rub a piece on the coat sleeve, and bring it near 
 very small pieces of paper. What is the result ? Does it dis- 
 solve in water ? (Use a small piece.) 
 
 Examine flowers of sulphur and record its properties. 
 
 (a) Place 0.5 c.c. of powdered roll sulphur in a dry, small 
 test tube and add 2 c.c. of carbon disulphide. Shake until 
 the sulphur dissolves. Put the liquid into a watch glass and 
 let it evaporate in a place as far from the flame as possible. 
 Examine the crystals with a lens. Make drawings of several 
 crystals. These crystals are sulphur. This form of sulphur 
 is called a-sulphur. 1 
 
 (b) Have ready a dry filter folded as though to go into a fun- 
 nel (Fig. 6) and a pan of water. Half fill a small dry test tube 
 
 FIG. 6. 
 
 with crushed roll sulphur. Hold the tube with a holder or 
 clamp and melt the sulphur by holding the tube above a small 
 flame and turning it constantly. The melted sulphur should 
 be pale amber-yellow. 
 
 1 a (Alpha) = first letter of Greek alphabet. 
 
SULPHUR 7 
 
 Hold the filter by the edge of the threefold portion and pour 
 the melted sulphur into it. Observe the crystallization of the 
 sulphur. When crystals begin to form, across the surface, pour 
 out the liquid portion into the pan of water. Unfold the filter 
 at once. Make drawings of several crystals as they appear 
 when viewed with a lens. Compare with the form of the 
 crystals obtained in (a). Is the color of the two forms of sul- 
 phur the same ? Are both forms equally brittle ? 
 
 The form of sulphur you have just made is called ^-sulphur. 1 
 Set some of the crystals aside for twenty-four hours, and ex- 
 plain the change which occurs. 
 
 Examine the sulphur which has been poured into the water. 
 Break a piece of it. Is it brittle or soft ? Does it probably 
 consist of a-sulphur or /3-sulphur? 
 Of which would it consist if you 
 kept it for a day or two ? 
 
 (c) Half fill the same test tube 
 again with crushed roll sulphur 
 and melt cautiously as before. Hold 
 the tube with a holder or take 
 the clamp from your stand. This 
 time continue heating, studying the 
 
 changes in the color and viscosity (thickness) of the liquid. 
 When the sulphur boils, light the vapor at the mouth of the 
 tube and pour the liquid slowly into the pan of water, moving 
 the tube in a circle around the funnel so as to obtain a coiled 
 thread of sulphur, rather than a lump (Fig. 7). 
 
 Examine the product. Is it hard or soft ? Is it elastic ? 
 Does it resemble the product formed when melted sulphur was 
 poured into water in (b) ? Keep some of the product from (c) 
 and describe any change which takes place in it. Is it a stable 
 form of the element ? Should you expect to find it in nature ? 
 
 1 /3 (Beta) = second letter of Greek alphabet. 
 
8 
 
 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 6 
 GALENITE. THE USE OF THE BLOWPIPE 
 
 Apparatus. Blowpipe. Wing-top burner. Funnel. Small test 
 tube. 
 
 Materials. Asbestos fiber. Prismatic blowpipe-charcoal. Gale- 
 nite (a crystallized specimen for examination and some of the 
 crushed mineral). Minerals can be crushed with a hammer upon a 
 heavy iron plate. A cylinder of tin or cardboard, about 8 cm. high x 
 15 cm. in diameter, open at both ends, is convenient to prevent the 
 mineral from flying sideways. 
 
 Method. See textbook, page 10. 
 
 (a) Wash off the mouthpiece of the blowpipe. Close the 
 holes at the base of the burner and fit on the wing-top. Use 
 the luminous flame turned down to a height of 2.5 cm. (1 in.). 
 Take the blowpipe with the right hand about 
 7.5 cm. (3 in.) above the bend. Rest the 
 right elbow on the table and put the tip of 
 the blowpipe about halfway through the 
 flame, the broad surface of which should be 
 toward you. Blow gently. Keep the cheeks* 
 somewhat distended. Use them as a reser- 
 voir of air which is replenished when neces- 
 sary from the lungs. The natural tendency 
 of the cheeks to collapse will give sufficient 
 blast. The flame should be blue, noiseless, 
 and steady. A flickering or noisy flame in- 
 dicates that the blast is too strong. 
 
 (&) Make, with your knife, a depression 
 about 3 mm. (0.1 in.) deep by 1 cm. (0.4 in.) 
 diameter, near one end of the charcoal. Place a 2 mm. (0.08 
 in.) fragment of galenite in this depression and direct the flame 
 upon it, holding the charcoal sloping upward away from the 
 flame at an angle of about 20. The flame should be in the 
 same plane as the long axis of the coal (Fig. 8). The hottest 
 part of the flame is just beyond the tip of the inner blue cone. 
 
 FIG. 8. 
 
PYRITE 9 
 
 When the action seems complete, let cool, remove the product 
 from the charcoal, and examine. Is it brittle, like galenite ? 
 What is it ? 
 
 CAUTION ': A void inhaling the red poisonous gas which escapes when 
 nitric acid acts upon metals or other substances. 
 
 (c) 1 Place 1 c.c. of powdered galenite in a small test tube and 
 add 2 c.c. of concentrated nitric acid. Warm gently with a 
 small flame, not touching the tube, until the mineral disappears. 
 Half fill the tube with water. Plug up the angle of a funnel 
 with asbestos and pour the liquid upon it. With the aid of 
 more water, get all the material in the tube upon the asbestos. 
 Wash three times with water to remove nitric acid. What does 
 the residue appear to be ? Let it dry as long as time will per- 
 mit, place it on charcoal, and heat with the blowpipe flame. 
 When it begins to burn, stop heating and notice the odor. Does 
 this confirm your guess as to its nature ? 
 
 EXERCISE 7 
 
 PYRITE 
 
 Apparatus. Blowpipe. Wing-top burner. Small test tube. Fun- 
 nel. Magnet. 
 
 Materials. Pyrite (a well-crystallized specimen for examination 
 and some of the crushed mineral for class use). Asbestos. Prismatic 
 blowpipe-charcoal. Glass tubing. 
 
 Method. See textbook, page 13. 
 
 (a) Place a 2 mm. (0.08 in.) fragment of pyrite in a depression 
 on charcoal and heat it in the same way as the galenite. Inter- 
 rupt the heating from time to time to notice the odor produced. 
 What element is indicated by this ? When the action seems 
 complete, break up the residue and try the action of a magnet 
 upon it. What is the result ? What metal is indicated ? 
 
 1 During the exercises upon the separation of sulphur from sulphides 
 by nitric acid, the ventilation of the laboratory may demand some 
 attention. 
 
10 LABORATORY STUDIES IN CHEMISTRY 
 
 (6) Make a tube sealed at one end (Ex. 1, B). Place in it 
 0.5 c.c. of crushed pyrite and heat it in the flame of the burner, 
 after removing the wing-top. What element do you detect? 
 If in doubt, break the tube, scrape out the substance in the upper 
 part with a little wad of asbestos, burn, and notice the odor. 
 
 (c) Treat 1 c.c. of powdered pyrite with 2 c.c. of nitric acid 
 and carry out directions of part (c) of the preceding exercise 
 with it. Avoid inhaling the gas given off when the nitric acid 
 interacts with the mineral. 
 
 What element do you detect ? What is the color of pyrite ? 
 What is the form of the crystals ? Make a drawing of a 
 crystal in your notebook. Is it hard or soft? Can you 
 scratch it with a knife ? 
 
 EXERCISE 8 
 CHALCOPYRITE 
 
 (Copper Pyrite) 
 
 Apparatus. Blowpipe. Wing -top burner. Magnet. Funnel. 
 Small test tube. Bottle. 
 
 Materials. Chalcopyrite. Pyrite. Asbestos. Prismatic blow- 
 pipe-charcoal. Iron nails. Glass tubing. 
 
 Method. See textbook, page 14. 
 
 Examine chalcopyrite and compare it with pyrite, especially 
 in color, hardness, and crystalline form. 
 
 (a) Heat a 2 mm. (0.08 in.) fragment on charcoal just as you 
 did with pyrite. Test the residue with a magnet. What is 
 the result ? 
 
 (b) Carry out directions of part (b) of Exercise 7 with chalco- 
 pyrite. What element do you detect ? 
 
 (o) Carry out directions of part (c) of the preceding exercise, 
 using 1 c.c. of powdered chalcopyrite and 2 c.c. of concentrated 
 nitric acid. Receive the liquid which passes through the 
 asbestos in a bottle. 
 
ARTIFICIAL SULPHUR-COMPOUNDS 11 
 
 Burn the solid which remains on the asbestos. What is it ? 
 
 Note the color of the liquid in the bottle. This color is 
 characteristic of copper compounds dissolved in water. Dilute 
 the liquid to at least 200 c.c., add four to five drops of concen- 
 trated sulphuric acid and place an iron nail or a piece of zinc 
 in the liquid. Describe the substance which is deposited. 
 What is it ? What three elements do you detect in chalco- 
 pyrite ? 
 
 EXERCISE 9 
 
 ARTIFICIAL SULPHUR-COMPOUNDS 
 
 Apparatus. Small, dry test tube. Trip scales. Asbestos board. 
 Lens. Medicine dropper. Mortar and pestle. Wing-top burner. 
 Blowpipe. Prismatic charcoal. 
 
 Materials. Flowers of sulphur. Iron wire. Zinc dust. Mer- 
 cury. Thin sheet copper (0.05 mm. thick). Lead foil or test lead. 
 
 Method. For copper sulphide, see textbook, page 18, section 23. 
 For lead sulphide, see textbook, page 11. For zinc sulphide, see text- 
 book, page 17. For mercury sulphide, see textbook, page 16. 
 
 (a) Cut a piece of sheet copper 4 x 12 cm. (1.6 X 5 in.). 
 Weigh it on the trip scales. Fold it parallel to the long diam- 
 eter so that the cross section forms a W (Fig. 9), and 
 satisfy yourself that it will slip easily into a small, dry 
 test tube. Make a hole near the edge of the copper so 
 that you can hang it from an iron wire. 
 
 Fill the test tube 5 cm. (2 in.) deep with flowers of 
 sulphur, clamp the tube near the mouth, and heat it 
 until the sulphur boils violently and the tube is filled 
 with the vapor. 
 
 Lower the copper into the sulphur vapor (not into the 
 liquid). Does there seem to be any evolution of heat ? 
 When the action is complete, withdraw the product FlG < ( 
 carefully and weigh it. Result ? Is the product crys- 
 talline ? (Use a lens and, if necessary, examine results ob- 
 tained by other students.) Does the product resemble copper 
 or sulphur in its properties? Proceed at once with (6). 
 
12 LABORATORY STUDIES IN CHEMISTRY 
 
 (6) Introduce into the same test tube a mass of powdered 
 lead (test lead) about equal in volume to the sulphur, or use 
 lead foil torn into small pieces, and take about six times the 
 weight of the sulphur. If you do not know this, estimate it 
 from the volume, remembering that 1 c.c. of liquid sulphur 
 weighs 2 grams. Heat. Does the product resemble galenite ? 
 Does it behave like galenite when heated on charcoal before 
 the blowpipe ? Try it. 
 
 (c) Tear a sheet of paper in halves and place half of it on 
 each side of the trip scales. The paper on the left-hand pan 
 avoids contact between the substances weighed and the scales. 
 The paper in the right-hand pan counterpoises that on the left. 
 Use this method hereafter in weighing substances with the trip 
 scales. Weigh off 2 grams of zinc dust and 1 gram of flowers 
 of sulphur. 
 
 Mix the sulphur and the zinc by putting them together and 
 pouring repeatedly from one paper to another. Transfer the 
 mixture to the asbestos board and ignite it with the burner 
 held at arm's length. The action is explosive. The product 
 is a compound of sulphur and zinc which has the same com- 
 position as zinc-blende. 
 
 CAUTION ': Remove all rings while working with mercury. Do not 
 get mercury in the sinks. 
 
 (d) Melt 3 grams of sulphur in a small, dry test tube, add 
 1 c.c. of mercury with a medicine dropper, and continue heat- 
 ing. When the action is over, allow to cool. The mass con- 
 sists of a compound of sulphur and mercury called mercuric 
 sulphide which has the same composition as the mineral cin- 
 nabar. Powder the product in a mortar and examine it. 
 
SYNTHESIS OF COPPER SULPHIDE 13 
 
 EXERCISE 10 
 
 SYNTHESIS OF COPPER SULPHIDE (CUPROUS) 
 ( Quantitative) 
 
 Apparatus. Porcelain crucible and cover. Balance. Pipe-stem 
 triangle. Meter stick (one for section). 
 
 Materials. Flowers of sulphur. Copper wire No. 30 (B. & S. 
 gauge). A meter of this wire weighs about 0.5 gram. 
 
 Method. When copper wire is heated with sulphur, copper sul- 
 phide, CuaS, is formed. Only the sulphur which combines with the 
 copper remains in the crucible. The excess of sulphur burns off. 
 See textbook, page 21. 
 
 Weigh the crucible without the cover. Coil 2 m. of the 
 wire around your pencil into a spiral, place in the crucible, and 
 weigh again. Count the weights at least three times to avoid 
 errors. 
 
 Record thus : 
 
 Crucible + copper 
 
 Crucible empty 
 
 Copper 
 
 Place about a gram (roughly weighed) of flowers of sulphur 
 in the crucible, cover, and support on the triangle. Heat gently 
 until sulphur no longer burns between crucible and cover ; then 
 heat intensely for five minutes. Take the burner in the hand 
 and make, sure that the upper part of the crucible where it joins 
 the cover is thoroughly heated. Let cool and weigh, after remov- 
 ing cover. Do not remove cover until cold. 
 
 Record thus : 
 
 Crucible + copper sulphide 
 
 Crucible + copper 
 
 Sulphur in copper sulphide 
 
 Crucible + copper sulphide 
 
 Crucible empty 
 
 Copper sulphide 
 
14 LABORATORY STUDIES IN CHEMISTRY 
 
 weight of copper x 100 = cent 
 weight copper sulphide 
 
 Calculate the percentage composition of copper sulphide thus : 
 weight of copper x 100 
 weight copper sulphide 
 
 weight sulphur x 100 = cent gu , hur 
 weight copper sulphide 
 
 How do your results agree with the composition calculated 
 from the formula Cu 2 S ? See textbook, pages 89 and 385. 
 
 Calculate the atomic weight of copper, taking that of sulphur 
 as 32. Since the formula of your sulphide is Cu 2 S, two atomic 
 weights of copper would combine with one of sulphur. 
 Hence : 
 
 Weight sulphur : weight copper : : 32 : 2 x, 
 x = atomic weight copper. 
 
 In these calculations, "weight of sulphur" means the sul- 
 phur which combines with the copper ; that is, the increase in 
 weight after heating. The quantity of sulphur taken need not 
 be accurately weighed, since the excess of sulphur is driven off 
 as vapor and burns. 
 
 In this exercise, and in all quantitative work, the student 
 should use the utmost care to avoid errors in weighing. Unless 
 the weighings are correct the work is little better than a waste 
 of time. The weights should be counted at least three times, and 
 the result recorded methodically at once. 
 
CYANIDE PROCESS FOR EXTRACTING GOLD 15 
 
 EXERCISE 11 
 
 THE CYANIDE PROCESS FOR EXTRACTING GOLD 
 FROM ITS ORES 
 
 Apparatus. 300 c.c. flask with solid rubber stopper. Tinner's 
 shears. Glass rod. 
 
 Materials. Gold leaf. Potassium cyanide. Sheet zinc. (The 
 zinc should be cleaned with emery paper before using.) 
 
 Method. See textbook, page 29. 
 
 CAUTION ' : Potassium cyanide is intensely poisonous. 
 
 (a) Place 1 gram potassium cyanide with 50 c.c water in the 
 flask, insert the stopper, and dissolve by shaking Introduce 
 about 10 sq. cm. (1.5 sq. in.) of gold leaf. The gold leaf is best 
 picked up with a wet glass rod, which is then dipped into the 
 solution in the flask. 
 
 (6) Insert the stopper and shake. At intervals remove the 
 stopper to admit oxygen, which takes part in the change. 
 Result ? What stage in the cyanide process does this illustrate ? 
 
 (c) When the gold has disappeared, add 2 sq cm. (0.3 sq. in.) 
 of freshly scraped sheet zinc, cut into small pieces, and shake 
 vigorously. Result? Remember that finely divided gold is 
 dark and without luster. What part of the cyanide process 
 does this illustrate ? 
 
16 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 12 
 THE EFFECT OF HEAT ON WOOD AND SOFT COAL 
 
 Apparatus. Dry test tubes. (Since the test tubes are to be sacri- 
 ficed, damaged ones are preferable.) 
 
 Materials. Sawdust or fragments of wood. Soft coal. Red and 
 blue litmus paper. 
 
 Method. See textbook, pages 41 and 43. 
 
 (a) Fill a dry test tube 2 cm. (0.8 in.) deep with, sawdust or 
 fragments of wood. Heat at first gently, then strongly. Test 
 gases given off as to odor, effect on both kinds of litmus paper, 
 and combustibility. What is left in the tube ? 
 
 (6) Repeat (a), using soft coal instead of sawdust. Make 
 a comparison of the results of (a) and (b) in your notes. 
 
 EXERCISE 13 
 
 WOOD CHARCOAL AND ANIMAL CHARCOAL 
 (BONEBLACK) 
 
 Apparatus. Funnel. Small test tube. 
 
 Materials. Wood charcoal. Animal charcoal. Litmus solution. 
 Lead foil (tea lead). Filters. 
 
 Method. See textbook, pages 41 and 194. 
 
 (a) Place a 1 cm. (0.4 in.) piece of wood charcoal in a test 
 tube half full of water. Is it lighter or heavier than water ? 
 Now wrap the charcoal in lead foil to sink it and punch holes 
 in the foil with a knife blade to admit the water. Put it back 
 in the test tube and boil five minutes. Remove the foil and 
 put the charcoal again in water. Result? Draw conclusions 
 with respect to the true and apparent specific gravity of char- 
 coal. 
 
 (6) Prepare a dilute solution of litmus by adding one or two 
 drops of the laboratory solution to half a test tube of water. 
 Add enough boneblack to fill the tube 2 cm. (0.8 in.) deep. Boil 
 several minutes and filter. Fold the filter paper first into a 
 
HEATING METALS IN THE AIR 17 
 
 semicircle, then into a quadrant (Fig. 6), and fit it tightly to 
 the funnel. Avoid filling the funnel above the filter. 
 
 What is the action of boneblack on litmus solution ? What 
 is boneblack used for ? 
 
 EXERCISE 14 
 
 HEATING METALS IN THE AIK 
 
 Apparatus. Pliers (one pair for class). Forceps. Porcelain cru- 
 cible. Pipe-stem triangle. Platinum foil (one piece will answer for 
 class). Tinner's shears. Meter stick. Balance. 
 
 Materials. Sheet copper (0.1 to 0.2 mm. thick). No. 30 copper 
 wire. Tin foil. Iron powder (by alcohol). Iron wire. Zinc dust. 
 Sandpaper. 
 
 Method. See textbook, page 49. 
 
 (a) Cut two pieces of copper about 10 cm. (2 in.) square. 
 Clean both pieces with sandpaper. Was the copper tarnished ? 
 Is it likely, then, that the air acts upon copper ? If so, the 
 action must be very slow, but all chemical changes are greatly 
 quickened by heat. 
 
 Hold one of the pieces of copper in forceps and heat it as 
 hot as you can without melting it. When the product of heat- 
 ing begins to peel off, let the copper cool, place a clean paper 
 on your desk, and tap the copper upon it so as to collect some 
 of the new substance. Clean the copper with sandpaper and 
 heat it again. 
 
 Would heat alone, without air, produce the change ? In 
 order to answer this question, roll up the second piece of 
 copper, squeeze the roll flat with the pliers, and fold over the 
 ends so that air will not get at the inside. Heat as hot as you 
 can, without melting, for five minutes. Let cool, and compare 
 the outside of the roll with the inside. Eesult ? 
 
 (6) l Measure roughly 5 m. (5.5 yds.) of No. 30 copper wire, 
 coil it around a lead pencil, and place in a porcelain crucible. 
 Weigh accurately and record the weight. Place the crucible 
 
 1 (&) (c), (d), (e), can be distributed to different students. 
 
18 LABORATORY STUDIES IN CHEMISTRY 
 
 on a pipe-stem triangle and heat gently. Slowly increase the 
 heat until you are using the full power of the burner. The 
 crucible should be just above the tip of the inner blue cone of 
 the flame. 
 
 After fifteen minutes, turn the flame to one half its full 
 height for a minute (to prevent sudden cooling and cracking 
 of the porcelain) and let the crucible cool. Weigh accurately. 
 Result ? What are your conclusions ? 
 
 (c) Heat a piece of tin foil 5 cm. (2 in.) square as in (6). The 
 crucible with the tin foil must be accurately weighed. Stir from 
 time to time with an iron wire, being careful not to lose any- 
 thing from the crucible. After at least fifteen minutes full 
 heat, cool gradually and weigh again. Result ? 
 
 (d) 2 c.c. of iron powder, accurately weighed with the cru- 
 cible, are heated and stirred as in (c) and then reweighed. 
 
 (e) 2 c.c. of zinc dust heated exactly as in (c). 
 
 (/) T Take a piece of platinum foil in the forceps and heat it 
 to bright redness for two minutes. Platinum belongs to the 
 class of " noble metals." Let the platinum cool and notice the 
 absence of alteration. 
 
 EXERCISE 15 
 
 THE COMBUSTION OF PHOSPHORUS IN AN 
 ENCLOSED VOLUME OF AIR 
 
 Apparatus. Bottle. Agate pan. Graduated cylinder. Small, 
 flat cork. Glass plate 8 cm. square. 
 
 Materials. Red phosphorus. Asbestos paper. Wooden splints. 
 Pins. 
 
 Method. Phosphorus combines with the oxygen of the air and 
 does not affect the nitrogen. 
 
 Pin a piece of asbestos paper to the cork, place on it 
 1 c.c. of red phosphorus, and float it on water in the agate pan. 
 Ignite the phosphorus and at once invert over it the bottle. 
 
 1 For all students. 
 
THE PERCENTAGE OF OXYGEN IN AIR 
 
 19 
 
 Wait until the white cloud of phosphorus pentoxide, P 2 5 , has 
 disappeared. Slip a glass plate tightly under the mouth of 
 the bottle and remove it from the pan without allowing any 
 air to enter. Set it upright upon the desk. Light a splint, 
 remove the glass plate, and instantly plunge the burning wood 
 into the gas. Pour the water into a graduated cylinder and 
 measure its volume. Get the total volume of the bottle. Cal- 
 culate the percentage of oxygen in the air. 
 
 How does the result compare with the accurate figure? 
 (See textbook, page 57.) Should you expect an exact result 
 or merely a rough approximation ? What are the chief causes 
 of error in the method ? Should you expect the result to be 
 low or high ? Why ? 
 
 EXERCISE 16 
 THE PERCENTAGE OF OXYGEN IN AIR 
 
 Apparatus is shown in the figure (No. 10). A large test tube is 
 closed by a doubly perforated rubber stopper (No. 5). One hole is 
 tightly plugged with a bit of thick glass rod, 
 the ends of which have been rounded in the 
 flame. Through the other hole passes a tightly 
 fitting short piece of glass tubing which reaches 
 1 cm. (0.4 in.) below the stopper. The lower 
 end of this tube has been held in the flame until 
 it has melted sufficiently to reduce the bore 
 about one half. A rubber tube 15 cm. (6 in.) 
 long connects the upper end of this tube with 
 a funnel as shown in the figure. The rubber 
 tube is provided with a Mohr pinchcock. 
 
 Materials. Dissolve 200 grams of potassium 
 hydroxide in 1 liter of water. Add 20 grams 
 of pyrogallol, which will dissolve instantly in 
 the liquid. This solution will serve for at least 
 20 students. It should be kept in a well- 
 stoppered bottle. Or, dissolve 10 grams potassium hydroxide in 50 
 c.c. water, add 1 gram pyrogallol, stir, and use at once. Rubber bands. 
 
20 LABORATORY STUDIES IN CHEMISTRY 
 
 Method. A solution of pyrogallol absorbs the oxygen from a meas- 
 ured volume of air, leaving the nitrogen. 
 
 CA UTION : Potassium hydroxide must not be touched with the fingers 
 nor weighed on the bare balance pan. 
 
 Remove the test tube and take out the glass rod from the 
 stopper. Pour about 40 c.c. of the solution just mentioned into 
 the funnel. Open the pinchcock until the liquid has filled 
 the rubber tube and the glass tube completely. If this is care- 
 fully done, scarcely any of the liquid need be allowed to run 
 out. The solution stains the flesh and should not be allowed 
 to touch the hands. It spoils on exposure to air, and the ex- 
 periment should be finished as promptly as possible after the 
 solution is put into the funnel. 
 
 Now insert the stopper tightly, and then plug up the second 
 hole of the stopper with the piece of glass rod. Open the 
 pinchcock. A little of the solution will be forced into the 
 test tube by the pressure of the liquid above, and, as the oxygen 
 disappears, more will enter. When the liquid stops flowing 
 in, close the pinchcock and turn the test tube upside down 
 several times to absorb the last traces of oxygen. In doing 
 this, do not take hold of the tube with the hand, since this 
 would warm the gas and give a false result. Use a paper 
 holder or a clamp. Open the pinchcock and bring the inverted 
 test tube to such a height that the level of the liquid in it and 
 the funnel are the same. Why ? 
 
 Close the pinchcock, bring the test tube back to its original 
 position, and mark the lower level of the stopper and the 
 upper level of the liquid with rubber bands. Clean the appa- 
 ratus, and with a graduated cylinder measure the capacity 
 of the tube up to the lower and upper rubber bands. The 
 first is the volume of the oxygen, the second that of the air. 
 What result do you obtain for the percentage of oxygen in the 
 air by volume ? 
 
 Calculate thus : 
 
 volume to lower band x 100 
 
 total volume to upper band 
 
 = per cent oxygen. 
 
CHEMICAL NITROGEN 
 
 21 
 
 EXERCISE 17 
 CHEMICAL NITKOGEN 
 
 Apparatus. Small flask, with rubber stopper, thistle tube, and de- 
 livery tube for collecting over water (Fig. 11). Agate pan. Wire 
 cutter. Three bottles. Wire gauze. 
 
 Materials. Sodium nitrite (commercial crystals). Ammonium 
 chloride (commercial). Iron wire No. 20. Christmas-tree candles. 
 
 Method. Nitrogen escapes when a solution containing sodium 
 nitrite and ammonium chloride is heated : 
 
 2 H 2 O 
 
 N 2 . 
 
 NaN0 2 + NH 4 C1 -+ NaCl 
 
 Put about 10 grams of ammonium chloride and the same 
 quantity of powdered sodium nitrite, NaN0 2 , in a small flask, 
 and add 80 c.c. water. Set up the apparatus as shown in Fig. 
 11. Apply a gentle heat, let the gas escape for three minutes. 
 Why? Collect three bottles of the nitrogen over water. 
 Stop heating as soon as the reaction begins, or it will become too 
 violent. If the evolution of gas threatens to become too ener- 
 getic, immerse the gen- 
 erating flask for an 
 instant only in a pan 
 of cold water, which 
 should be in readiness. 
 This will immediately 
 quiet it. 
 
 What are the physi- 
 cal properties of the 
 substance you have 
 prepared ? Does it 
 burn? Does it sup- 
 port the combustion of 
 a candle? What is 
 the most important 
 
 difference between this nitrogen and that you have obtained 
 from the air (Exercises 15 and 16) ? This nitrogen is a little 
 lighter than nitrogen obtained from air. Why ? 
 3 
 
 FIG. 11. 
 
22 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 18 
 
 OXYGEN 
 
 {Preliminary Experiments) 
 
 Apparatus. Hard glass test tube. Watch glasses about 8 cm. 
 diameter. Beaker. Small test tubes. Lens. Wire gauze. 
 
 Materials. Potassium chlorate. Manganese dioxide. Mercuric 
 oxide. Wooden splints. 
 
 Method. For mercuric oxide, see textbook, page 53. Potassium 
 chlorate, when heated, passes into oxygen and potassium chloride : 
 
 KC10 3 -> KC1 + 30. 
 
 The change takes place at a lower temperature in the presence of 
 manganese dioxide. 
 
 (a) Shake up some potassium chlorate with cold water iu a 
 test tube. Pour off a few drops of the clear solution into a 
 watch glass which serves as a cover for a beaker half full of 
 hot water. The beaker is placed on wire gauze on a ring of 
 the stand, and the water is kept hot by frequent heating to the 
 boiling-point. When crystals form, examine them with a lens 
 or a microscope. While the liquid in the watch glass is evapo- 
 rating, go on with (6). 
 
 (6) Heat 2 c.c. of potassium chlorate in a dry, clean test 
 tube. Test the escaping gas with a splint bearing a spark. 
 Result ? What is left in the tube can only be potassium chlo- 
 rate minus oxygen. Let cool, dissolve in water, and evaporate 
 a few drops to crystallization as in (a). Compare the crystals 
 with those obtained in (a), using a lens. They consist of 
 potassium chloride. 
 
 (c) Have ready 2 c.c. potassium chlorate and 2 c.c. manga- 
 nese dioxide on separate papers. Place the chlorate in a small, 
 dry test tube, clamp in a vertical position, and melt the chlorate 
 by the cautious use of a small flame. Avoid overheating. 
 Show by the spark that you have not applied a high enough 
 temperature to drive off any oxygen. 
 
OXYGEN 23 
 
 Withdraw the flame. At once throw the manganese dioxide 
 into the melted chlorate and test with the spark. Result ? The 
 manganese dioxide remains unaltered. What effect has it upon 
 the change of the potassium chlorate to potassium chloride ? 
 
 CAUTION: Rings should be removed from the hands before begin- 
 ning (of), as mercury alloys with gold and turns it white. Do not get 
 mercury into the sinks. 
 
 (d) Heat 2 c c. mercuric oxide in a hard glass test tube. 
 Use the spark test. Result ? What remains in the tube ? 
 
 EXERCISE 19 1 
 OXYGEN 
 
 (Preparation) 
 
 Apparatus. Large test tube with rubber stopper and delivery 
 tube. Four glass plates 8 cm. square. Agate pan. Iron spoon. 
 Four wide-mouthed bottles. Beaker. Wire cutter. 
 
 Materials. Iron wire. Christmas-tree candles. Picture cord. 
 Potassium chlorate. Manganese dioxide. Sulphur. Red phosphorus. 
 Sand. Asbestos paper. 
 
 Method. See textbook, pages 54, 55, and 56. 
 
 (a) Mix on paper 20 c.c. potassium chlorate with 10 c.c. man- 
 ganese dioxide. Place the mixture in the test tube. Hold the 
 tube in a horizontal position and tap it gently so as to make 
 a channel along the upper side of the mass for the escape of 
 gas otherwise explosions may occur. ^ Clamp in a horizontal 
 position and tightly insert stopper bearing delivery tube, lead- 
 ing to agate pan of water. Four inverted bottles rilled with 
 water (no air bubbles) should be ready in the pan. 
 
 Heat gently, beginning at the top. Obtain a steady evolu- 
 tion of gas. If the latter conies off violently, stop the heat 
 until it moderates. Keep the burner in motion and do not 
 heat any portion of the tube hot enough to color the flame yellow. 
 
 1 Two students working together. 
 
24 LABORATORY STUDIES IN CHEMISTRY 
 
 From time to time, take out water with a beaker from the pan 
 so as to keep the latter about half full. Bottles full of oxygen 
 can be covered under water with a glass plate 
 and set in the desk right side up until used. 
 
 (6) In the following experiments, the bottles 
 should be allowed to stand on the desk and the 
 glass plate slipped aside just enough to allow 
 the admission of the burning substance, which 
 should be held near, but not touching, the 
 bottom. The flame should not be allowed to 
 come in contact with the bottle, as it will crack 
 the glass. 
 
 Fasten a candle in a wire as in Fig. 12, light 
 and place in oxygen. Keep the flame upper- 
 most. Result ? Keep the bottle covered. How does the 
 flame differ from that of a candle burning in air, and why? 
 Why is it finally extinguished ? Does the candle seem to 
 burn more or less rapidly in oxygen than in air ? If it burned 
 at the same rate, how much longer would it burn in a closed 
 bottle of oxygen than in the same bottle filled with air ? How 
 much greater is the concentration of oxygen in pure oxygen 
 than in air under the same pressure ? Follow the same line of 
 thought in interpreting the other three combustions. 
 
 (c) Line a clean iron spoon with asbestos paper, fill it with 
 red phosphorus, ignite, and place in oxygen as in (6). Does the 
 product seem to be a solid or a gas ? Name it. Clean the 
 spoon for the next experiment by heating it to redness for two 
 minutes. It should be held nearly vertical during this process, 
 so that the melted phosphorus may not run out. Then let it 
 cool completely and reline it for the next experiment. 
 
 (d) Fill the clean, cold spoon with sulphur, light, and place 
 in oxygen as in (c). Result? Name the product. Does it 
 seem to be a solid or a gas ? Cautiously note the odor. Re- 
 serve the sulphur in the spoon for (e). 
 
 (e) Slip aside the cover of the fourth bottle of oxygen an 
 instant and throw in 10 c.c. of sand. Replace the cover. 
 
CARBON DIOXIDE 25 
 
 Carefully melt the sulphur left in the spoon from (d) and 
 dip into it one end of a piece of iron picture cord 25 cm. (10 
 in.) long. Ignite the sulphur, and lower the picture cord into 
 a bottle of oxygen. Result? What was the object of using 
 the sand? Of using the sulphur? Do not get the sand into 
 the sinks. 
 
 EXERCISE 20 
 CAKBON DIOXIDE 
 
 (Preliminary Experiments) 
 
 Apparatus. Deflagrating spoon. Trip scales. Glass tube about 
 35 cm. (14 in.) by about 7 mm. (0.3 in.) diameter. Agate pan. Glass 
 plate. Three wide-mouthed bottles of about 400 c.c. capacity. Beaker. 
 
 Materials. Limewater. Charcoal powder. Splints. Christmas- 
 tree candles. Iron wire. Asbestos fiber. Alcohol. Kerosene. 
 
 Method. See textbook, pages 98-104. 
 
 (a) Production of carbon dioxide by combustion. Fill a def- 
 lagrating spoon with powdered charcoal, heat the charcoal to 
 redness, and let it burn in a covered bottle. Test the gas with 
 lime water. 
 
 Hold a dry clean bottle over a small gas flame for a few 
 seconds. What product do you notice ? Apply the lime- 
 water test. What is the second product ? Eepeat with a 
 candle flame. With burning wood. With the flame of kero- 
 sene. Of alcohol. (The last two flames can be conveniently 
 obtained by dipping a bunch of asbestos into the correspond- 
 ing liquid, placing it on the base of your stand, and setting fire 
 to it.) 
 
 Draw conclusions regarding the existence of carbon in com- 
 bustibles and the products of their combustion. State the 
 evidence. 
 
 (b) Changes produced in air by respiration. Place some clean 
 limewater in a beaker and blow gently through it by means 
 
26 LABORATORY STUDIES IN CHEMISTRY 
 
 of a glass tube. Result ? Invert three wide-mouthed bottles 
 full of water in your agate pan and collect air in the first 
 bottle from the beginning of an expiration. Withdraw the 
 bottle from the water by means of a glass plate, slip the plate 
 aside an instant and lower into the bottle a lighted candle. 
 Does it burn as long as it would in the same volume of pure 
 air ? Why ? 
 
 In the second bottle, collect air from the end of an expira- 
 tion, using the last portions of air from the lungs. Test this 
 with a candle. Result? The result is due partly to the 
 small amount of oxygen, and partly to the large amount of 
 carbon dioxide. 
 
 Fill the lungs with air and hold the breath as long as you 
 can without discomfort. Collect the first of the expiration 
 and test it with a candle. Does the result furnish any evi- 
 dence of the diffusion of carbon dioxide upward, or of oxygen 
 downward, in the lungs ? 
 
 The body burns up about 220 grams of carbon in 24 hours, 
 almost all of which is cast out through the lungs as carbon 
 dioxide. Weigh off roughly this amount of charcoal on the 
 trip scales in order to get an idea of the quantity. Of course 
 the amount varies greatly in different people and in the same 
 person at different times. The greater the activity and the 
 lower the temperature of the surrounding air, the more active 
 the internal combustion becomes. 
 
PREPARATION OF CARBON DIOXIDE 
 
 27 
 
 EXERCISE 21 
 
 PREPARATION OF CARBON DIOXIDE 
 
 Apparatus. Gas-generating bottle. Iron spoon. Trip scales. 
 Five wide-mouthed bottles. Small test tubes. Five glass plates. 
 
 Materials. Cracked marble. Christmas-tree candles. Iron wire 
 No. 20. Magnesium ribbon. Limewater. Litmus solution. 
 
 Method. Calcium carbonate liberates carbon dioxide with acids 
 (See textbook, page 321) : 
 
 CO. 
 
 CaCO 3 + 2 IIC1 -> CaCl 2 + H 2 O 
 
 Use the apparatus shown in Fig. 13. Place the gas bottle 
 almost horizontal and slide enough broken marble into it to 
 fill it when upright to the depth of 1 cm. 
 (0.4 in.). If the lumps are too large, 
 they can be broken with a hammer on 
 an iron plate not in a mortar. Add 
 50 c.c. of water, and then hydrochloric 
 acid, slowly through the thistle tube 
 until a brisk evolution of gas is ob- 
 tained. Collect it by downward dis- 
 placement in four dry bottles. 
 
 Investigate the physical properties 
 of the gas. Has it any odor or taste ? 
 If in doubt about the last point, let 
 the gas from the generator bubble 
 through a little water in a test tube and taste the liquid. 
 Test its solubility in water by pouring water 5 cm. deep into a 
 bottle of the gas, covering tightly with the hand and shaking. 
 Suction upon the hand indicates solution of the gas. 
 
 Lower a lighted candle into a bottle of the gas. In order to 
 illustrate its high density, place a lighted candle on your desk 
 and pour carbon dioxide over it, just as you would pour water. 
 Balance a bottle on the platform scales and pour a bottle of 
 the gas into it. 
 
 A few substances will burn in the gas. Try an 8 cm. (3 in.) 
 
 FIG. 13. 
 
28 LABORATORY STUDIES IN CHEMISTRY 
 
 piece of magnesium ribbon wrapped round the stem of your 
 spoon and start burning in the air. What is the black sub- 
 stance which is obtained along with the magnesium oxide ? 
 
 Pass carbon dioxide through some limewater in a test tube 
 for some time. Notice that the calcium carbonate, which is 
 at first precipitated, finally redissolves. Calcium carbonate 
 is soluble in water containing carbon dioxide, and this solution 
 is present in many " hard waters." 
 
 Boil the liquid, and show that, when the carbon dioxide is 
 expelled, the precipitate is again obtained 
 
 Add five drops of litmus solution to 10 c.c. of water in a 
 test tube and pass carbon dioxide through the liquid. Result? 
 The presence of the water is necessary to this change. Dry 
 carbon dioxide does not affect litmus. Boil the liquid. 
 Result ? 
 
 EXERCISE 22 
 
 THE ACTION OF CARBON ON OXIDES OF 
 METALS 
 
 Apparatus. Hard glass test tube with one-hole rubber stopper and 
 delivery tube. Trip scales. Beaker. Lens. 
 
 Materials. Cupric oxide (CuO). Tin oxide (Sn0 2 ). Lead oxide 
 (PbO). Powdered charcoal. Limewater. 
 
 Method. See textbook, page 142. 
 
 (a) Mix well on paper 5 grams cupric oxide with 0.5 gram 
 powdered charcoal. Cut a piece of paper 20 x 1 cm. (8 X 0.4 in.) 
 and crease it in the middle, making a V-shaped trough. Take up 
 some of the mixture in the trough and, holding the la.tter in a 
 horizontal position, slip the tube over it. Upset the trough and 
 deposit the powder. Introduce the rest of the mixture in the 
 same way, and use this method hereafter when it is necessary 
 to get a powder into a tube without soiling the walls. 
 
 Clamp the tube in a horizontal position and insert the stop- 
 per, letting the delivery tube dip into 50 c.c. limewater in a 
 
ARSENOLITE AND ARSENIC 29 
 
 beaker (Fig. 14). Heat with a flame kept in constant motion. 
 
 Watch the limewater closely 
 
 and explain the changes which *&&* 
 
 take place in it. When the 
 
 action seems complete, remove 
 
 the limewater before the burner 
 
 Let cool completely, take out 
 
 the stopper, place the residue 
 
 in the tube on paper and ex- 
 
 amine, using a lens if necessary. 
 
 (6) Repeat, using tin oxide (5 FlG< 
 
 grams) and charcoal (1 gram). 
 
 (c) Repeat, using lead oxide (2 grams) and charcoal 
 (2 grams). Employ a gentle heat. 
 
 What is the practical importance of these results ? 
 
 If the laboratory period is short, (a), (6) and (c) can be dis- 
 tributed and the students encouraged to compare results. 
 
 EXERCISE 23 
 ARSENOLITE (Arsenious oxide) AND ARSENIC 
 
 Apparatus. Lens. Blowpipe. Evaporating dish. Small test 
 tube. 
 
 Materials. Arsenious oxide. Arsenic. Thin sheet copper. Pris- 
 matic charcoal. Powdered charcoal. Glass tubing. Filter paper. 
 
 Method. See textbook, page 293, section 387. Also page 332. 
 
 (a) Arsenious oxide. Examine the substance and compare 
 it with the element arsenic. Heat a trace of arsenious oxide in 
 a tube sealed at one end. Examine the sublimate with a lens. 
 What is the shape of the crystals ? 
 
 Dissolve about 0.1 gram of arsenious oxide by boiling it 
 gently in a test tube with dilute hydrochloric acid. Dilute the 
 liquid to 10 c.c. 
 
 Place a clean piece of sheet copper about 2 cm. square in a 
 dish, fill the dish two thirds with water, add about 1 c.c. of 
 
30 LABORATORY STUDIES IN CHEMISTRY 
 
 hydrochloric acid, and heat almost to boiling. Is there any 
 action ? Add 1 c.c. of your arsenic solution to the liquid, and 
 continue heating for ten minutes. The deposit on the copper 
 is arsenic. Remove the copper, dry it carefully with filter 
 paper, roll it up, and place it in a glass tube sealed at one end. 
 Heat it gently. Result ? Look for a sublimate with a lens. 
 
 Mix about 0.1 gram of arsenious oxide with twice its weight 
 of powdered charcoal, and heat the mixture in a glass tube 
 sealed at one end. Introduce the mixture with a paper trough. 
 The upper part of the tube must be dean. Describe and ex- 
 plain the result. 
 
 (b) Arsenic. Heat a 1 mrn. fragment of arsenic in a glass 
 tube closed at one end. Does it melt ? Does it vaporize ? 
 The two sublimates (steel-gray and black) are different allo- 
 tropic forms of arsenic. Heat a fragment of arsenic the size 
 of the head of a pin on charcoal with the blowpipe flame. The 
 visible product is arsenious oxide. Note the odor of arsenic 
 vapor. 
 
 EXERCISE 24 
 CARBON MONOXIDE 1 
 
 Apparatus. Flask, dropping* funnel, and delivery tube connected 
 as shown in cut. Agate pan. Three bottles. Wire gauze. Three 
 glass plates. 
 
 Materials. Formic acid. Sulphuric acid (concentrated) . Lime- 
 water. Iron wire. Candles. 
 
 Method. Formic acid, when heated with sulphuric acid, is con- 
 verted into carbon monoxide and water. See textbook, page 203. 
 
 Set up the apparatus as shown in cut (Fig. 15). Clamp the 
 flask firmly. The flask contains concentrated sulphuric acid 
 
 This method of making carbon monoxide is much safer and, in all 
 respects, better than the one usually given (heating oxalic acid with sul- 
 phuric acid) . Nevertheless it must be remembered that carbon monoxide 
 
CARBON MONOXIDE 
 
 31 
 
 to the depth of 1 cm, The dropping funnel is two thirds filled 
 with formic acid. Warm the sulphuric acid gently with a 
 
 FIG 15. 
 
 small flame and allow the formic acid to drop slowly into it. 
 The equation is : 
 
 CH 2 2 
 
 (Formic acid) 
 
 ->- CO ' + 
 
 Carbon monoxide 
 
 H,0. 
 
 The water is retained by the sulphuric acid. 
 
 Make, no attempt to ascertain the odor of the gas and do not 
 allow it to escape unnecessarily. Turn off the stopcock when you 
 wish to stop the evolution of gas. 
 
 Collect over water three bottles of the gas. Is the gas soluble 
 in water ? Does it burn ? Does a candle burn in an inverted 
 bottle of the gas ? Shake up some limewater in a bottle of 
 the gas. Result ? Remove the cover an instant, ignite the 
 gas, cover, and shake again. Result? What is the product 
 of the combustion ? Write the equation. 
 
32 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 25 
 THE ATOMIC WEIGHT OF TIN 
 
 (Quantitative) 
 
 Apparatus. Small test tube. Glass rod. Porcelain crucible. 
 Pipestem triangle. Balance. 
 
 Materials. Pure tin foil (free from lead 1 }. Nitric acid. 
 
 Method. Tin passes into tin dioxide when treated with nitric acid 
 and heated (see textbook, pages 298 and 299). 
 
 Weigh a porcelain crucible without the cover. Weigh in it 
 1 gram of pure tin foil. Pour upon the tin 2 c.c. of concen- 
 trated nitric acid, taking care to moisten every part of the 
 metal. Place the crucible upon the pipestem triangle on a 
 ring of your stand, warm carefully until dry, heat to bright 
 redness for ten minutes and weigh. 
 
 Calculation : 
 
 Sn + 4 HN0 3 >- Sn0 2 + 2 H 2 + 4 N0 2 . 
 
 The product in the crucible is tin dioxide, SnO 2 , and the gain in 
 weight is oxygen. Hence the atomic weight of tin is found from the 
 proportion : 
 
 Gain in weight : weight of tin : : 32 : atomic weight of tin. 
 
 1 Supply houses have a strong tendency to furnish an alloy of tin and 
 lead when pure tin foil is ordered. 
 
THE DISTILLATION OF WATER 
 
 33 
 
 EXERCISE 26 
 THE DISTILLATION OF WATER 
 
 Apparatus. Flask, with rubber stopper and delivery tube bent as 
 indicated in Figure 16. Bottle. Small test tube. Beaker. Glass 
 rod (thin). Wire gauze. 
 
 Materials. Table salt. Ammonia water. Red litmus paper. 
 Potassium permanganate. 
 
 Method. See textbook, page 112. 
 
 (a) Dissolve 3 c.c. salt in 50 c.c. water in a beaker by 
 stirring. Place the liquid in the flask and arrange as shown 
 in the figure. Boil gently 
 
 until 3 to 5 c.c. have col- 
 lected in the small test tube. 
 Taste the distilled water. 
 Is it free from salt? Ex- 
 plain. Repeat, without tast- 
 ing, with 50 c.c. of water 
 colored with a crystal of 
 potassium permanganate. 
 
 (b) In a beaker, add 3 c.c. 
 ammonia water to 50 c.c. 
 water. Note the odor of 
 the liquid and place a drop 
 of it on red litmus paper. 
 
 After cleaning the appa- 
 ratus, distill the dilute am- 
 monia in the same way as FIG. 10. 
 
 you did the salt water. Note 
 
 the odor of the distilled liquid and place a drop of it on red 
 litmus paper. Is it free from ammonia ? Explain. 
 
34 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 27 x 
 CRYSTALLIZATION 
 
 Apparatus. Wire gauze. Evaporating dish. Beaker. Graduated 
 cylinder. Mortar and pestle. Funnel. Test tubes. Trip scales. 
 
 Materials. Filters. Paper. Saltpeter (potassium nitrate). Blue- 
 stone (copper sulphate). 
 
 Method. See textbook, page 207. 
 
 (a) Measure 50 c.c. of water into a dish. Make sure that 
 the dish is dry on the outside, place it on wire gauze, and 
 heat it to boiling. Gradually add 25 grams of potassium 
 nitrate, stirring constantly with a glass rod. Heat until 
 dissolved. 
 
 Filter the liquid into a beaker, wash the dish, and dry the 
 outside. The liquid which runs through the filter is called the 
 filtrate. Return it to the dish and boil away about half of 
 the liquid. Let cool. Collect the crystals on a filter and 
 spread them out on manila paper to dry. Is there reason 
 to think that they are purer than the original material ? 
 Why? 
 
 In each of two test tubes, heat gently 5 grams of potassium 
 nitrate with 10 c.c. water until dissolved. Do not boil. Cool 
 one tube quickly by running water over it. Let the other cool 
 slowly. Compare the two crops of crystals and explain the 
 difference. 
 
 (6) If time permits, repeat the whole experiment, using 
 bluestone, which you have powdered in a clean mortar, instead 
 of saltpeter. 
 
 1 If the laboratory period is short, (a) and (&) can be assigned to dif- 
 ferent groups of students. 
 
SOLUTION 35 
 
 EXERCISE 28 
 
 PREPARATION OF CRYSTALLIZED SODIUM 
 CARBONATE 
 
 Apparatus. Evaporating dish. Graduated cylinder. Trip scales. 
 Glass rod. 
 
 Material. Anhydrous sodium carbonate (Na 2 CO 3 ). Commercial 
 calcined soda answers every purpose. 
 
 Heat 25 grams calcined soda with 60 c.c. water in a dish, 
 stirring gently. If the liquid is not clear, filter it. Let cool. 
 The crystals which form are the washing soda of the house- 
 hold (Na 2 C0 3 10 H 2 0). Compare them with calcined soda. 
 How could you reconvert them into calcined soda ? 
 
 EXERCISE 29 * 
 SOLUTION (1) 
 
 Apparatus. (For each group.) Two beakers (100 c.c.). Two 
 watch glasses suitable for covering them. Four small test tubes. 
 Two corks to fit small test tubes. Wide-mouthed bottle. Graduated 
 cylinder. Mortar and pestle. Two pieces wire gauze. 
 
 Materials. Distilled water. Powdered rosin. Copper sulphate. 
 Alcohol. 
 
 Method. See textbook, pages 207, 208 and 214. 
 
 (a) One member of the group should use distilled and the 
 other ordinary water. Carefully compare the watch glasses. 
 
 Clean a watch glass and put a few drops of distilled water 
 in it. Use the watch glass as a cover for a beaker half full of 
 water. Boil the water in the beaker gently until the water in 
 the watch glass has evaporated. Meanwhile, go on with (b) 
 and (c). If necessary, add more water to the beaker. If 
 allowed to run dry, it will break. Examine the watch glass 
 and set it aside. ,--' 
 
 1 Two students working together. 
 
36 LABORATORY STUDIES IN CHEMISTRY 
 
 With a second watch glass, test ordinary water in the same 
 way, using about the same volume. 
 
 (6) * Place 1 c.c. of powdered rosin in a test tube, cover with 
 water, and shake. Result ? 
 
 Pour off the water, cover the rosin with alcohol, and shake. 
 Result ? Keep the liquid. 
 
 Shake up some copper sulphate powder first with alcohol 
 and then with water. Explain the meaning of the terms 
 soluble, insoluble, and solution. 
 
 Pour the alcoholic solution of rosin into a bottle nearly full 
 of water. The resulting state of things is called a suspension. 
 State, in parallel columns, some differences between solutions 
 and suspensions. 
 
 (c) Since a liquid can only act at the surface of a solid, the 
 more surface exposed, the more rapidly the solid dissolves. 
 Therefore, when a solution is to be prepared quickly, the solid 
 should be powdered. 
 
 Select two crystals of bluestone about 1 cm. (0.4 in.) in diam- 
 eter and nearly equal in size. Have ready two small test tubes 
 with corks to fit them. Powder one crystal finely in a clean 
 mortar and introduce the powder into one of the test tubes. 
 Place the unpowdered crystal in the other test tube. Add, from 
 the graduated cylinder, 20 c.c. of water to each tube. Take the 
 time with a watch and record it. Insert the corks and shake 
 both tubes gently until the powdered bluestone is completely 
 dissolved. Observe the condition of the crystal and estimate 
 what fraction of it remains. Explain. 
 
 1 If the laboratory period is short, one member of the group can per- 
 form (&) while the other carries out (c). 
 
SOLUTION 37 
 
 EXERCISE 30 1 
 
 SOLUTION (2) 
 
 Apparatus (for each group). Two beakers (100 c.c.). Two watch 
 glasses suitable for covering them. Two small test tubes with corks. 
 Large test tube. Thermometer reading to 150 C. Graduated cylin- 
 der (100 c.c.). Trip scales. Two pieces wire gauze. Funnel. 
 
 Materials. Calcium sulphate (powder). Chalk (powder). Thread. 
 Calcium chloride (dry commercial). Sal ammoniac (commercial). 
 Potassium carbonate (commercial). Ether. Carbon disulphide. 
 Sodium thiosulphate (commercial "hypo"). Distilled water. Fil- 
 ters. 
 
 Method. See textbook, page 214. Also page 302, section 400. 
 
 (a) One member of the group may take calcium sulphate; the 
 other, chalk. Compare the watch glasses. 
 
 Place 1 c.c. of powdered calcium sulphate in a small test tube, 
 add 10 c.c. distilled water, cork, and shake several minutes. Let 
 settle, filter some of the liquid into a second clean test tube, and 
 test it for dissolved matter as in Exercise 29, (a). 
 
 Treat chalk in the same way. Which is the more soluble ? 
 If you had neglected to filter and evaporate, what conclusion 
 would you have formed about the solubility of both substances ? 
 Chalk is commonly spoken of as an " insoluble " substance. Is 
 there anything entirely insoluble in water ? 
 
 (6) Clamp a test tube containing 10 c.c. of water in a vertical 
 position. From a ring of the stand hang a thermometer by a 
 piece of thread so that the bulb is in the water. Weigh off 
 5 grams of dry calcium chloride on paper. 
 
 Boil the water with a small flame and take the temperature. 
 Add the calcium chloride and when the solid is all dissolved 
 take the boiling point again. Result ? 
 
 (c) One member of the group may work with sal ammoniac, and 
 the other with potassium carbonate. Carefully compare results. 
 
 Weigh 25 grams of sal ammoniac on the trip scales. Taking 
 the specific gravity as 1.5, calculate the volume of the 25 
 
 1 Two students working together. 
 4 
 
38 LABORATORY STUDIES IN CHEMISTRY 
 
 grams. Measure 80 c.c. of water in the graduated cylinder, 
 take the temperature of the water, and add the sal ammoniac. 
 Cover the cylinder tightly with the band and invert repeatedly 
 until the sal ammoniac is all dissolved. Take the temperature 
 of the solution and read the volume. 
 
 Is the volume of the solution equal to the sum of the volumes 
 of the substances it contains? What kind of a heat effect 
 occurs ? 
 
 Repeat with 25 grams of potassium carbonate (commercial 
 pearlash). In the calculation, take the specific gravity of 
 potassium carbonate as 2. 
 
 (d) One student may use ether ; the other, carbon disulphide. 
 Liquids may dissolve each other. 
 
 CA UTION: Ether and carbon disulphide must not be used near a 
 flame. Employ no heat in these experiments. 
 
 Place 3 c.c. carbon disulphide in a dry, large test tube. Add 
 3 c.c. water, one drop at a time, shaking constantly. Does 
 carbon disulphide dissolve water perceptibly ? 
 
 Now fill the tube to within 5 cm. of the top with water, cork 
 and shake. Does water dissolve carbon disulphide to any 
 large extent ? 
 
 Repeat, using 3 c.c. of ether. Is water soluble in ether ? 
 Is ether soluble in water ? 
 
 (e) Supersaturated solutions. Place a few drops of water in 
 a test tube, half fill the tube with sodium thiosulphate, called 
 " hypo " by the photographer, and heat with a small flame 
 kept in constant motion. When complete solution has occurred, 
 pour the liquid into a clean tube and cover it with paper to 
 exclude dust. Let it cool. No solid should separate. Throw 
 into the cold liquid a crystal of solid sodium thiosulphate. 
 Result ? What is a supersaturated solution ? Do you regard 
 it as a stable or an unstable state of things? Would any 
 crystal answer the purpose, if dropped into the supersaturated 
 solution in this experiment ? See textbook, pages 209 and 215. 
 
WATER OF CRYSTALLIZATION 39 
 
 EXERCISE 31 
 WATER OF CRYSTALLIZATION 
 
 Apparatus. Eight clean, dry, small test tubes. Evaporating dish. 
 
 Materials. Crystals of sodium sulphate. Copper sulphate. Zinc 
 sulphate. Potassium sulphate. Calcium sulphate (cleavage pieces of 
 gypsum). Alum. Barium chloride. Potassium nitrate. Alcohol. 
 
 Method. Water of crystallization is driven off as steam when 
 crystals containing it are gently heated. 
 
 Gently heat a few crystals of each substance in a dry, clean 
 test tube. Use a separate tube for each experiment and clamp 
 it in a horizontal position, so that the water may not run back 
 into the hot portion and break it. The flame should be kept 
 in constant motion, and the heat should not be intense enough 
 to color the flame yellow. 
 
 Classify these eight substances into (1) those which contain 
 water of crystallization' and (2) those which form anhydrous 
 (water-free) crystals. What change in structure occurs when 
 the water is driven off from the first set ? Note that anhydrous 
 crystals may contain traces of water as an impurity. 
 
 Attend especially to the striking change in the case of cop- 
 per sulphate. Dissolve most of the heated copper sulphate 
 (it is anhydrous copper sulphate, CuS0 4 ) in the smallest pos- 
 sible quantity of hot water, transfer the liquid to a dish and 
 let it cool. Explain. Throw the rest of the anhydrous 
 copper sulphate into 5 c.c. of 95 per cent alcohol. What 
 is the result ? Remember that the remaining 5 per cent of 
 the alcohol is chiefly water. Suggest a test for water based 
 upon this behavior. 
 
40 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 32 
 
 WATER OF CRYSTALLIZATION 
 (Quantitative) 
 
 Apparatus. Small porcelain crucible without cover. Pipestem 
 triangle. Balance. 
 
 Materials. Barium chloride. Magnesium sulphate. Copper sul- 
 phate. Calcium sulphate (coarsely powdered gypsum). 
 
 Method. The water is driven off by heat and its quantity obtained 
 from the loss in weight. 
 
 It is convenient to assign the different substances to different 
 groups of students. 
 
 Clean and dry the crucible and weigh it accurately. Weigh. 
 in it exactly one gram of barium chloride. Count the weights 
 at least three times to avoid errors. 
 
 Record the weights at once, thus : 
 
 Weight of crucible + barium chloride 
 
 Weight of crucible, empty 
 
 Weight of barium chloride taken . '. '. '. '. ~. 
 
 Adjust a ring of your stand to the proper height and support 
 the crucible on it by means of a pipestem triangle. Heat, at 
 first gently. After five minutes allow the bottom of the cru- 
 cible to come to & faint red heat (no hotter) and maintain it at 
 that temperature for ten minutes. Let cool and weigh when 
 cool enough to handle. 
 
 Record thus : 
 
 Weight of crucible + barium chloride 
 
 Weight of crucible + barium chloride (after heating) 
 
 Loss in weight (water) 
 
 loss in weight x 100 = per cent of water. 
 
 weight of barium chloride taken 
 
 The other three substances are treated in the same way ex- 
 cept that the temperature required is different. 
 
THE ACTION OF ZINC AND IRON ON WATER 41 
 
 Copper sulphate should be heated ten minutes with a half- 
 sized flame kept in motion. No part of the crucible should 
 glow. After weighing, the product can be dissolved in the 
 crucible in the smallest possible quantity of hot water and 
 allowed to cool. Result ? 
 
 Calcium sulphate should be heated gently for five minutes. 
 It should then receive the highest temperature the burner will 
 yield for ten minutes, after which it should be cooled gradually 
 by lowering the flame to half size for a minute before turning 
 it out, otherwise the crucible may crack. Crucibles which have 
 been highly heated should always be cooled in this way. 
 
 Magnesium sulphate should be heated in the same way as 
 calcium sulphate. 
 
 EXERCISE 33 * 
 THE ACTION OF ZINC AND IRON ON WATER 
 
 Apparatus. Small test tube with rubber stopper and delivery tube. 
 Medicine dropper. Glass plate. Bottle. Agate pan. 
 Materials. Zinc dust. Iron filings. Wooden splints. 
 Method. Heated zinc dust or iron powder liberates hydrogen 
 
 from steam. 
 
 Zn + H 2 0->ZnO + H 2 
 
 3 Fe -f 4 H 2 O -> Fe 3 O 4 + 4 H 2 . 
 
 (a) Hold the tube vertical and let fall with the medicine 
 dropper 10 drops of water to the bottom. Do not wet the sides. 
 Cut a slip of paper 20 x 1 cm. (8 x 0.4 in.) and fold it into a 
 little V-shaped trough which will slip into the tube. Holding 
 the tube in an inclined position, put in with the paper trough 
 enough zinc dust to soak up the water completely. Hold the 
 tube nearly horizontal and deposit twice the quantity of dry 
 zinc dust at D just above the wet zinc dust. Clamp the tube 
 in a horizontal position and insert the stopper with the deliv- 
 ery tube leading to a pan of water (Fig. 17). 
 
 1 (a) and (6) can be distributed to different students. 
 
42 
 
 LABORATORY STUDIES IN CHEMISTRY 
 
 Heat D, gently at first, then as intensely as you can without 
 softening the tube, then brush W with the flame so as to cause 
 steam to pass over the hot zinc. Return constantly to D with 
 the flame to keep it heated. Allow the gas to escape for the 
 first minute. Why ? Then collect it in an inverted bottle full 
 of water. When the bottle is full, slip a glass plate under it 
 
 W D 
 
 FIG. 17. 
 
 and remove it from the water. Keeping the bottle inverted, 
 thrust a burning splint up into the gas. Is the gas combusti- 
 ble ? Does it support the combustion of the wood ? 
 
 Assuming that the white substance formed in the test tube 
 is a compound of zinc and oxygen, what conclusion can you 
 draw regarding the composition of water ? If this explanation 
 is correct, what action should we expect when iron is heated 
 with steam ? 
 
 (6) Clean the test tube and repeat the experiment, using iron 
 instead of zinc. 
 
THE INTERACTION OF SODIUM AND WATER 43 
 
 EXERCISE 34 
 THE INTERACTION OF SODIUM AND WATER 
 
 Apparatus. Wide-mouthed bottle. Beaker. Watch glass. Wire 
 gauze. Small test tube. Agate pan. 
 
 Materials. Sodium. Thin lead foil (tea lead). Red and blue 
 litmus paper. Phenol phthalein solution. 
 
 Method. Sodium liberates hydrogen from water : 
 
 Na + H 2 -> NaOH + H. 
 
 Sodium must not be touched with fingers which are in the least moist 
 either with water or perspiration. Your desk must be dry when working 
 with it, and everything with which you touch it must be scrupulously dry. 
 The air acts rapidly upon sodium and it must not be exposed. Take only 
 a small piece from the bottle at a time, and immediately cork the latter. 
 The liquid over the sodium in the bottle is naphtha or kerosene, and the 
 bottle must not be opened in the vicinity of a flame. No sodium must be 
 put away under the desk nor allowed to remain lying about, since it may 
 catch Jire. None must be thrown into the waste jar, since it may ignite the 
 paper or other substances which the jar contains. Return any unused 
 portions to the bottle, or place in a vessel specially provided for that 
 purpose. 
 
 Throw a clean piece of sodium, free from crust, 2 mm. in di- 
 ameter no larger into a bottle one fourth full of water. 
 Immediately cover the bottle with a piece of paper, and wait 
 until the reaction is over before removing the cover. The action 
 usually ends with a slight explosion which may endanger the 
 eyes if the cover is removed too soon. 
 
 Describe what happens. Throw in another similar piece of 
 sodium. Feel the water in the bottle between the fingers. 
 Result ? Taste a little of it. Result ? Here, and always, 
 immediately reject the liquid tasted and rinse out the mouth with 
 water. Do not taste substances unless directed. Evaporate a 
 few drops of the liquid to dryness in a watch glass which 
 serves as a cover for a beaker half full of gently boiling water. 
 Result? Try the behavior of the liquid with red and blue 
 
44 LABORATORY STUDIES IN CHEMISTRY 
 
 litmus paper, pieces about 1 cm. (0.4 in.) square or less. Result ? 
 Allow to fall into the liquid a drop of a solution of phenol 
 phthalein. Result ? To what are these new properties of the 
 liquid due ? 
 
 Wrap a clean piece of sodium 2 mm. (0.08 in.) in diameter in 
 dry lead foil (tea lead). Punch several holes in the lead with 
 a knife blade. Invert a test tube full of water in an agate pan 
 containing water, and quickly slip the lead containing the 
 sodium under it. If necessary, use another smaller piece of 
 sodium wrapped in lead to complete the filling of the tube. 
 Take no more sodium than is directed. The use of larger 
 quantities is likely to cause explosions which may imperil the 
 sight. 
 
 What gas collects in the tube ? Is it soluble in water ? 
 Does it burn ? To what product ? Give the evidence for the 
 belief that the gas comes from the water, not from the sodium. 
 
 EXERCISE 35i 
 THE INTERACTION OF CALCIUM AND WATER 
 
 Apparatus. 25 cm. (10 in.) glass tube open at both ends. Agate 
 pan. Beaker. Small test tube. 
 
 Materials. Calcium. Red and blue litmus paper. Phenol phtha- 
 lein solution. 
 
 Method. Calcium liberates hydrogen from water : 
 Ca + 2 H 2 O -> Ca(OH) 2 + H 2 . 
 
 Throw a 2 mm. (0.08 in.) bit of calcium into 50 c.c. of water 
 in a beaker. Does gas escape ? 
 
 The liquid is lim.eivater, made in an unusual way. How 
 does it behave with red and with blue litmus paper ? Mix a 
 few drops with a drop or two of phenol phthalein solution in a 
 clean test tube. Result ? Blow through the remainder of the 
 limewater with the glass tube. Result ? 
 ._ Invert a test tube filled with water in the agate pan and 
 
 1 Alternative to Exercise 34. 
 
HYDROGEN 45 
 
 place under the mouth of the tube a bit of calcium. What 
 gas collects ? Is it combustible ? 
 
 NOTE. In spite of the most careful supervision, accidents occur 
 during laboratory work with sodium. The interaction of calcium 
 with water is perfectly safe and is in all respects a better experiment. 
 Calcium can now be purchased quite cheaply, though some little 
 inquiry may be necessary. The best way to subdivide it is to fasten 
 in a vise and chip it up with a chisel. Manual Training Schools 
 equipped with a "shaper" can cut calcium into shavings which 
 answer perfectly in the laboratory. Keep in tight-stoppered bottle. 
 
 EXERCISE 36 
 
 HYDROGEN 
 
 Apparatus. Gas-generating bottle with thistle tube and delivery 
 tube for collecting over water. Agate pan. Four wide-mouthed 
 bottles of about 400 c.c. capacity. Watch glass. Beaker. Small test 
 tubes. Glass tubing. Wire gauze. Trip scales. Four glass plates. 
 
 Materials. Mossy zinc. Wooden splints. Christmas-tree candles. 
 Iron wire. Small rubber bands. Concentrated sulphuric acid. Cop- 
 per sulphate solution. Copper oxide (black). Filters. 
 
 Method. Zinc liberates hydrogen from dilute sulphuric acid : 
 
 Zn + H 2 SO 4 ->ZnSO 4 + H 2 . 
 
 (a) 1 Place about 20 grams of mossy zinc in a gas-generating 
 bottle. The bottle must be held almost horizontal and the zinc 
 allowed to slide into it, otherwise the shock of the falling zinc 
 will break it. The bottle is provided with a doubly perforated 
 stopper carrying a thistle tube and a delivery tube, and the ap- 
 paratus is arranged for collecting the gas over water. 
 
 Insert the stopper tightly with a twisting motion, and pour 
 in through the funnel tube enough water to cover the zinc. 
 The funnel tube must dip into this water. Extinguish any 
 burner flame that may be in the neighborhood, and slowly add 
 
 1 If the laboratory period is short, it will be necessary to omit or to 
 postpone (6) and (c). 
 
46 LABORATORY STUDIES IN CHEMISTRY 
 
 concentrated sulphuric acid through the funnel tube until gas 
 is briskly evolved. Do not add too much acid. The maximum 
 should be about one fourth as much by volume as there is 
 water present. Allow the gas to escape through the water for 
 three minutes. Why ? Do not attempt at any time in the ex- 
 periment to light the gas at the exit tube. If the gas does not 
 come off freely, add a few drops of copper sulphate solution 
 through the funnel tube. 
 
 Collect the gas over water in wide-mouthed bottles of about 
 400 c,c. capacity. Determine its properties. Has it any color 
 or odor ? Is it soluble in water ? Does the method of collect- 
 ing it throw any light on this last question? In order to 
 obtain more definite information fill a test tube half full of 
 hydrogen and mark the level of the water by a rubber band. 
 Then shake the tube for a time, keeping its mouth under 
 water. Result ? Use this method hereafter in testing the 
 solubility of gases. 
 
 Will the gas support combustion? Try it by holding a 
 bottleful mouth downward and introducing a lighted candle 
 fastened on a wire. Keep the candle out of contact with the 
 walls of the cylinder so as not to wet the wick. Withdraw 
 the candle slowly. Result ? Repeat. In all work with candles, 
 support the candle on a wire so that the flame is uppermost. 
 
 Fill two bottles of the same size with the gas. Support one 
 in an inverted position in a ring of your stand, the mouth not 
 touching the table. Place the other upright. Uncover them 
 at the same moment and allow both to remain uncovered for 
 one minute. Now thrust a lighted splint into each in turn. 
 Draw conclusions. 
 
 Fill a test tube over water ^ with air and f with hydrogen. 
 Ignite the mixture. Explain the cause of this behavior. 
 Why does not the flame strike back from gas jets along the 
 mains to the gas works ? Would it be safe to supply cities 
 with a mixture, of gas and air by means of pipes ? 
 
 (6) Take off the delivery tube from your gas bottle and sub- 
 stitute a straight tube which runs to the bottom of a dry test 
 
FLAME 47 
 
 tube clamped in a horizontal position. In this test tube is 
 1 c.c. of copper oxide powder. If necessary, add more acid 
 through the funnel tube. Wait at least three minutes for the 
 air to be expelled, then heat the copper oxide. Note the change 
 in the copper oxide. Look in the cooler part of the tube for 
 the other product. Explain. What other element most re- 
 sembles hydrogen in its action on oxides ? 
 
 (c) Filter a few drops of the liquid which remains in the gas 
 bottle into a watch glass. Place it on a beaker half full of water, 
 support the beaker on wire gauze, and boil the water gently. 
 
 Describe in your notes the crystals which separate. They 
 are called zinc sulphate, and they contain zinc, sulphur, and 
 oxygen. Sulphuric acid contains hydrogen, sulphur, and oxy- 
 gen, so that we may describe the change which takes place in 
 the gas-generating bottle by the statement that the zinc takes 
 the place of the hydrogen. 
 
 EXERCISE 37 
 FLAME 
 
 Apparatus. Platinum wire. Wire gauze. Sheet copper 20 cm. 
 x 15 cm. (8 x 6 in.). Safety lamp. 
 
 Materials. Wooden splints. Pins. Glass tubing. Glass rod. 
 Charcoal. Candle. Touch paper. 1 Fine emery paper. Solution 
 of one part potassium dichromate in 20 parts water, to which has 
 been added one part sulphuric acid. Crayon. 
 
 Method. See textbook, pages 122, 123, and 124. 
 
 (a) Take the chimney off the Bunsen burner. Light the 
 gas at the tip in the base. Extinguish, replace the chimney, 
 close the air holes, and -light the gas. Do the size and shape 
 of the orifice from which the gas escapes affect the flame ? 
 Formerly, when the naked gas flame was much used for light- 
 ing, the determination of the area and shape of the orifice 
 which gave the best results was an important matter. 
 
 1 Dip strips of filter paper 1 cm. wide in a cold saturated solution of 
 potassium nitrate. Hang up to dry over a piece of glass tubing. 
 
48 LABORATORY STUDIES IN CHEMISTRY 
 
 Turn the luminous flame down to a height of 2 cm. (0.8 in.) 
 and hold a piece of crayon in it for a few seconds. Result? 
 Open the air holes and hold a fresh piece of crayon in the blue 
 flame for the same length of time. Result ? 
 
 Turn the blue flame to full height. Stand with your back 
 to the window and look through the flame at a dark back- 
 ground, e.g. the cover of a black book. Make a sectional draw- 
 ing of the flame as it appears to you, indicating the different 
 regions. Do the same with a candle flame. 
 
 The hottest part of the blue flame of the burner is level with 
 the tip of the inner blue cone. Verify this by moving a 
 platinum wire around in different regions, and noting where 
 it glows most brightly. Note also that it is possible to obtain 
 light from the blue flame by heating a solid body in it. This 
 fact has revolutionized the methods of lighting by gas. 
 
 Hold a piece of glass rod about 3 mm. (0.1 in.) in diameter 
 horizontally in the hottest portion of the blue flame until it 
 sags perceptibly. Note the time required in seconds to produce 
 this effect. Let the rod cool, and repeat with the luminous 
 flame. Use a different portion of the rod, and hold it at about 
 the same level in the flame as with the blue. Which flame 
 appears to be more satisfactory as a source of heat ? 
 
 Rub together two pieces of charcoal 1 cm. (0.4 in.) from the 
 open air holes at the base of the burner giving the blue flame. 
 Result ? Does this confirm your experiment with the crayon ? 
 Judging from this, what is the direction of motion through the 
 air holes ? Does gas escape or air enter ? Investigate this 
 further by holding a piece of smouldering touch paper 1 cm. 
 from the air holes. A splint which has just been blown out 
 can be used almost as well. 
 
 (6) Polish a flat piece of sheet copper 20 x 15 cm. (8x6 in.) 
 with fine emery paper. Hold it vertically in the center of the 
 flame with one edge resting on the burner. The time required 
 is only a few seconds. Judge by the eye when to remove it. 
 
 Thrust another portion of the copper horizontally through 
 the hottest portion of the flame for a few seconds. Examine 
 
FLAME 49 
 
 the two sections of the flame obtained. What is the chemical 
 nature of the discoloration on the copper ? What difference 
 does the experiment indicate regarding the chemical effects 
 which might be expected in different parts of the flame? 
 Wet the discolored parts of the copper with a glass rod which 
 has been dipped into a solution of potassium dichromate con- 
 taining sulphuric acid. Wash the copper and dry it. Card- 
 board or stiff paper can be used instead of copper, but some 
 skill is required to prevent ignition. 
 
 Hold in the center of the blue flame, 1 cm. above the bottom, 
 a glass tube open at both ends inclined at an angle of 45 
 upward. Bring the flame of a splint to the upper 
 end. Result ? Blow out a candle and instantly 
 apply a flame to the little column of smoke. Result ? 
 
 Thrust a wooden splint horizontally through the 
 blue flame of the burner 1 cm. above the base. With- 
 draw before it takes fire, and examine. Result? 
 Support a match by a pin as indicated in Fig. 18 
 and light the blue flame. 
 
 (c) Hold a piece of wire gauze horizontal and bring FIG 
 it down vertically upon the blue flame. The gauze 
 should be large enough to prevent the flame slipping around 
 the edge. Result? Extinguish the flame, turn on the gas, 
 and light it above the gauze. Result ? 
 
 If a miner's safety lamp is available, examine it and record 
 in your notes the peculiarity of its construction. Make a 
 sectional drawing of it. 
 
50 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 38 
 HYDROGEN SULPHIDE 
 
 Apparatus. Large test tube with rubber stopper and delivery tube 
 bent twice at right angles. Large test tube. Three small test tubes. 
 
 Materials. Iron sulphide in small fragments. Red and blue 
 litmus paper. Solutions of mercuric chloride, copper sulphate and 
 arsenious oxide. Sheet copper. 
 
 Method. Many metallic sulphides yield hydrogen sulphide with 
 hydrochloric or dilute sulphuric acid. (See textbook, pages 167, 168, 
 169): 
 
 FeS + 2 HC1 -> FeCl 2 +H 2 S. 
 
 CAUTION: Hydrogen sulphide is poisonous. Avoid inhaling it. 
 
 Place the large test tube almost horizontal and carefully 
 slide in enough iron sulphide to fill it 1 cm. (0.4 in.) deep. 
 Add water to the depth of 3 cm. (1.2 in.) and then hydrochloric 
 acid slowly until gas is briskly but not violently evolved. 
 Clamp the tube upright and insert the stopper bearing a deliv- 
 ery tube. Collect a dry test tube of the gas by downward dry 
 displacement. Light the gas in the test tube, after removing 
 the delivery tube. 
 
 What are the two products of combustion ? What evidence 
 have you of the formation of each ? What conclusion can you 
 draw with respect to the composition of the gas ? 
 
 Hold a piece of clean sheet copper close to the exit tube of 
 your apparatus. A silver coin. Result ? 
 
 Nearly fill a large test tube with water and let the gas escape 
 through it for several minutes, running the delivery tube to 
 the bottom. Stop the production of gas by filling the generat- 
 ing tube with water and pouring away the liquid. Use sepa- 
 rate small portions of the solution of hydrogen sulphide for 
 the following experiments. In each case, place the hydrogen 
 sulphide solution in a test tube and add a few drops of a solu- 
 tion of the substances mentioned. 
 
 (a) Copper sulphate. 
 
 (6) Mercuric chloride. 
 
AMMONIA 51 
 
 (c) Arsenious oxide. 
 
 In (c) after noting the result, add a few drops of hydrochlo- 
 ric acid. Result ? 
 
 Taste a little of the original hydrogen sulphide solution. 
 Investigate its action on both kinds of litmus paper. 
 
 EXERCISE 39 
 AMMONIA 
 
 Apparatus. Large test tube, with stopper and delivery tube bent 
 once at a right angle. Perforated square of cardboard. Two glass 
 plates. Evaporating dish. Three small test tubes. Large test tube. 
 Two bottles. Glass rod. 
 
 Materials. Glue. Ammonium chloride. Ammonium sulphate. 
 Dry slaked lime. Red litmus paper. 
 
 Method. See textbook, pages 170, 172, 173. 
 
 A mixture of ammonium chloride and slaked lime yields am- 
 monia : 
 
 2NH 4 C1 + Ca(OH) 2 ->CaCl 2 + 2 H 2 O + 2NH 3 . 
 
 (a) Formation from organic matter. Mix 1 c.c. of glue, 
 powdered if necessary, with twice its volume of dry slaked 
 lime. Heat the mixture gently in a dry, small test tube. Do 
 not scorch the glue. Note the odor of the gas given off and its 
 effect upon red litmus paper. After testing with litmus hold a 
 glass rod wet with hydrochloric acid in the gas. Almost any 
 organic matter containing nitrogen will yield ammonia if 
 treated in this way. This can serve, therefore, as a test for 
 nitrogen in such substances. 
 
 (b) Formation from ammonium salts. Take 1 c.c. of ammo- 
 nium chloride in one hand and an equal volume of slaked lime 
 in the other. Notice the odor of each. Rub together. Note 
 odor and apply the same tests as in (a). 
 
 Repeat with ammonium sulphate and slaked lime. 
 
 (c) Preparation. Place enough ammonium chloride on a 
 piece of paper to fill your generating test tube 5 cm. (2 in.) 
 
52 
 
 LABORATORY STUDIES IN CHEMISTRY 
 
 deep. Add an equal volume of slaked lime. Mix well. Trans- 
 fer to the test tube. Support the latter in a horizontal position 
 as indicated in Fig. 19. The delivery tube passes upward 
 through a perforated card or piece of pasteboard held by a ring 
 on the upper part of the stand. The tube should reach to the 
 bottom of the inverted bottle. Warm gently. Use a small flame. 
 Avoid heating the wet portion of the tube, or breakage will re- 
 sult. Collect a dry bottle and a dry test 
 tube full of the gas. Test when the 
 bottle is full by holding a rod wet with 
 hydrochloric acid just below the perfora- 
 tion in the cardboard. Slight fumes can 
 be disregarded. A dense, white smoke 
 indicates that the bottle is full and 
 ammonia is escaping. Place the bottle 
 mouth downward upon a glass plate 
 until you are ready to use it. Keep the 
 generator for (d). 
 
 Place your test tube of ammonia with 
 the mouth under water in a dish. 
 Shake gently. Result ? Warm a clean, 
 dry bottle by passing it rapidly through 
 the burner flame. Holding it in the 
 flame will crack it at once. Place in 
 the bottle five drops of concentrated 
 
 hydrochloric acid and run the acid around the walls as much 
 as possible, holding the bottle upright and keeping it covered 
 with a glass plate. Now bring it mouth to mouth with the 
 bottle of ammonia and remove both plates, keeping the 
 bottles in contact. Invert the bottles several times, keeping 
 them mouth to mouth. What is the deposit ? Write the 
 equation. 
 
 (cf) Turn the delivery tube downward and bring it just in 
 contact with the surface of 5 c.c. of water in a small test tube. 
 Pass in the gas for five minutes. What is the action of the 
 liquid on red litmus paper ? What hydroxide must it contain ? 
 
 FIG. 19. 
 
NEUTRALIZATION OF AMMONIUM HYDROXIDE 53 
 
 Show by the tests of (a) that this hydroxide is decomposed 
 and the ammonia driven out, by heating the liquid. 
 
 Place 5 c.c. strong ammonia water from your stock bottle in 
 a small test tube and clamp in an inclined position with the 
 clamp about at the middle of the tube. Slip a large, dry in- 
 verted test tube over it. Boil gently one minute. Keeping 
 the large tube inverted, plunge its mouth under water in a 
 dish. From the result deduce conclusions regarding (1) the 
 solubility of ammonia in water, (2) the effect of heat upon its 
 solubility. 
 
 EXERCISE 40 
 
 NEUTRALIZATION OF AMMONIUM HYDROXIDE 
 BY ACIDS 
 
 (Ammonium /Salts) 
 
 Apparatus. 100 c.c. graduated cylinder. Hard glass tubing 1 cm. 
 or more in diameter. Pipestem triangle. Porcelain crucible lid. 
 Beaker. Evaporating dish. Glass rod (thin). Triangular file. Bottle. 
 
 Materials. Red and blue litmus paper. Ammonium chloride. 
 Ammonium sulphate. Ammonium nitrate. Concentrated hydro- 
 chloric acid. Ammonia-water. 
 
 Method. See textbook, pages 236, 237, 238, 287, 302. 
 
 (a) Place in the graduated cylinder 10 c.c. concentrated 
 hydrochloric acid. Read from the bottom of the meniscus 
 (Fig. 4). Dilute to 100 c.c. with water and stir well. 
 Transfer 20 c.c. of this dilute acid to a. dry beaker and put 
 the rest in a bottle in case of need. 
 
 Wash the cylinder and rinse it with a few drops of strong 
 ammonia. Dilute 10 c.c. of ammonia to 100 c.c. 
 
 Add this dilute ammonia gradually to the 10 c.c. of dilute 
 acid. Stir gently with a thin glass rod. Remember that the 
 beaker is thin and can be easily perforated. Continually test 
 whether you have added enough ammonia, by shaking most 
 of the liquid off the rod and placing a very small drop on red 
 5 
 
54 LABORATORY STUDIES IN CHEMISTRY 
 
 litmus paper. Use the same piece of paper for many tests. 
 When the paper is turned blue (what does this indicate?), 
 evaporate the liquid almost to dryness in a dish, using a very 
 small flame toward the end. Let cool. What is the residue ? 
 Write the equation. How does the equation differ from, the 
 one which you wrote in (c) of the preceding exercise ? 
 
 (&) Select a piece of hard glass tubing (Jena glass is best) 
 1 cm. or more in diameter, and cut a piece 20 cm. (8 in.) long. 
 Cut it by making a deep notch by sawing with a triangular file, 
 and bending away from the notch over the edge of the table. 
 Place 1 c.c. of ammonium chloride in the middle of the tube. 
 Introduce the ammonium chloride by means of a strip of paper 
 1 cm. (0.4 in.) wide which is folded along the center to make 
 a V-shaped trough. Put in each end of the tube a piece of 
 red and a piece of blue litmus paper. The litmus paper 
 should be damp. Clamp the tube nearly but not quite in a 
 horizontal position, putting the clamp 1 cm. from the end. 
 Heat the ammonium chloride gently. Watch the litmus paper 
 closely for changes, and for reversal of any changes which may 
 occur. Does the litmus paper show that the salt is decom- 
 posed by heat into ammonia and hydrochloric acid ? If so, does 
 the sublimate in the tube prove that the two gases must, for the 
 most part, reunite when they reach the cooler part of the tube ? 
 
 Let the glass tube cool, wash it, and return it. 
 
 (c) Support a porcelain crucible lid on a pipestem triangle. 
 Place on it a fragment of ammonium sulphate the size of the 
 head of a pin, and heat. Result ? Repeat with ammonium 
 nitrate. 
 
METHANE 55 
 
 EXERCISE 41 
 METHANE 
 
 Apparatus. Small test tube with delivery tube for collecting over 
 water. Bottle. Mortar and pestle. Agate pan. Glass plate. 
 
 Materials. Soda lime. Anhydrous sodium acetate (can be either 
 purchased or made by heating the crystallized salt in an iron dish 
 with constant stirring). Lime water. 
 
 Method. Methane is obtained when a mixture containing sodium 
 acetate and sodium hydroxide is heated : 
 
 NaC 2 H 3 O 2 + NaOH -+ Na 2 CO 3 + CH 4 
 
 Fill the test tube two thirds full with a mixture of equal vol- 
 umes of powdered soda lime and powdered anhydrous sodium 
 acetate. Clamp in a horizontal position. Tap the tube with 
 your pencil to make the powder settle and leave a channel 
 along the top for the escape of gas. Heat gently. Avoid 
 softening the glass by too high a temperature. Collect over 
 water. 
 
 Eecord the physical properties of the gas. Burn a bottle of 
 it and at once apply the limewater test. What product of 
 combustion do you detect? What other substance must be 
 formed by the combustion of methane ? 
 
56 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 42 l 
 CARBOHYDRATES 
 
 Apparatus. Wire gauze. Small test tubes. Beaker. Graduated 
 cylinder. Thin glass rod. 
 
 Materials. Glucose. Ordinary sugar. Molasses. Starch. Feh- 
 ling's solution (see below). Sodium carbonate. Red litmus paper. 
 
 Method. Glucose produces, with Fehling's solution, a red pre- 
 cipitate of cuprous oxide, Cu 2 O. 
 
 (1) 69.28 grams of powered copper sulphate (CuS0 4 5 H 2 0) 
 is dissolved in warm water and 10 drops of sulphuric acid 
 added. The solution is diluted to 1 liter in a graduated flask. 
 
 (2) 350 grams of Rochelle salt (potassium sodium tartrate, 
 KNaC 4 H 4 6 ) and 100 grams of sodium hydroxide are dissolved 
 together in water and the solution diluted to about 1 liter. 
 This liquid must be kept in a bottle with a rubber stopper. 
 
 The mixture of equal volumes of (1) and (2) is called 
 Fehling's solution. 1 c.c. of it interacts with 0.005 gram of 
 grape sugar (glucose, C 6 H 12 6 ). The two solutions should be 
 mixed just before use. Make 50 c.c. Fehling's solution by 
 mixing 25 c.c. of each in a graduated cylinder, stirring 
 thoroughly. 
 
 (a) In a test tube, dissolve about 0.5 c.c. of glucose in 20 c.c. 
 water. Heat 10 c.c. Fehling's solution in a beaker to gentle boil- 
 ing. Add two or three drops of the glucose solution. Result ? 
 The precipitate is cuprous oxide, Cu. 2 0. Add another drop of 
 the glucose solution and boil again. Continue in this way 
 until the liquid over the precipitate has become colorless. The 
 precipitate will remain red. Be careful to add no more glucose 
 solution than is necessary. What weight of glucose have you 
 added ? 
 
 (b) Dissolve about 0.5 c.c. cane sugar in 20 c.c. of water in a 
 beaker. Add a drop or two of this solution to 5 c.c. Fehling's 
 solution and heat in a test tube. Is there any result ? 
 
 1 The discussion of carbohydrates in textbook, Chapter 15, page 191, 
 should be read before this exercise is carried out. 
 
ACETIC ACID, WOOD ALCOHOL, ACETYLENE 57 
 
 To the rest of the sugar solution, add 10 drops concentrated 
 hydrochloric acid and heat on wire gauze for ten minutes to 
 gentle boiling. As the water evaporates, add enough water to 
 keep the volume at about 20 c.c. Cool and add solid sodium 
 carbonate until a drop of the liquid makes a blue spot on red 
 litmus paper. Then test with Fehling's solution in the same 
 way as before. What does the result show about the action of 
 acids on cane sugar ? Would acetic acid have produced the 
 effect as rapidly as hydrochloric ? Why ? The effect is due 
 entirely to the H ions. 
 
 (c) Boil 0.5 c.c. of starch powder with 20 c.c. of water and 
 repeat (6) w'ith the starch solution. What is the action of 
 dilute acids on starch ? What practical application is made 
 of the fact ? Why, in actual manufacture, is it sufficient to 
 neutralize the hydrochloric acid with sodium carbonate, instead 
 of removing it from the sirup (see textbook, page 193). Why 
 does hydrochloric acid act on the starch more rapidly than most 
 other acids ? The effect is due entirely to the H ions. 
 
 (d) Test a solution of 0.5 c.c. molasses in 20 c.c. water for 
 glucose. 
 
 EXERCISE 43 
 ACETIC ACID, WOOD ALCOHOL, ACETYLENE 
 
 Apparatus. Small test tubes. Bottle. Evaporating dish. 
 
 Materials. Acetic acid. Sodium acetate. Iron filings. Zinc 
 dust. Magnesium ribbon. Alcohol. Concentrated sulphuric acid, 
 lied and blue litmus paper. Wood alcohol. Asbestos fiber. Copper 
 wire No. 20. Iron wire. Limewater. Calcium carbide. 
 
 Method. See textbook, pages 183, 201, 202, 353. 
 
 (a) Take 10 c.c. of acetic acid in a small test tube. Record 
 its physical properties. Note the odor. Does it resemble that 
 of any common substance ? Add a few drops to a test tube 
 full of water. Taste the dilute acid and test it with red and 
 blue litmus paper. Place in one small test tube 1 c.c. of zinc 
 dust, in another, the same volume of iron filings, and in a third, 
 
58 LABORATORY STUDIES IN CHEMISTRY 
 
 a spiral made of 4 cin. of magnesium ribbon. Cover the metals 
 with concentrated acetic acid. If necessary, heat very gently 
 not to boiling with a small flame. What gas would you 
 expect to obtain? Is the change rapid and violent or slow 
 and moderate ? 
 
 Acetic acid is an inactive acid. Compare its activity with 
 that of an active acid (sulphuric), thus : Dilute 1 c.c. of acetic 
 acid with 4 c.c. of water. In another tube, place 4 c.c. of water 
 and add 1 c.c. of sulphuric acid. Add 1 c.c. of zinc dust to 
 each and compare the behavior. The same kind of chemical 
 process occurs in both tubes. The main difference is in the 
 speed. 
 
 (6) Place 1 c.c. of sodium acetate in a test tube, add 2 c.c. 
 of water and 1 c.c. of concentrated sulphuric acid. Warm 
 gently. Odor ? Effect on blue litmus paper ? In this experi- 
 ment, sulphuric acid produces acetic acid by interacting with 
 sodium acetate. 
 
 (c) To 1 c.c. of sodium acetate in a test tube add 2 c.c. 
 alcohol and 1 c.c. concentrated sulphuric acid. Warm gently for 
 an instant not to boiling. (Care !) Odor ? The fragrant sub- 
 stance is called acetic ester. It has some important applications ; 
 for instance, in the manufacture of smokeless powder from 
 guncotton. Its formation, in the way you have just carried 
 out, serves as a test for acetic acid or an acetate. 
 
 (d) Wood alcohol and formaldehyde. Note the odor of 
 wood alcohol and compare it with that of grain alcohol. The 
 odor is due to acetone, an impurity which is always present in 
 commercial wood alcohol. 
 
 Dip a mass of asbestos 1 cm. (0.4 in.) in diameter into wood 
 alcohol, place it on the base of your stand and set fire to it. 
 Hold over the flame a dry, cold, clean bottle. One product of 
 the combustion condenses on the walls. What is it ? To iden- 
 tify the other product, pour at once into the bottle 5 c.c. of 
 limewater, cover with the band and shake. Result? 
 
 Formaldehyde results from the imperfect combustion of 
 wood alcohol. Make a spiral by wrapping 30 cm, of No. 20 
 
CHLORINE 59 
 
 copper wire around a lead pencil. Heat the spiral red hot, 
 holding it with iron wire and hold it close to the surface of 
 2 c.c. of wood alcohol in a small test tube. The sharp odor is 
 due to formaldehyde. 
 
 (e) Acetylene. 
 
 Fill a small test tube completely with water, cover tightly 
 with the thumb, and invert it in an evaporating dish full of 
 water. Slip under the mouth of the tube a 5 mm. (0.2 in.) bit 
 of calcium carbide. If necessary, use another bit to complete 
 the filling of the tube. 
 
 The solid product in the dish is slaked lime (calcium hydrox- 
 ide). Test it with litmus paper (both kinds). 
 
 Remove the test tube from the dish, using the thumb, and 
 burn the gas. At once pour into the tube 5 c.c. of limewater, 
 cover with the thumb, and shake. What product of combus- 
 tion do you detect ? 
 
 EXERCISE 44 
 CHLORINE 1 
 
 Apparatus. A 300 c.c. flask with doubly perforated rubber 
 stopper, carrying a dropping funnel and a delivery tube bent twice 
 at right angles (Fig. 20). Kipp hydrogen generator (one will serve 
 for the class) . Four bottles. Small test tube with cork. Wire gauze. 
 Glass rod. Four glass plates. Iron spoon. 
 
 Materials. Potassium permanganate (commercial). Charcoal. 
 Red and blue litmus paper. Colored calico or other cotton fabric. 
 Fresh slaked lime. Ink. Christmas-tree candles. Iron wire No. 20. 
 
 Method. See textbook, pages 212, 213, 220. 
 
 Carry out this experiment under the hood. Avoid inhaling the gas. 
 Be sure that the cork of the apparatus Jits tightly. If the throat becomes 
 
 1 This exercise is given because it is included in the syllabi of College 
 Entrance Requirements. It may be dangerous in unskilled hands, and 
 it is certain to cause great discomfort to the students. Many teachers 
 will prefer to show it on the lecture table. However, the production of 
 the gas is under perfect control and the method is greatly superior to the 
 use of manganese dioxide and hydrochloric acid. 
 
60 
 
 LABORATORY STUDIES IN CHEMISTRY 
 
 irritated, place some alcohol in a beaker or on a handkerchief and inhale 
 the vapor. 
 
 If hoods are not available, this work should be omitted or done at a time 
 when the windows of the laboratory can be open. A little ammonia 
 sprinkled on the Jloor will reduce annoyance from chlorine. 
 
 Place crystals of potassium permanganate 1 cm. deep in the 
 flask. The substance need not be pure. Fit the flask with 
 a rubber stopper carrying a dropping funnel and a delivery 
 
 tube. Support it firmly on 
 wire gauze, and put a small 
 flame 8 cm. below it. Allow 
 hydrochloric acid to fall drop 
 by drop into the flask. Collect 
 by downward displacement 
 one small test tube and four 
 bottles full of the gas. Judge 
 when the vessel is full by the 
 color, and immediately cover it 
 tightly with a glass plate and 
 substitute another ; otherwise 
 the excess of chlorine will be 
 forced out at the top and make 
 the air unfit to breathe. Test 
 FIG. 20. tubes full of chlorine can be 
 
 corked. The exit tube of the 
 
 chlorine apparatus must reach to the bottom of the vessel. This 
 tube should be cut about a foot from the desk and united again 
 by a short piece of rubber tube, that it may be moved without 
 disturbing the apparatus. The vessel in which you are collect- 
 ing chlorine should be kept covered, and the exit tube slipped 
 between the cover and the side of the bottle. The bottles of 
 chlorine must be kept covered during all experiments. When 
 you have finished and desire to get rid of the chlorine, place 
 the bottles under the hood, remove the covers without breathing, 
 and at once retire to a distance. After the chlorine has escaped 
 which will require ten minutes the bottles can be cleaned. 
 
CHLORINE 61 
 
 Record the physical properties of the element. Invert a 
 test tube full in water and shake gently. Is it soluble ? 
 
 Lower l a hydrogen flame into a bottle of chlorine. If you 
 use a gas-generating bottle in this experiment, remember that 
 it must be allowed to run five minutes and that the generator 
 and stopper must be wrapped in a towel before lighting the 
 hydrogen. Describe the appearance of the flame of hydrogen 
 burning in chlorine. Hold a glass rod wet with ammonia near 
 an open bottle of hydrochloric acid. Result? This is a test 
 for hydrochloric acid. Now hold a rod wet with ammonia in 
 the gas left in the jar in which the hydrogen was burned. Is 
 it hydrochloric acid ? Has it the color of chlorine ? Heat a 
 piece of charcoal in a spoon until it begins to burn, and place 
 it in chlorine. Result? Keep the bottle covered. 
 
 Take out the charcoal and lower a lighted candle supported 
 on a wire into the same bottle of chlorine. The candle is com- 
 posed chiefly of compounds of hydrogen and carbon. The 
 black substance thrown off from the flame is carbon (soot). 
 Use the two preceding results to explain this one. What else 
 must be produced? Let the covered jar stand till the soot set- 
 tles and try the test with the glass rod wet with ammonia. 
 
 In the third bottle, place a bit of red litmus paper, a piece 
 of blue litmus paper, a strip of colored calico, and a fragment 
 of printed matter smeared over with writing ink until it is 
 illegible. Describe and explain the results. What is the most 
 important use of chlorine ? 
 
 In the fourth bottle, place some fresh slaked lime (milk of 
 lime answers well), and immediately cover the bottle tightly 
 with the palm of the hand and shake it'. Result ? Does the 
 chlorine disappear ? 
 
 Carefully add nitric acid, a few drops at a time, to the con- 
 tents of the bottle. What happens? What very important 
 technical process does this illustrate ? See textbook, page 317. 
 
 1 Many teachers will prefer to omit this experiment or to show it on 
 the lecture table. 
 
62 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 45 
 THE ACTION OF SULPHURIC ACID ON CHLORIDES 
 
 Apparatus. Four small test tubes. Glass rod. 
 Materials. Sodium chloride. Potassium chloride. Ammonium 
 chloride. Barium chloride. Red and blue litmus paper. 
 Method. See textbook, page 222. 
 
 Place 1 c.c. of sodium chloride in a small test tube. Do the 
 same with the other chlorides, using a different tube for each. 
 Drop into each tube 1 c.c. of concentrated sulphuric acid. 
 
 To show the behavior of water vapor with the gas given off, 
 blow across the mouth of the tube. Ascertain its reaction with 
 ammonia by holding a glass rod wet with this substance in the 
 tube. Remember, however, that any add vapor or gas will 
 give a white cloud with ammonia. In writing the equation 
 remember, also, that it is the gas (NH 3 ) given off by the 
 ammonia, and not the dissolved substance, which combines 
 with the hydrochloric acid. 
 
 Hold in each tube 1 sq. cm. of red and of blue litmus paper. 
 Result ? 
 
THE ACTION OF SULPHURIC ACID ON SALT 63 
 
 EXERCISE 46 
 THE ACTION OF SULPHUEIC ACID ON SALT 
 
 Apparatus. 300 c.c. flask, with singly perforated rubber stopper 
 and delivery tube bent twice at right angles. Beaker. Two small, 
 dry test tubes. Three dry bottles. Agate pan. Glass rod. Wire 
 gauze. 
 
 Materials. Table salt. Red and blue litmus paper. Christmas- 
 tree candles. Iron wire. Filter paper. 
 Method. See textbook, page 223. 
 
 Note the equation : 
 
 NaCl + H 2 SO 4 ^ NaHSO 4 + HC1. 
 
 Place about 25 c.c. of water in a beaker. Stand the beaker 
 in a pan of cold water and slowly pour in 50 c.c. concentrated 
 sulphuric acid, stirring constantly. Cool completely and pour 
 the liquid upon 30 grams of salt in the flask. 
 
 Place the flask on wire gauze and apply a gentle heat. 
 Collect, by downward displacement, two test tubes and three 
 bottles of hydrogen chloride. The delivery tube must reach 
 to the bottom of the bottle, and the bottle and delivery tube 
 must be dry. Why ? 
 
 Is hydrogen chloride soluble in water ? Try it by placing a 
 test tube full with its mouth downward in water. Does the 
 gas burn? Try with a test tube full. Does it support the 
 combustion of a candle ? How does it affect red and blue 
 litmus paper ? 
 
 Pour some ammonia 011 a wad of filter paper and throw it 
 into a bottle of hydrogen chloride. Result ? 
 
64 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 47 
 
 THE ACTION OF HYDROCHLORIC ACID ON SODIUM 
 HYDROGEN SULPHATE 
 
 Apparatus. Small test tube. Lens. 
 
 Material. Sodium hydrogen sulphate, NatISO 4 . 
 
 Method. See textbook, page 222. 
 
 Make 5 c.c. of a concentrated solution of sodium hydrogen 
 sulphate and add concentrated hydrochloric acid gradually. 
 
 Examine with a lens. The interaction of salt with sulphuric 
 acid, or of hydrochloric acid with sodium hydrogen sulphate, 
 is partial. It stops when all four substances, in certain fixed 
 quantities, are present in each c.c. of the liquid. In Exercise 45, 
 the escape of the hydrochloric acid removes it from the sphere 
 of the change and causes the reaction to proceed to completion 
 in one direction. In this exercise the insolubility of salt in 
 hydrochloric acid takes the salt out of the conflict and pushes 
 the reaction to completion in the other direction. 
 
 EXERCISE 48 
 
 THE ACTION OF HYDROCHLORIC ACID UPON 
 METALS 
 
 Apparatus. Beaker. Eight small test tubes. Medicine dropper. 
 Watch glass. 
 
 Materials. () Sodium. (b) Zinc (granulated and dust). Sheet 
 copper. Aluminium turnings. Test lead. Iron filings. Magnesium 
 ribbon. Mercury. 
 
 Method. See textbook, page 219, section 301. 
 
 (a) Drop a 2 mm. (no larger) piece of sodium into 5 c.c. of 
 concentrated hydrochloric acid in a small beaker. Does hydro- 
 gen escape ? Hold a burning match close to the globule. 
 Why is the flame of the burning gas yellow ? 
 
 (6) Dilute 20 c.c. of concentrated hydrochloric acid with 
 20 c.c. of water. Place in separate test tubes 1 c,e. of granu- 
 
ACTION OF HYDROCHLORIC ACID UPON METALS 65 
 
 lated zinc, zinc dust, aluminium turnings, iron filings, and test 
 lead. In a sixth tube place 1 sq. cm. of sheet copper, in a 
 seventh, 3 cm. of magnesium ribbon coiled into a spiral, and in 
 an eighth, 1 c.c. of mercury, using a medicine dropper. Add to 
 each tube 5 c.c. of the mixture of hydrochloric acid and water. 
 
 Notice and record any change in each tube. If no change 
 is evident, heat gently, but remember that gas escaping while 
 the flame is used may be steam or hydrogen chloride. If the 
 escape of gas continues while the flame is withdrawn, there is 
 evidence that the acid and the metal are interacting. Hydro- 
 gen can be identified by burning it, but remember that, when 
 much diluted with other gases, it does not burn. Does the 
 hydrogen come from the metal or the acid ? Arrange the 
 metals in a list, beginning with the most active. 
 
 When interaction occurs, there must be another product. 
 What must it be in each case ? 
 
 In order definitely to prove the formation of the second 
 product, evaporate one of the solutions to dryness in a watch 
 glass laid upon a beaker half full of water, which is gently 
 boiled. Wait until the action is over, and filter, if necessary, 
 before evaporating. 
 
 Did you notice any difference in the behavior of zinc dust 
 and granulated zinc ? If so, what is the cause ? 
 
66 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 49 
 
 THE ACTION OF HYDROCHLORIC ACID UPON 
 OXIDES 
 
 Apparatus. Two watch glasses 8.5 cm. in diameter. Five small 
 test tubes. Beaker. Funnel. 
 
 Materials. Magnesium oxide. Zinc oxide. Mercuric oxide. 
 Cupric oxide. Lead oxide. Filters. 
 
 Method. See textbook, page 221. 
 
 Place 1 c.c. of magnesium oxide in a small test tube. Do 
 the same with the other oxides, using a separate tube for each. 
 Add to each tube 2 c.c. of water and 2 c.c. of cone, hydro- 
 chloric acid. Warm gently, but not to boiling. Is gas 
 evolved ? Be careful to distinguish between mere boiling and 
 the escape of gas. The former ceases when the burner is 
 removed the latter continues. What becomes of the hy- 
 drogen of the acid and the oxygen of the oxide ? What, then, 
 must be the two products in each case ? 
 
 Complete the following equations, supplying coefficients 
 where needed: 
 
 MgO 
 ZnO 
 
 CuO + :rHCl->CuCl 2 +, 
 PbO + *HCl->PbCl 2 +. 
 
 Prove by evaporating some of the filtered liquids, as in the 
 preceding exercise, that these chemical changes occur. Use a 
 new filter for each substance and wash the funnel each time 
 before using it again. If time presses, the five evaporations 
 can be distributed to different students. 
 
 Contrast the behavior of hydrochloric acid with mercury and 
 with mercuric oxide (Exercise 48). 
 
 Contrast the behavior of hydrochloric acid with lead and 
 with lead oxide. 
 
FLAME TESTS 67 
 
 Contrast the behavior of hydrochloric acid with copper and 
 with copper oxide. 
 
 Contrast the behavior of hydrochloric acid with zinc and 
 with zinc oxide. Explain. 
 
 EXERCISE 50 
 FLAME TESTS 
 
 Apparatus. Wire cutter. Cobalt glass. Two small test tubes. 
 
 Materials. Nitrates of calcium, barium, strontium, sodium, and 
 potassium. The chlorides can be used instead. Solution of lithium 
 chloride. Iron wire No. 20. 
 
 Method. See textbook, pages 209, 241, 262, 312. 
 
 Obtain, on five small pieces of paper, 0.5 c.c. (not more) of 
 each of the nitrates mentioned. Take in a clean test tube 1 c.c. 
 (not more) of lithium chloride solution. Make a 2 mm. loop 
 on the end of a 15 cm. (6 in.) piece of iron wire. Dip the loop 
 and the adjacent part of the wire into a test tube (not the bottle) 
 containing 5 c.c. of concentrated hydrochloric acid, and hold it 
 in the blue flame of the burner until it gives no color to the 
 flame. Clean the wire in this way after each test, before using 
 it again. If you find it impossible to get the wire so clean that 
 it gives no color to the flame, discard it and get a fresh piece. 
 Discard the acid at the end of the work. 
 
 Take up a trace of calcium nitrate on the loop, hold it in the 
 lower, outer part of the flame, observe and record the color. 
 Do the same with each of the others. The wire may be mois- 
 tened when dipped into the salt. Or, if the wire is red hot, 
 enough of the salt will usually adhere to it to give the result. 
 
 Look at the potassium flame and also at the sodium flame 
 through cobalt glass. Which kind of light is quenched by the 
 glass and which transmitted ? Does this suggest a method of 
 detecting potassium in the presence of sodium? Mix the 
 nitrates of the two metals and look at the flame color of the 
 mixture without the glass. Which metal do you detect ? Now 
 use the glass. Eesult ? If a spectroscope is at hand, use it to 
 examine the spectrum of sodium. 
 
68 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 61 1 
 
 PREPARATION OF SODIUM HYDROGEN CARBON- 
 ATE AND SODIUM CARBONATE 
 
 (Solvay Process) 
 
 Apparatus. Gas-generating bottle with two-hole rubber stopper 
 bearing thistle tube and delivery tube, bent twice at right angles. 
 Test tube with one-hole rubber stopper and delivery tube. Iron dish 
 (porcelain will answer, with care). Graduated cylinder. Trip scales. 
 Large test tube with cork. Large test tube. 
 
 Materials. Table salt. Ammonium carbonate. Marble chips. 
 Sodium hydrogen carbonate. Filters. Manila paper. Limewater. 
 
 Method. See textbook, page 323. 
 
 (a) Place 25 c.c. strong ammonia and 15 c.c. water in the 
 large test tube and add 8 grams of ammonium carbonate (pow- 
 dered). Cork and shake until the latter is dissolved. Add an 
 excess of sodium chloride and shake persistently until the 
 liquid is saturated. 
 
 Decant the clear liquid into a test tube and pass in carbon di- 
 oxide in a slow stream for half an hour, or until an abundant 
 precipitate of sodium hydrogen carbonate separates. Mean- 
 while go on with (b) or (c). The carbon dioxide is made from 
 marble and hydrochloric acid (Exercise 21). Cover the marble 
 with water and add concentrated hydrochloric acid until you 
 obtain a steady evolution of gas. When the current of gas 
 slackens, add fresh acid. Filter the sodium hydrogen carbon- 
 ate and dry it between folds of manila paper. Note its appear- 
 ance and taste. 
 
 (6) Transformation of sodium hydrogen carbonate into so- 
 dium carbonate. 
 
 1 In order to finish in time, it is necessary to assign (a), (&), and (c) 
 to different groups of students. Or (a) may be carried out one week and 
 (&) and (c) the next, the sodium hydrogen carbonate being dried in the 
 meanwhile. The time required to saturate with carbon dioxide can be 
 reduced by drawing out the end of the delivery tube so as to produce 
 small bubbles. 
 
HYDROGEN FLUORIDE 69 
 
 Place 2 c.c. sodium hydrogen carbonate in a test tube and 
 support in a horizontal position. The delivery tube dips into 
 limewater. Heat gently, not hot enough to color the flame 
 yellow. What gas escapes ? What condenses in the cool part 
 of the tube ? Complete the equation: 
 
 + ... 4- - 
 
 Compare the taste of the product with that of sodium hydro- 
 gen carbonate. 
 
 (c) Weigh 10 grams of sodium hydrogen carbonate in a 
 weighed iron or porcelain dish. Heat at first gently, then in- 
 tensely. Let cool and reweigh. Compare the taste of the 
 product with that of sodium hydrogen carbonate. What is the 
 loss in weight ? Complete the equation in (6). Calculate 
 from the completed equation the amount which 10 grams should 
 lose. What is the error of your determination ? 
 
 EXERCISE 52 
 HYDROGEN FLUORIDE 
 
 Apparatus. Lead dish. Forceps. Glass rod. Agate pan. 
 Materials. Powdered fluorspar (calcium fluoride, CaF 2 ). Red 
 and blue litmus paper. Paraffin. Glass plate. Pins. 
 Methed. See textbook, page 263. 
 
 Place 2 c.c. of powdered fluorspar in the lead dish, moisten 
 but do not cover it with concentrated sulphuric acid, support the 
 dish 5 cm. (2 in.) above a small flame ; and .allow it to get warm. 
 Wet a glass rod with ammonia and hold it over the dish. Do 
 not let any ammonia fall into the dish. Remembering the 
 behavior of ammonia with hydrogen chloride (see textbook, 
 page 236), explain its behavior with the hydrogen fluoride, HF. 
 Write the equation for the combination of ammonia and 
 hydrogen fluoride and name the product. Hold over the dish a 
 piece of red and a piece of blue litmus paper. Both should be 
 damp. 
 
70 LABORATORY STUDIES IN CHEMISTRY 
 
 Complete the equation : 
 
 What is the advantage of using an acid like sulphuric, 
 which does not vaporize easily, in this experiment ? Why 
 would it be impossible to use hydrochloric or nitric acid, 
 although both are more active than sulphuric ? Compare 
 textbook, page 297. 
 
 Support a glass plate 10 cm. (4 in.) above a small flame. Rub 
 the upper side of the warm plate with a piece of paraffin until 
 you have covered it evenly. Let cool. Write the name of the 
 element which is combined with hydrogen in hydrogen fluoride 
 upon the plate with a pin, being careful to expose the glass. 
 Write also the year of the isolation of fluorine and the name 
 of the great French chemist who first isolated it. (See text- 
 book, page 264.) Cover the dish with the plate, paraffin side 
 down, in such a way that your writing is completely exposed to 
 the gas in the dish. Let stand for half an hour or more. The 
 warmer the place, the better. Do not heat with the flame. 
 Drop the plate into a pan of boiling water to remove the 
 paraffin. Take it out with forceps, wipe, and examine. 
 
BROMINE 71 
 
 EXERCISE 53 
 BROMINE 
 
 Apparatus. Large test tube. Four small test tubes. Glass rod. 
 
 Materials. Potassium bromide (powder). Manganese dioxide 
 (powder). Potassium iodide solution. Chloroform. Ether. Car- 
 bon disulphide. Bromine. Red and blue litmus paper. Potassium 
 iodide starch paper. 1 
 
 Method. See textbook, pages 260, 261, 262. Note the equation : 
 
 2 NaBr + Mn0 2 + 3H 2 SO 4 ->- MnSO 4 + 2 NaHSO 4 + Br 2 . 
 
 (a) Place 1 c.c. water in a small test tube. Add 2 c.c. con- 
 centrated sulphuric acid. Cool. Mix 1 c.c. potassium bromide 
 powder with 2 c.c. manganese dioxide powder on paper and 
 place in another test tube. Add enough of the diluted sul- 
 phuric acid to moisten the mass. Warm gently. Bromine 
 vapor escapes. Note color and odor. (Care!) Hold in the 
 vapor a drop of potassium iodide solution (glass rod). If the 
 color in the drop is due to liberated iodine, what else must be 
 formed at the same time ? 
 
 Hold a piece of potassium iodide-starch paper in the vapor. 
 Potassium iodide does not color starch, as the whiteness of 
 the unused paper proves. Iodine, on the other hand, colors 
 starch deep blue (delicate test both for iodine and starch). 
 Explain, then, the behavior of the paper in bromine vapor. 
 
 Remove the flame and stop the production of bromine by 
 filling the tube with water. Other soluble bromides would 
 behave like potassium bromide in this. experiment, and other 
 soluble iodides like potassium iodide. The potassium salts 
 are used merely because they are most easily obtained. 
 
 CAUTION: Ether and carbon disulphide must not be used in the 
 vicinity of flame. Bottles containing them must be kept stoppered. 
 
 1 To make this, boil 1 c.c. starch powder with 100 c.c. water, add a 
 1 mm. crystal of potassium iodide, dip strips of filter paper 1 cm. wide 
 in the liquid, and hang them over a piece of glass tubing to dry. 
 
72 LABORATORY STUDIES IN CHEMISTRY 
 
 (6) Add one drop of bromine to 15 c.c. of water in a small 
 test tube. Shake the liquid in the test tube. The solution 
 you have made is called bromine water. Place 5 c.c. of it in 
 each of the three small test tubes. 
 
 CAUTION: Do not withdraw the stopper of the bromine bottle alto- 
 gether. Loosen it and let the liquid drip out between stopper and bottle. 
 Use the opportunity to notice the high density of bromine. Avoid inhaling 
 bromine vapor. 
 
 To one tube, add 2 c.c. of ether, cover with the thumb and 
 shake. The color serves as a measure of the concentration of 
 the bromine in the two layers. What happens to the bromine ? 
 Note that the bromine does not pass completely from the water 
 to the ether layer. Whether there is much or little bromine 
 present, it is divided between the water and the ether so that 
 the value of the fraction 
 
 bromine in 1 c.c. water layer 
 bromine in 1 c.c. ether layer 
 
 is always the same and very much less than unity. 
 
 If you had to extract the bromine as completely as possible 
 from a liter of bromine water, and could use only 500 c.c. of 
 ether, how would you go about it ? Would it be best to use 
 the ether all at once ? Or could you get a better result by 
 shaking up with a small portion of ether first, separating the 
 ether solution of bromine, shaking up the water again with 
 another small portion of ether, and so on ? Why ? (Compare 
 textbook, page 31, section 40.) 
 
 Try, in the second tube, 2 c.c. of chloroform, and in the third, 
 2 c.c. of carbon disulphide. Cover and shake as before. In 
 these cases, also, the water competes with the other liquid for 
 the bromine. 
 
 (c) Hydrogen bromide. Place 1 c.c. of potassium bromide 
 crystals in a test tube and cover with a mixture of 3 volumes 
 of sulphuric acid and 1 volume of water. Use a gentle heat. 
 Try the action of the gas upon red and blue litmus paper. 
 
IODINE 73 
 
 Hold a drop of ammonia in the gas. Make a comparison be- 
 tween hydrogen bromide and hydrogen chloride. 
 
 Pure hydrogen bromide is colorless. Had the gas any color 
 in this experiment? Eecalling the color of bromine vapor, 
 what did the color of your gas in this experiment indicate ? 
 Draw a conclusion regarding the stability of hydrogen bromide 
 as compared with hydrogen chloride. Hydrogen iodide (HI) 
 cannot be prepared at all by the action of sulphuric acid on 
 iodides, because it is, for the most part, decomposed with 
 liberation of iodine. (See textbook, page 259.) How about 
 its stability? Inquire of the instructor about the stability 
 of the hydrogen compounds of this series and read up the 
 matter in the textbook, page 267. 
 
 EXERCISE 64 
 IODINE 
 
 Apparatus. Watch glass (large enough to cover evaporating 
 dish). Graduated 100 c.c. cylinder. Evaporating dish. Two large 
 test tubes, one of which must be dry. Four small test tubes. 
 
 Materials. Potassium iodide. Iodine. Manganese dioxide 
 (powder). Starch solution. Alcohol. Ether. Carbon disulphide. 
 Chloroform. Filter paper. 
 
 Method. See textbook, pages 258, 259, 260. Note the equation : 
 2 KI + MnO 2 + 3 H 2 SO 4 ->MnSO 4 + 2 KHSO 4 + I 2 . 
 
 CA UTION: Do not allow iodine to come into contact with the skin. 
 
 (a) Place 1 c.c. of water in a small test tube and add 2 c.c. 
 concentrated sulphuric acid. Cool. Mix 1 c.c. powdered 
 potassium iodide with 2 c.c. manganese dioxide powder on 
 paper. Transfer to a dry dish. Moisten the mixture with 
 three to four drops of the diluted sulphuric acid. Cover the 
 dish with a watch glass which is two thirds rilled with cold 
 water to keep it cool. Support the dish 10 cm. (4 in.) above a 
 2 cm. (0.8 in.) flame. When a sufficient sublimate collects on 
 
74 LABORATORY STUDIES IN CHEMISTRY 
 
 the watch, glass, extinguish the flame. Dip a strip of filter 
 paper into starch solution and hold it in the vapor from the 
 dish. Result ? Examine the sublimate on the watch glass. 
 
 Iodine stains upon the hands can be removed by rubbing 
 with a wet crystal of sodium thiosulphate (commonly called 
 hyposulphite or hypo). 
 
 (6) Gently warm a large test tube and throw in a crystal of 
 iodine. Notice color and odor of iodine vapor. Invert the 
 tube and notice the high specific gravity of iodine vapor. If 
 the formula of iodine is I 2 , what would the specific gravity of 
 the vapor be, referred to oxygen ? Referred to air ? 
 
 Use the same test tube to study the solubility of iodine in 
 alcohol. Take one crystal of iodine and 3 c.c. alcohol. Shake. 
 This alcoholic solution of iodine is called tincture of iodine in 
 pharmacy. 
 
 CAUTION: Ether and carbon disulphide must not be used near a 
 fiame. 
 
 Fill a large test tube one half with water, add three crystals of 
 iodine, warm, not quite to boiling-point and shake. Judge 
 of the solubility of iodine in water by the color of the liquid. 
 Place 10 c.c. of the clear solution in each of four small test 
 tubes. Use three of these to ascertain the effect of shaking 
 (1) with 2 c.c. ether, (2) with 2 c.c. chloroform, (3) with 2 c.c. 
 carbon disulphide. Discuss the results from the same point of 
 view as the similar experiments with bromine (Exercise 53). 
 
 To the fourth tube, add 10 c.c. starch solution. Mix thor- 
 oughly. Reserving the remainder of the blue liquid, pour 
 1 c.c. of it into a clean graduated cylinder. The cylinder now 
 contains 0.0001 gram of iodine. Add water to the 100 c.c. mark 
 and mix thoroughly by covering the cylinder with the hand 
 and upsetting it several times. 
 
 Now pour off half the liquid, fill again to 100 c.c., and mix. 
 Place the cylinder on a piece of white paper and look down 
 through it. How much iodine does the cylinder now contain ? 
 Proceed in this way until it becomes impossible to perceive 
 the color. 
 
SILVER COMPOUNDS OF THE HALOGENS 75 
 
 What is the smallest quantity of iodine which you can de- 
 tect by means of the test with starch. Is the test delicate ? 
 
 Heat the remainder of the original mixture of iodine and 
 starch solution nearly to the boiling point (80). Eesult? 
 Cool at once in a stream of water. Eesult ? 
 
 EXERCISE 65 
 SILVER COMPOUNDS OF THE HALOGENS 
 
 (Tlie Replacement of One Halogen by Another) 
 Apparatus. Porcelain dish. Six small test tubes. 
 Materials. Chlorine water. Bromine water. Potassium bromide. 
 Potassium iodide. Carbon disulphide. Potassium chloride. Silver 
 nitrate solution. Salt. Mossy zinc. Distilled water. 
 Method. See textbook, pages 260 and 261. 
 
 CA UTION: Do not allow silver nitrate or its solution to come into 
 contact with the skin. 
 
 (a) * Dissolve 0.5 c.c. sodium chloride in 5 c.c. distilled water 
 and add 3 c.c. silver nitrate solution. Shake vigorously. 
 Transfer the precipitate, by rinsing with water, to a dish, pour 
 off the water, add a 0.5 cm. bit of mossy zinc and one drop of con- 
 centrated sulphuric acid. Cover with a paper to exclude the 
 light and examine from time to time. The visible product is 
 silver. What else must be formed ? Notice that the change 
 spreads through the mass and that the silver chloride is all con- 
 verted into silver, although most of it never touches the zinc at 
 all. This might be called chemical action at a distance. It can 
 be readily explained, using the ideas of the ionization hypothesis, 
 but the full explanation lies beyond the scope of this book. 
 Remove the unused zinc, wash the silver well with water, and 
 ask the instructor what to do with it. 
 
 (b) Dissolve a 1 mm. crystal of potassium chloride in 5 c.c. 
 
 1 (a) and (6) should be started at the beginning of a laboratory period 
 and allowed to stand until near the end. 
 
76 LABORATORY STUDIES IN CHEMISTRY 
 
 of distilled water in a small test tube. In two other tubes, 
 dissolve 1 inm. crystals of potassium bromide and potassium 
 iodide each in 5 c.c. distilled water. Add to each tube 1 c.c. 
 silver nitrate solution and shake. Names and formulas of the 
 precipitates ? Equations ? Use half of each precipitate to 
 study the solubility in ammonia. Result ? Stand the other 
 half in bright sunlight or the brightest light available as long 
 as possible. Result ? 
 
 CA UTION : Carbon disulphide must not be used near aflame. 
 
 (c) Dissolve a 1 mm. crystal of potassium bromide in 5 c.c. 
 water in a small test tube. Add 2 c.c. carbon disulphide and 
 shake. Does chemically combined bromine behave like free 
 bromine toward carbon disulphide ? To discuss the result ac- 
 curately, we should use the language of the hypothesis of ion- 
 ization. The water solution of potassium bromide contains 
 bromine ions (Br). These are colorless. Also they are held 
 tenaciously by the water and scarcely enter the carbon disul- 
 phide at all. 
 
 Now add 3 c.c. chlorine water and shake. Result? The 
 result can be summed up in the statement that the chlorine 
 combines with the potassium, setting free the bromine, which 
 dissolves in the carbon disulphide. Speaking in terms of the 
 ionization-idea, the chlorine (C1 2 ) takes the negative charges 
 from two bromine ions, producing two chlorine ions (Cl) and 
 bromine (Br 2 ), which dissolves in the carbon disulphide. 
 
 The result may be said to prove that the " affinity " of chlo- 
 rine for potassium is greater than that of bromine. It would 
 be more exact to say that it shows that the tendency of chlo- 
 rine to exist as an ion is greater than that of chlorine. 
 
 (d) Repeat (c), using a 1 mm. crystal of potassium iodide, 
 instead of the potassium bromide. Which has the " strongest 
 affinity " for potassium, chlorine or iodine ? More exactly, 
 which has the strongest tendency to exist as ion ? 
 
 (e) Repeat (c), using a 1 mm. crystal of potassium iodide 
 
NEUTRALIZATION (1) 77 
 
 with the water and carbon disulphide as before, but, instead of 
 the 3 c.c. chlorine water, add 0.5 c.c. bromine water and shake. 
 Which has the " strongest affinity " for potassium, bromine or 
 iodine ? Which has the strongest tendency to exist as ion ? 
 
 EXERCISE 56 
 NEUTRALIZATION (1) 
 
 Apparatus. Beaker. Porcelain dish. Lens. Glass rod. 
 Materials. Sodium hydroxide. Potassium hydroxide. Red and 
 blue litmus paper. 
 
 Method. See textbook, pages 245 and 246. 
 
 CA UTION : Do not allow potassium hydroxide or sodium hydroxide 
 to come into contact with the skin. 
 
 (a) Let concentrated hydrochloric acid fall, drop by drop 
 (Care /), upon a 2 cm. (0.8 in.) piece of sodium hydroxide in a 
 beaker. It is best to withdraw the stopper partially and allow 
 the acid to leak out between the stopper and the bottle. From 
 time to time put a small drop of the liquid upon red and a drop 
 upon blue litmus paper, using a thin glass rod. Use the same 
 paper for many tests. 
 
 When the stick is disintegrated and the change seems com- 
 plete (acid reaction to litmus), -scrape the solid product into a 
 dish and dry it with a small flame kept in motion. When 
 entirely dry and odorless, let cool and taste. Note shape of 
 the crystals with a lens or microscope. What is the solid? 
 What must have been the second product ? Write the equa- 
 tion. 
 
 (6) Let concentrated nitric acid fall, drop by drop, upon a 
 2 cm. piece of potassium hydroxide (Care !) until the change is 
 complete (litmus paper). Dissolve the result in the smallest 
 possible quantity of hot water and let cool. Shape and appear- 
 ance of the crystals ? Equation ? 
 
78 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 67 
 
 NEUTRALIZATION (2) 
 
 (Quantitative) 
 
 Apparatus. Burette. Graduated cylinder. Balance or trip scales. 
 Beaker. Porcelain dish. Thin glass rod. 
 
 Materials. Normal acid. 1 Sodium hydroxide. Potassium hy- 
 droxide. Litmus solution. Cochineal solution. 
 
 Optional. Washing soda. Commercial potassium carbonate. 
 Limewater. 
 
 Method. See textbook, page 256. 
 
 Read up the subject of neutralization and normal acids in the 
 textbook, page 256. One cubic centimeter of a normal acid 
 neutralizes the molecular weight in milligrams of sodium hy- 
 droxide or potassium hydroxide, but only one half the molecular 
 weight of sodium carbonate or potassium carbonate. 
 
 Clamp the burette in a vertical position. Note that it reads 
 downward. Thus, when halfway between 9 and 10, the reading 
 is 9.5 c.c., not 10.5. If the burette is wet, rinse it out with a few 
 drops of the normal acid and discard the latter. Dry beakers 
 must be used in handling the normal acid, to avoid diluting it. 
 
 (a) Dry a dish, weigh it, and weigh in it 4 grams of sodium 
 hydroxide. Add 50 c.c. water and dissolve the sodium hydroxide 
 by stirring, using a gentle heat if necessary. Transfer to a 
 graduated cylinder and rinse the dish into the cylinder three 
 times with small quantities of water. Dilute to 100 c.c. Mix 
 thoroughly. 
 
 1 Most quickly made by dissolving 63 grams oxalic acid (C 2 H 2 O 4 , 2 H 2 0) 
 to a liter. Trip scales are accurate enough for the weighing. It is well 
 to have at least 75 c.c. for each student ; more, if the work is extended to 
 cover sodium carbonate, pearlash, etc. The student can readily make it 
 himself in the graduated cylinder, but the exercise then becomes too long 
 for the usual laboratory period. Use cochineal as indicator in presence 
 of carbonic acid. Digest a 1 cm. layer of the crushed insects under half 
 a liter of alcohol with occasional shaking. Other indicators may be sub- 
 stituted. Mohr burettes are best suited to elementary work. 
 
NEUTRALIZATION (2) 79 
 
 Pour exactly 20 c.c. of the solution of sodium hydroxide into 
 a clean beaker, and add enough litmus solution to give a dis- 
 tinct but not a strong color (about five drops). Fill the burette 
 to zero with the normal acid, making sure that the portion 
 below the pinchcock is also filled. Stand the beaker on a piece 
 of white paper (filter paper) and run in the normal acid 
 10 c.c. can be added rapidly ; then add one drop at a time, stir- 
 ring constantly, until the color change occurs. Calculate the 
 percentage of sodium hydroxide in the sample. Remember 
 that 20 c.c. contains ^ of the quantity weighed out. Thus, 
 suppose that 19 c.c. of the normal acid were required. Since 
 each cubic centimeter of the normal acid consumes 40 milli- 
 grams of sodium hydroxide, the quantity of the latter present 
 must have been, in grams, 0.040 x 19 = 0.76 gram NaOH. 
 The 20 c.c. of sodium hydroxide solution used contained 
 4 X ^ = 0.8 gram commercial NaOH. So the percentage of 
 true sodium hydroxide must be : 
 
 =95 per cent, the balance being impurities. 
 
 0.8 
 
 Repeat, using 25 c.c. of the sodium hydroxide, colored with 
 10 drops of cochineal solution instead of litmus. Does the 
 volume of sodium hydroxide solution taken affect the result ? 
 Does the nature of the indicator affect it ? Remember that 
 25 c.c. contains ^ of the quantity of sodium hydroxide you 
 weighed out. 
 
 If the sodium hydroxide had been perfectly pure, what 
 special concentration would have been obtained by using 4 
 grams of it in 100 c.c. ? To what extent did your solution 
 depart from this concentration? 
 
 (6) Weigh in a dish 5.6 grams potassium hydroxide and 
 repeat the whole experiment, making the same calculations 
 and answering the same questions. 
 
 In (c) and (d) use cochineal and omit the experiment with 
 litmus. 
 
 (c) Make the same experiment with 14.3 grams of washing 
 
80 LABORATORY STUDIES IN CHEMISTRY 
 
 soda crystals. Calculate the percentage of sodium carbonate, 
 Na 2 C0 3 . How close is your result to that calculated from the 
 formula Na^CQilOBW)? 
 
 (d) Make the same experiment with 6.9 grams commercial 
 potassium carbonate (pearlash). Calculate the percentage of 
 potassium carbonate, K 2 C0 3 . 
 
 (e) Measure 100 c.c. of limewater into a beaker, color with 
 litmus or cochineal, and add normal acid from the burette until 
 the change in color takes place. Be careful, as only a small 
 volume of acid will be needed. Since the molecular weight of 
 Ca(OH) 2 is 74, 1 c.c. of normal acid equals -^ or 37 milligrams 
 of slaked lime. Calculate the weight of calcium hydroxide in 
 100 c.c. of limewater. 
 
 According to the most exact figures obtainable, 100 c.c. lime- 
 water at room temperature (20 C.) contains 0.165 gram calcium 
 hydroxide. What was the error of your result ? The white 
 precipitate formed is calcium oxalate : 
 
 Ca(OH) 2 + H 2 C 2 4 ->CaC 2 4 + 2 H 2 O. 
 
 EXERCISE 68 
 THE ACTION OF BASES ON SALTS 
 
 Apparatus. Beaker. Small test tubes. Mortar and pestle. 
 
 Materials. Sodium hydroxide. Copper sulphate. Silver nitrate. 
 Mercuric chloride. Zinc sulphate. Lead nitrate. Aluminium sul- 
 phate. Ferrous sulphate. Mercuric oxide. 
 
 Method. The hydroxides of the heavy metals (see textbook, 
 page 368) are mostly insoluble in water. They precipitate when 
 sodium hydroxide solution is added to a solution containing a salt of 
 the corresponding metal. Some insoluble hydroxides dissolve in ex- 
 cess of sodium hydroxide solution. 
 
 (a) Dissolve 10 grams of sodium hydroxide in 80 c.c. water 
 in a beaker. Aid the solution by a small flame and gentle 
 stirring. Cool the liquid. Dissolve 0.5 c.c. copper sulphate 
 in 5 c.c. water in a small test tube. Cool, if you have used 
 
THE ACTION OP BASES ON SALTS 81 
 
 heat. Add 5 c.c. of the sodium hydroxide solution. Complete 
 the equation : 
 
 Heat the contents of the tube to gentle boiling. Kesult ? 
 
 Repeat, using a 1 mm. crystal of silver nitrate instead of the 
 copper sulphate. Boiling is necessary only in the case of cop- 
 per sulphate. Handle silver nitrate with paper, not with the 
 fingers. Complete the equation : 
 
 x AgNO 3 + y NaOH->Ag 2 O 
 
 Repeat, using 0.5 c.c. of mercuric chloride. Complete the 
 equation : 
 
 HgCl 2 -f x NaOH -> HgO + y NaCl + . .. . 
 
 Compare this mercuric oxide with that in the stock bottle. 
 Chemists are not yet agreed upon the cause of the striking 
 difference. 
 
 (b) Dissolve 0.5 c.c. zinc sulphate in 5 c.c. water. Add 
 sodium hydroxide solution, a few drops at a time, shaking well 
 after each addition. When a considerable precipitate is ob- 
 tained, stop to examine it and then continue the addition of 
 sodium hydroxide until you have added 10 c.c. Complete the 
 equation : 
 
 What happens when more sodium hydroxide is added to the 
 precipitate ? 
 
 Treat lead nitrate in the same way as zinc sulphate. Com- 
 plete the equation : 
 
 Pb(NO 3 ) 2 + zNaOH -> Pb(OH) 2 + .... 
 
 Treat aluminium sulphate in the same way as zinc sulphate. 
 Complete the equation : 
 
 A1 2 (S0 4 ) 3 + zNaOH -> 2 A1(OH) 3 + .... 
 
 What important difference exists between the substances in 
 (a) and those in 
 
82 LABORATORY STUDIES IN CHEMISTRY 
 
 (c) Select a clear crystal of ferrous sulphate about 0.5 cm. 
 in diameter and hold it in a stream of water until the surface 
 is dissolved away. Dry with paper and crush in a clean 
 mortar. Powder finely. 
 
 Boil 10 c.c. water in a small test tube to expel the dissolved 
 air and cool in a stream of water. Add the ferrous sulphate 
 and dissolve it by stirring. Do not heat. When completely 
 dissolved, add 10 c.c. sodium hydroxide solution. The precip- 
 itate is ferrous hydroxide. Complete the equation : 
 
 FeSO 4 + arNaOH -> Fe(OH) 2 + .... 
 
 Shake the tube vigorously for five minutes and note any 
 change in the precipitate. It passes into ferric hydroxide. 
 The complete equation is : 
 
 2 Fe(OH) 2 + O + H 2 O -> 2 Fe(OH) 3 . 
 
 EXERCISE 59 
 
 THE ACTION OF A METAL ON A SOLUTION OF A 
 SALT OF ANOTHER METAL 
 
 Apparatus. Scissors. Tinner's shears. Lens. Ten small test 
 tubes. 
 
 Materials. (a) Sheet copper. Sheet zinc. Copper wire No. 30. 
 (b) Silver nitrate. Mercuric chloride. Copper sulphate. Lead nitrate. 
 Tin chloride (stannous). Zinc sulphate. Sandpaper. Dennison 
 labels, small. 
 
 Method. See textbook, page 293. 
 
 (a) Cut a piece of sheet copper 5x5 cm. (2x2 in.). 
 Clean it with sandpaper and cut it into five strips each 5x1 
 cm. (2 x 0.4 in.). Prepare, in the same way, five strips of 
 sheet zinc. 0.5 cm. from the end of each of the ten metal 
 strips fasten one end of a copper wire 20 cm. (8 in.) long. 
 The wire may be cut with ordinary scissors. 
 
 (6) 20 c.c. dilute solution of the salts listed in (b) is required. 
 Prepare by dissolving 1 c.c. of the salt in 20 c.c. water. 
 
METALS AND SALTS 83 
 
 Heat, if necessary, but cool before using. Use a separate test 
 tube for each salt. Tin chloride will not dissolve clear in water 
 alone. Add, therefore, to its solution a few drops of hydro- 
 chloric acid. Use only 0.5 c.c. of silver nitrate and of mer- 
 curic chloride. Do not touch either of these two with the fingers. 
 Label each tube with the formula of the substance it contains 
 and also with the symbol of the metal ion formed when the 
 substance dissolves in water. Obtain this information from 
 the textbook. Put on the label, also, the color of the solution. 
 
 Place 10 c.c. of each of the solutions, omitting the copper 
 sulphate, in separate test tubes, and suspend in each a piece 
 of sheet copper so that 1 cm. (0.4 in.) of the metal is above the 
 surface. 
 
 In the same way, suspend a strip of zinc in another 10 c.c. 
 of each solution, omitting the zinc sulphate. Let stand. 
 After a time, withdraw the strips and examine them minutely 
 with a lens. Use the upper portion, which should not have 
 been wet with the liquid, for comparison. Be prepared for 
 the fact that finely divided metals reflect light differently and 
 present a very different appearance from the same metals in 
 compact polished condition. 
 
 What appears to have happened ? Is the deposit on the 
 copper the only product ? If not, what must be the second 
 product, in each case? Note carefully any changes in the 
 colors of the solutions. Do these changes confirm your con- 
 clusions ? State your results in a table of four columns, put- 
 ting in the first, the metal used, in the second, the substance 
 in solution, in the third, the deposit, and in the fourth, the 
 other product. Write an equation for each change, first in 
 the ordinary way. Then write the more simple equations 
 which describe the same changes in the light of the ionic 
 theory. 
 
84 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 60 
 IONIZED AND UN-IONIZED SOLUTIONS 
 
 Apparatus. Small test tubes, some of which must be dry. 
 
 Materials. Cupric chloride. Cobalt chloride. Cupric sulphate. 
 Cobalt sulphate. Alcohol (95 per cent). Solution of hydrogen chlo- 
 ride in toluene. Mossy zinc. Magnesium ribbon. Iron (small nail). 
 Marble fragments. 
 
 Method. See textbook, page 288. 
 
 Exercise unusual care to avoid waste of the cobalt salts. They are 
 expensive. The solution of hydrogen chloride in toluene is easily 
 made by passing the gas into toluene until the latter is saturated. 
 It should be kept in a tightly stoppered bottle. 
 
 (a) Dissolve 02 c.c. of cupric sulphate in 2 c.c. water. Do 
 the same with 0.2 c.c. cobalt sulphate and with 0.2 c.c. cobalt 
 chloride in different tubes. Note the colors of the liquids. 
 Other cupric and cobalt compounds in dilute water solution show 
 the same colors, respectively. What conclusion can be drawn 
 from this fact ? The solutions of cupric compounds (which all 
 have the same color) and the solutions of cobalt salts (which 
 all have the same color) are good conductors of the electric current. 
 What follows from this, regarding the condition of the salt ? 
 Does it confirm your conclusion drawn from the color ? 
 
 Dissolve 0.3 c.c. cobalt chloride in 3 c.c. alcohol. Do the 
 same, in a separate tube, with cupric chloride. Study the colors 
 of the liquids and compare them with the water solutions con- 
 taining the same metals. Does the color of cobalt chloride in 
 alcohol resemble the color of water solutions of cobalt salts ? 
 Has the alcohol solution of cupric chloride the same color as 
 cupric compounds dissolved in water ? What conclusion do 
 you deduce regarding the condition of the salts in the solutions ? 
 
 These alcoholic solutions are all nonconductors of the current. 
 Does this confirm your conclusion drawn from the colors? 
 Can you think of any method, based upon a study of the 
 boiling points of water and alcohol solutions, by which your 
 conclusions might be tested ? 
 
HYDROLYSIS 85 
 
 Pour half of the alcoholic solution of cupric chloride into 
 3 c.c. water in a small test tube. Result ? Do the same with 
 the alcohol solution of cupric chloride in another tube. Re- 
 sult ? What is indicated by the fact that the color changes and 
 the appearance of conductivity in the liquids are simultaneous ? 
 
 (6) Obtain, in a dry test tube, 5 c.c. of a solution of hydro- 
 gen chloride in toluene. Test the behavior of this liquid in 
 dry tes"t tubes with zinc, magnesium, iron (small nail), and a 
 bit of marble or calcite. Result ? Investigate the action of 
 ordinary hydrochloric acid on the same substances. Result? 
 
 The water solution of hydrogen chloride conducts the 
 electric current, but the toluene solution is a nonconductor. 
 Explain the connection between chemical activity and con- 
 ductivity. 
 
 EXERCISE 61 
 HYDROLYSIS 
 
 Apparatus. Reading glass or other long focus lens. Five small 
 test tubes. Glass rod. 
 
 Materials. (a) Cupric chloride (CuCl 2 ). Stannous chloride 
 (SnCl 2 ). Ferric chloride (FeCl 8 ). Cupric sulphate (CuSO 4 ). Alu- 
 minium sulphate (A1 2 (SO 4 ) 3 ). 
 
 Distilled water. Red and blue litmus paper. 
 
 (6) Sodium carbonate (Na 2 CO 3 ). Potassium carbonate (K 2 CO 3 ). 
 Sodium sulphide (Na 2 S). 
 
 (c) Sodium chloride (NaCl). Potassium chloride (KC1). Sodium 
 nitrate (NaNO 3 ). Potassium nitrate (KNO^). 
 
 Method. See textbook, page 289. 
 
 Take special care to have test tubes and glass rods used in this work 
 perfectly clean. 
 
 NOTE : Before doing the work, read up the subject of hydrolysis 
 in the textbook. In testing with litmus paper, put a small drop of 
 the liquid on the paper with a glass rod. Use the same paper for 
 many tests. In the interpretation of the results, remember that the 
 reddening of blue litmus is positive proof of the presence of an acid 
 7 
 
86 LABORATORY STUDIES IN CHEMISTRY 
 
 + 
 (that is, of hydrogen ions H), since nothing else can produce the 
 
 change in color. The turning blue of red litmus is proof of the pres- 
 ence of a base (that is, of hydro xyl ions OH) . Absence of effect on 
 both kinds of litmus shows, therefore, that neither acids nor bases 
 
 + 
 (H and OH ions) are present in measurable quantity. 
 
 (a) Dissolve 0.2 c.c. of each of the substances mentioned in 
 (a) in 10 c.c. distilled water in a small test tube. Use 'a sep- 
 arate tube for each substance. Heat until solution is complete. 
 Then cool in a stream of water. 
 
 (1) Are the liquids completely clear ? If the eye alone 
 does not detect evidence of the formation of a precipitate, a 
 very delicate test is to focus a beam of sunlight in the liquid 
 with a lens. The smallest traces of solid matter make the 
 path of the beam visible, on the same principle as the motes in 
 a sunbeam. Try this with each solution. Try it also with 
 the distilled water used, for comparison. 
 
 (2) Ascertain the action of each liquid upon red and blue 
 litmus paper. What is, in each case, the only acid which 
 could possibly be present? What, then, must be the other 
 product? Assuming that you detected evidence of the for- 
 mation of precipitates in (1), what is probably the nature of 
 the precipitate in each case ? Complete the following equa- 
 tions, supplying coefficients where they are denoted by letters : 
 
 CuCl 2 + *H 2 0^Cu(OH) 2 + ..., 
 
 SnCl 2 + xH 2 0^Sn (OH) 2 + -, 
 
 FeCls 4- xH 2 O^Fe(OH) 3 + -, 
 
 CuSO 4 -f *H 2 O;Cu(OH) 2 + ..., 
 
 A1 2 (SO 4 ) 8 + x H 2 O->?/ A1(OH) 8 + 
 
 The five substances in (a) are salts of active acids and in- 
 active bases. Explain what this statement means. Do your 
 results corroborate it ? 
 
 (&) Treat the substances mentioned in (6) in the same way. 
 Heating and the examination for suspended solid matter may 
 be omitted, since the acids and bases formed by hydrolysis of 
 
SEPARATION OF LEAD, SILVER, AND MERCURY 87 
 
 these three salts are all freely soluble. How do these sub- 
 stances differ from those in (a) ? What is the only base 
 which could possibly be present in each solution ? What, 
 then, must be the second product in each case ? These three 
 substances are salts of inactive acids with active bases. Ex- 
 plain the meaning of this statement and its bearing upon your 
 results. Complete the equations : 
 
 K 2 C0 3 + x H 2 ^ H 2 C0 3 
 
 (c) Investigate the four substances in (c) in the same way. 
 For the same reasons as in (6), the testing for separated solid 
 matter can be neglected. How does this class of substances 
 differ from the other two ? Is there reason for assuming any 
 interaction between the salts and water? These four sub- 
 stances are salts of active acids with active bases. What does 
 this mean and what bearing has it upon your results ? l 
 
 EXERCISE 62 2 
 SEPARATION OF LEAD, SILVER, AND MERCURY 
 
 Apparatus. Small test tubes. Beaker. Funnel. Glass rod. 
 Wire gauze. 
 
 Materials. Solutions of lead nitrate, silver nitrate, and mercu- 
 rous nitrate. Potassium chromate solution (1 : 20). Filters. Sheet 
 copper. Blue litmus paper. 
 
 Method. See textbook, page 233 (oable). 
 
 (a) (1) To 5 c.c. of lead nitrate solution in a small test 
 tube, add dilute hydrochloric acid until the action is complete. 
 Test this by shaking vigorously, letting the precipitate settle, 
 
 1 If the time allotted to the subject permits, a classroom discussion of 
 these phenomena from the standpoint of the ionization hypothesis would 
 be valuable. 
 
 2 With the usual laboratory period (ninety minutes) the teacher may 
 find it best to take up (a), (&), and (c) one week and (d) and (e) the next. 
 
88 LABORATORY STUDIES IN CHEMISTRY 
 
 and adding a drop or two of hydrochloric acid to the liquid. 
 Pour off the liquid as completely as you can without losing 
 the precipitate, fill the tube half full of cold water, shake, 
 and again pour off. What is removed by this treatment ? 
 
 (2) Dissolve the precipitate in the smallest possible quantity 
 of hot water. At once divide the solution into three equal 
 portions. Stand the first aside and examine it when cold. 
 Result ? To the second, add 2 c.c. of a solution of potassium 
 chromate. Result ? To the third, add 1 c.c. of sulphuric 
 acid. Result ? Complete the equations : 
 
 Pb(NO 3 ) 2 + zHCl -> PbCl 2 + ..., 
 PbCl 2 + K 2 Cr0 4 -+ PbCr0 4 + -, 
 PbCl 2 + H 2 S0 4 -> PbS0 4 + .... 
 
 (6) (1) Treat 5 c.c. silver nitrate solution exactly as in 
 (a) (1). 
 
 (2) Test the solubility of silver chloride in hot water. 
 Pour off the water and divide the precipitate into two portions. 
 Stand the first in the brightest light available for ten minutes. 
 Meanwhile, test the action of ammonia on the second portion. 
 Add dilute nitric acid to the ammonia solution until the odor 
 of ammonia disappears. Result? Complete the equation : 
 
 AgNO s + HCl-> AgCl + -.. 
 
 (c) Treat 5 c.c. of mercurous nitrate solution as in (a) (1). 
 Divide the precipitate into two portions. Does hot water dis- 
 solve mercurous chloride ? What effect has ammonia upon it ? 
 
 (d) Mix 5 c.c. each of the solutions of lead, silver, and mer- 
 curous nitrates. Add dilute hydrochloric acid until it forms 
 no further precipitate. Shake well and filter. Pour a little 
 cold water over the precipitate. Reject the filtrate. What 
 substances are contained in the precipitate ? 
 
 (1) Wash the precipitate with 50 c.c. boiling water, being sure 
 to reach every part of it. Preserve the liquid. Which of the 
 three chlorides does it contain ? Prove by using the test with 
 potassium chromate and that with sulphuric acid as in (a) (2). 
 
THE BEAD TESTS 89 
 
 (2) What substances are still on the filter ? Pour ammonia 
 over it. Which dissolves ? Receive the liquid in a clean test 
 tube and add dilute nitric acid to it until the ammonia is neu- 
 tralized (litmus paper). 
 
 (3) Which chloride has caused the darkening with ammonia? 
 Make a little aqua regia by pouring 1 c.c. hydrochloric acid (con- 
 centrated) into 0.5 c.c. concentrated nitric acid. Warm it and 
 pour it over the filter, receiving the filtrate in a clean test tube. 
 Dilute with 10 c.c. water and place a 1 X 2 cm. (0.4 X 0.8 in.) 
 piece of clean sheet copper in the liquid. Let stand. Wash, 
 rub with the finger, and examine. 
 
 (e) Ask for an unknown solution and analyze it for silver, 
 mercury, and lead, proceeding systematically as in (d). Note 
 that the metals must be separated from each other before the 
 tests can be applied. In writing your notes, remember that 
 to prove the absence of a substance is frequently just as im- 
 portant (e.g. in cases of suspected poisoning) as to prove its 
 presence. 
 
 EXERCISE 63 
 
 THE BEAD TESTS 1 
 
 Apparatus. Platinum wire (mounted in piece of glass rod) . Blow- 
 pipe. Wing top. 
 
 Materials. Borax powder. Microcosmic salt (sodium ammonium 
 phosphate). 
 
 (a) Cobalt nitrate. Nickel nitrate. Manganese dioxide. Chrome 
 alum. Copper sulphate. Ferric chloride. Sodium carbonate. 
 
 (6) Orthoclase (0.5 mm. fragment). 
 
 (c) Optional. Siderite, rhodonite, chrysocolla. 
 
 Method. See textbook, page 338. 
 
 Either the Bunsen burner or the blowpipe may serve as the source 
 of heat. If the burner is used, reduce the access of air until a small 
 yellow area appears in the upper portion of the flame. This luminous 
 area contains glowing carbon. It is called the reducing flame. The 
 
 1 Many teachers will prefer to inform the students beforehand what 
 colors will be obtained in the beads by correct work. 
 
90 LABORATORY STUDIES IN CHEMISTRY 
 
 strongest oxidizing flarne is the extreme upper part (blue), but any 
 part of the outer mantle can be used. Clamp the burner at an 
 angle of 25 with the vertical to avoid dropping substances into the 
 chimney. 
 
 If the blowpipe is employed, wash off the mouthpiece. Use the 
 wing top. Re-read the directions in Exercise 6. The reducing 
 flame is obtained by placing the tip of the blowpipe just inside of the 
 base of the edge of the flame and bending down the flame with a 
 gentle blast. It should be somewhat yellow and perfectly steady and 
 noiseless. It should surround the sample completely. In all blowpipe 
 work the air-holes at the base of the burner should be closed. 
 
 It is convenient to assign borax and microcosmic salt to different 
 groups of students. 
 
 Bend the end of the platinum wire into a circle 2 mm. (0.08 in.) 
 in diameter. Heat the loop red hot and dip it into powdered 
 borax. Notice the swelling up due to loss of water of crystal- 
 lization. Melt the anhydrous borax to a bead. Touch with 
 the hot bead a speck of cobalt nitrate not more than 0.5 mm. in 
 diameter. Return to the flame. When the bead appears clear, 
 let cool and examine. If the bead is opaque, too much cobalt 
 nitrate was used. Discard it and make another. Much more 
 rarely it happens that the color is pale and indistinct. In 
 that case, heat again and take up an additional speck of cobalt 
 nitrate. Use the oxidizing flame in melting the bead. Then 
 hold it persistently in the reducing flame and see whether the 
 color changes. 
 
 Remove the bead by heating it red hot and dipping into 
 water. The fragments can be detached from the wire without 
 difficulty. Make a fresh bead and remove it, to cleanse the 
 wire from cobalt, before proceeding to the next test. If the 
 third bead has a color, discard it also. A clean, colorless bead 
 should be used for each test. 
 
 In the same way, investigate the behavior of the substances 
 mentioned in (a), each time studying the behavior in both 
 flames. The result, with all except the last, is due to the 
 metal of the salt. Any other compounds of the same metals 
 would behave in the same way. In several cases, the bead 
 
THE BEAD TESTS 
 
 91 
 
 while hot (not red hot) has a different color from that which 
 it has when quite cold. Does sodium carbonate give any color 
 to the bead ? Notice the escape of carbon dioxide in this case. 
 This is the blowpipe test for a carbonate. 
 
 Record your results in a table thus : 
 
 NAME OF 
 COMPOUND 
 
 FOEMULA 
 
 COLOR OF BEAD 
 O.F. 1 
 
 COLOR OF BEAD 
 R.F.1 
 
 ; 
 
 
 Hot Cold 
 
 Hot Cold 
 
 (6) If there is time for it, the substances in (a) may be 
 tested in beads made with microcosmic salt, in exactly the 
 same way. 
 
 In any case, make, with a clean bead from microcosmic salt 
 and a 0.5 mm. bit of orthoclase, the test for a silicate. The in- 
 soluble residue which swims in the bead has the same compo- 
 sition as quartz (Si0 2 ). It is called the "silica-skeleton." 
 
 (c) is a suggested list of three minerals in which you are to 
 identify the metal by the borax bead color in oxidizing and 
 reducing flames. Also determine whether the substance is a 
 silicate or carbonate. 
 
 1 The abbreviations O.F. and R.F. are used for oxidizing flame and re- 
 ducing flame. 
 
92 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 64 ! 
 DYEING 
 
 Apparatus. Seven agate pans. Liter flask for roughly measuring 
 water. Glass rod. Trip scales. 
 
 Materials. Cotton cloth (white). Flannel (white). Congo red. 
 Aniline red. Malachite green. Distilled water. Sodium carbonate. 
 Sodium sulphate. Tannic acid. Tartar emetic. Large gummed 
 labels (Dennison's, No. 201). Paste. 
 
 Method. See textbook, page 234. 
 
 Preparation of the cloth. Cut into strips 4x2 cm. (1.6 X 
 0.8 in.). Each student will need 2 pieces of the flannel and 5 
 of the cotton. The sizing must be removed from the cotton 
 by boiling it in an agate pan with a mixture of 40 c.c. concen- 
 trated hydrochloric acid and 1 liter tap water, rinsing under 
 the hydrant and then dipping in a cold mixture of 10 c.c. am- 
 monia and 1 liter tap water. This treatment is not necessary 
 with the flannel. 
 
 B 
 
 Prepare the following baths : 
 
 (1) 1 gram Congo red is dissolved by stirring in 1 liter of 
 distilled water in an agate pan. Add 1 gram sodium carbon- 
 ate and 2 grams sodium sulphate. 
 
 (2) 0.5 gram aniline red in 1 liter distilled water. 
 
 (3) 0.5 gram malachite green in 1 liter distilled water. 
 
 (4) 1 gram tannic acid in 1 liter distilled water. 
 
 (5) 1 gram tartar emetic in 1 liter distilled water. 
 
 (1), (2), (3), and (4) are heated to gentle boiling. (5) should 
 be cold. Each pan should be plainly labeled with its number. 
 
 1 In order to finish in a laboratory period, it will be necessary to dis- 
 tribute the preparation of the baths to different students. 
 
DYEING 93 
 
 (a) Wet a strip of cotton cloth, place it in (1) (gentle boil- 
 ing), and move it about with a glass rod for one minute. Re- 
 move and wash well under the tap. Congo red belongs to the 
 class of dyes which dye cotton without a mordant. Fasten the 
 dyed cloth to your notebook page. 
 
 (6) Place a second strip of cotton cloth in (2) and a third in 
 (3) for one minute. Eemove and wash well. Eesult ? Aniline 
 red and malachite green are examples of a great class of dye- 
 stuffs which do not give fast colors on cotton without the use 
 of a mordant. 
 
 (c) Boil two strips of cotton cloth in (4) for five minutes. 
 Wring out and keep in motion in (5) for five minutes. Now 
 place one strip in (2) and move about constantly for one min- 
 ute. Treat the other similarly in (3). Try to wash out the 
 color. Eesult ? What part is played by the mordant (4 and 5) ? 
 Mount the dyed cloth on your notebook page. 
 
 (d) Stir a strip of flannel in (2) and a second in (3) for one 
 minute, without mordanting. Eemove and try to wash out the 
 color. What difference do you discover in the action of wool 
 and of cotton toward dyes of the class to which aniline red and 
 malachite green belong ? Mount the dyed cloth on the note- 
 book page. 
 
 Thoroughly wash the pans, using a little concentrated 
 hydrochloric acid, if necessary, to remove the dyestuff. 
 
94 
 
 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 65 
 
 NITRIC ACID, AQUA REGIA 
 
 Apparatus. Retort (150 c.c.) with glass stopper. Agate pan. 
 Beaker. Small test tubes. Trip scales. Glass rod. Mortar and 
 pestle. Manila paper. 
 
 Materials. Sodium nitrate. Mossy zinc. Magnesium ribbon. 
 Iron filings. Tin foil. Colored cloth of any kind. Gold leaf. Fer- 
 rous sulphate. Manila paper. 
 
 Method. See textbook, page 297. 
 
 CAUTION: The gases given off ivhen nitric acid acts upon metals 
 and the vapor of nitric acid itself are poisonous and must not be inhaled. 
 Do not get nitric acid upon the skin or clothing. 
 
 (a) 1 Fit up the apparatus shown in Fig. 21. Roughly weigh 
 on the trip scales enough sodium nitrate to fill the retort about 
 
 one third. Weigh off 
 in a beaker an equal 
 quantity of concen- 
 trated sulphuric acid. 
 Introduce the sodium 
 nitrate into the retort 
 by means of a piece 
 of paper. Add the 
 sulphuric acid, insert 
 the glass stopper (not 
 a rubber or wooden 
 cork, which would be 
 rapidly destroyed by 
 the nitric acid), and 
 heat gently. Only 
 FIG. 21. vapor, not solid or 
 
 liquid, must pass over. 
 Why ? Empty the liquid which remains in the retort into the 
 
 1 If the period is short, it may be necessary to omit or to postpone (&) 
 and (c). 
 
NITRIC ACID, AQUA REGIA 95 
 
 vessel provided for the purpose. (Care!} When the retort is 
 cold, half fill it with water and boil gently to clean it. 
 
 Examine the nitric acid which collects and record its prop- 
 erties. Use the nitric acid in the following experiments. 
 Cover a piece of zinc with water in a test tube and slowly add 
 nitric acid. Do the same thing with a little iron filings and a 
 piece of magnesium. In these reactions water is produced, to- 
 gether with the nitrate of the metal used. The gas produced 
 may be nitrous oxide, nitric oxide, or nitrogen peroxide, accord- 
 ing to the temperature and strength of the acid. Do not try to 
 write the equations, which are quite difficult. Simply remem- 
 ber the general character of the action and the way in which it 
 differs from the action of sulphuric or hydrochloric acid on the 
 same metals (see textbook, page 298). 
 
 Drop a fragment of tin into concentrated nitric acid in a test 
 tube. The metal is converted into tin oxide by the oxygen of 
 the nitric acid. Let a drop of nitric acid fall upon a colored 
 fabric of any kind. 
 
 (b) Aqua regia. Pick up a small piece of gold leaf with the 
 end of a wet glass rod, and rinse it into a test tube with water. 
 In the same way place another piece of gold leaf in another 
 test tube. Add to one tube nitric acid and to the other hydro- 
 chloric acid. Heat both tubes. Does the gold dissolve ? Pour 
 the contents of either tube into the other, and go on heat- 
 ing. (?) The product is gold chloride, and the gold dissolves 
 because the oxygen of the nitric acid liberates chlorine from 
 the hydrochloric acid and the chlorine attacks the gold. The 
 mixture of nitric and hydrochloric acids will also dissolve 
 platinum. 
 
 (c) Test for nitric acid or a nitrate (N0 3 ions). Exercise 
 unusual care in following directions. Select 2 c.c. of clean 
 ferrous sulphate crystals, wash in running water, dry with 
 paper (manila), and powder in a clean mortar. Shake the pow- 
 der with 10 c.c. water (no heat) until you have a strong 
 solution. 
 
 Place 3 c.c. of the clear liquid in a small test tube, incline 
 
96 LABORATORY STUDIES IN CHEMISTRY 
 
 the tube at an angle of 45, and allow 5 c.c. strong sulphuric 
 acid to trickle slowly down the side. Avoid shaking. Being 
 denser, the acid will form a layer below the solution. 
 
 Now, add in the same way, a few drops of nitric acid which 
 has been diluted with twenty times its volume of water, 
 Eesult? 
 
 Repeat, using a few drops of sodium nitrate solution about 
 1:20. 
 
 If time permits, repeat, using other nitrates (e.g. potassium 
 nitrate, ammonium nitrate) to show that the test is for NO 3 
 ions in general, not for any special nitrate. 
 
 / 
 
 EXERCISE 66 
 
 POTASSIUM NITRATE 
 
 Apparatus. Evaporating dish. Glass plate. Funnel. Beaker. 
 Lens. Wire gauze. Trip scales. Glass rod. Graduated cylinder. 
 
 Materials. Sodium nitrate. Potassium chloride. Potassium 
 nitrate crystals. Silver nitrate solution. Distilled water. Filters. 
 
 Method. See textbook, page 301. 
 
 Place in a dish 25 c.c. water. Add 12 grams sodium nitrate 
 and 11 grams potassium chloride. Heat on wire gauze, stirring 
 with a glass rod until both are completely dissolved. 
 
 Stir gently and continue heating until half the water has 
 evaporated (small flame). Pour off the clear liquid into a 
 beaker and let it stand until cool. Meanwhile, scrape the 
 crystals left in the dish into a filter supported in a funnel. 
 Press carefully with the rod so as to squeeze out as much of 
 the liquid as possible. Put a few crystals on a glass plate 
 and examine with a lens or low-power microscope. What is 
 the form ? Only four substances might be obtained from your 
 solution in this way. What are they? Which of them do 
 you know to crystallize in the form you have observed (text- 
 book, page 206). Taste the crystals (a trace only), Does the 
 taste confirm your opinion ? 
 
PREPARATION OF SODIUM NITRITE 97 
 
 Examine the crystals which, have separated in the beaker 
 and treat them in the same way. Compare them with the 
 crystals of potassium nitrate in the stock bottle. Use the lens 
 or, if necessary, the microscope. 
 
 Look up the solubility curves of sodium chloride and of 
 potassium nitrate at different temperatures (textbook, page 
 207). 
 
 Why did the sodium chloride separate while the liquid was 
 hot ? Why did the potassium nitrate remain dissolved until 
 the liquid cooled ? 
 
 Does your potassium nitrate contain any sodium chloride as 
 an impurity (look again at the solubility curve for sodium 
 chloride)? Verify your prediction by dissolving 0.5 c.c. of 
 your potassium nitrate in distilled water and testing the solu- 
 tion for chloride with one drop of silver nitrate solution. 
 Eeserve. Dissolve the rest of your potassium nitrate in 10 c.c. 
 hot water and allow the solution to cool and crystallize. Test 
 again with silver nitrate. Is the second crop of crystals purer 
 than the first ? Why ? 
 
 EXERCISE 67 
 PREPARATION OF SODIUM NITRITE 
 
 Apparatus. Iron dish. Beaker. Evaporating dish. Funnel. 
 Glass rod. Two small test tubes. Trip scales. 
 
 Materials. Sodium nitrate. Lead foil or test lead. Filters. 
 Method. See textbook, page 305. 
 
 Melt 10 grams sodium nitrate in an iron dish and heat it 
 strongly (take special care not to spill any of the melted sub- 
 stance upon the table, since it would burn deeply into the 
 wood). Add gradually 20 grams of test lead (granulated) or 
 the same weight of lead foil cut into small pieces. Stir with 
 a glass rod and continue heating and stirring until the metal 
 has almost completely disappeared. Let cool. 
 
 Meanwhile, boil 30 c.c. of water in a beaker and pour it 
 
98 LABORATORY STUDIES IN CHEMISTRY 
 
 upon the cold substance in the iron dish. Boil for a short 
 time and filter, receiving the filtrate in a porcelain dish. 
 Evaporate carefully to small volume and let it crystallize. 
 The product is sodium nitrite. 
 
 Compare it with sodium nitrate. Is there any difference in 
 color? Dissolve 1 c.c. of each in 5 c.c. water and cautiously 
 add 1 c.c. strong sulphuric acid. Results ? 
 
 What is the purpose of adding the lead ? What substance 
 remained on the filter ? 
 
 EXERCISE 68 * 
 NITRIC OXIDE 
 
 Apparatus. Gas-generating bottle with thistle tube and delivery 
 tube. Test tube. Agate pan. Iron spoon. Three bottles. Glass plates or 
 filter paper for covering bottles. Watch glass. Beaker. Wire gauze. 
 
 Materials. Copper clippings (No. 12 wire cut into 1 cm. pieces is 
 suitable). Iron wire. Candles. Sulphur. Red phosphorus. Asbes- 
 tos paper. 
 
 Method. See textbook, pages 298, 299, 304. 
 
 CAUTION: Nitric oxide is poisonous. Keep the bottles of the gas 
 covered during combustions and let the products escape out of the windows. 
 
 Nitric oxide is made in the same apparatus which is used 
 for generating hydrogen. Fill the generator to the depth of 
 about 1 cm. with copper clippings or cut pieces of sheet cop- 
 per. In another bottle, dilute 50 c.c. nitric acid with twice its 
 volume of water. Cool this liquid and pour it upon the copper 
 until the generator is one third filled. Make sure that the 
 thistle tube dips into the liquid. Collect the gas over water. 
 It is well to stand the generator in cold water. If the 
 evolution of gas becomes too energetic, pour a little water 
 down the thistle tube. Collect three bottles and one test tube 
 of the gas. Then stop, as even the first gas which comes off is 
 not quite pure and the later portions contain large quantities 
 
 1 Two students can work together to advantage. 
 
NITROUS OXIDE 99 
 
 of nitrous oxide and other impurities. Leave the bottles stand- 
 ing in the water. 
 
 Disconnect the apparatus (do not inhale the gas) and pour a 
 little of the blue liquid into a watch glass. Use the watch 
 glass as a cover for a beaker half filled with water kept gently 
 boiling. Let the blue liquid' evaporate almost to dryness. 
 What is the product ? Wash off the copper in the generator 
 and return what is left of it to the stock bottle. 
 
 Use the test tube of the gas to investigate its solubility in 
 water. Expose a bottle of nitric oxide to the air. Eesult ? 
 
 Slip aside the cover of a bottle and plunge to the bottom of 
 the bottle some sulphur burning vigorously in a spoon lined 
 with asbestos paper. Remove the sulphur at once, keeping 
 the bottle covered, and do the same thing with a lighted can- 
 dle. Why should the candle be placed in the bottom of the 
 bottle ? Interpret the results. 
 
 Reline the spoon, fill it with red phosphorus, ignite, and 
 plunge into a bottle of the gas. Result ? Before putting 
 away the spoon, heat it to redness to burn out any unused 
 phosphorus. 
 
 EXERCISE 69 * 
 NITROUS OXIDE 
 
 Apparatus. Large test tube with rubber stopper and delivery 
 tube, connected as shown in cut. Four bottles. Two small test 
 tubes. Agate pan. Iron spoon. Glass plates or filter paper for 
 covering bottles. 
 
 Materials. Ammonium nitrate. Christmas-tree candles. Iron 
 wire. Sulphur. Red phosphorus. Wooden splints. Asbestos paper. 
 
 Method. See textbook, page 303. 
 
 Fill a large test tube one third with ammonium nitrate. 
 Clamp it at an angle of 45, and insert a perforated stopper 
 with a delivery tube. It is advisable, though not absolutely 
 
 1 Two students can work together to advantage. 
 
100 LABORATORY STUDIES IN CHEMISTRY 
 
 necessary, to pass the gas through an empty large test tube 
 closed by a doubly perforated stopper before collecting it. 
 
 The apparatus is 
 shown in Fig. 22. 
 Apply a gentle heat 
 and collect the gas 
 over warm water. 
 The evolution of gas 
 must be slow a 
 bubble or two a sec- 
 ond. If it becomes 
 too rapid, explosions 
 result. This can be 
 easily controlled by 
 lowering or remov- 
 
 FlG 22 i n S the flame. Stop 
 
 heating and remove 
 
 the stopper before the ammonium nitrate is exhausted. Ex- 
 plosions sometimes occur when the quantity of substance becomes 
 small. If the ammonium nitrate shows signs of giving out be- 
 fore you have enough gas, disconnect, add more ammonium 
 nitrate directly to the liquid in the test tube, and resume heat- 
 ing cautiously. Is there evidence of the formation of any 
 product besides the gas ? What ? 
 
 Collect four bottles and two test tubes full of the gas. Cover 
 the bottles with glass plates or wet filter paper, and stand 
 them upright on the desk. Use one bottle to determine color, 
 odor, and taste. Try the spark test in the test tube. Ascer- 
 tain if the gas is soluble in water. Plunge a lighted candle 
 into a bottle of it. Result? Set fire to some sulphur in a 
 deflagration spoon lined with asbestos paper, and at the instant 
 the sulphur begins to burn plunge it into the third bottle of 
 nitrous oxide. It should be extinguished. Cover the bottle, 
 and heat the sulphur until it burns vigorously. Plunge it 
 again into the gas. Result ? Is nitrous oxide easy or diffi- 
 cult to decompose into its elements ? Which has probably 
 
PHOSPHATE FERTILIZERS? ;' j , J': ;*, ; \ # 
 
 the higher temperature, the candle flame or the flame of burn- 
 ing sulphur? Remove the asbestos and reline the spoon. 
 Fill it with red phosphorus, ignite, and plunge into a bottle of 
 the gas. Result ? 
 
 EXERCISE 70 
 PHOSPHATE FERTILIZERS 
 
 Apparatus. Porcelain dish. Small test tubes. Glass rod. Funnel. 
 
 Materials. Sodium hydrogen phosphate (Na 2 HPO 4 ). Ammo- 
 nium nitrate. Ammonium molybdate solution. Apatite or phos- 
 phate rock. Commercial superphosphate. Filters. 
 
 Method. See textbook, page 331. 
 
 (a) Dissolve in a small test tube 0.5 c.c. sodium hydrogen 
 phosphate and 1 c.c. ammonium nitrate in 5 c.c. water, and add 
 five drops of nitric acid. Add 2 c.c. ammonium molybdate 
 solution and warm gently, not to boiling. Result? The 
 composition of the product depends upon the temperature, so 
 that no formula can be assigned to it. 
 
 This is the test for phosphoric acid, or a soluble phosphate 
 
 (that is, for PO^ions). 
 
 (b) Place 10 grams powdered apatite or phosphate rock in a 
 dish and add 4 c.c. water and 4 c.c. concentrated sulphuric 
 acid. Warm for ten minutes, stirring with a glass rod. Add 
 10 c.c. water, warm, filter, and test the clear liquid as in (a), 
 omitting the sodium hydrogen phosphate. Has the action of 
 the sulphuric acid on the mineral produced a soluble phos- 
 phate ? Explain (see textbook, p. 331).* 
 
 (c) Clean the dish, place 2 c.c. superphosphate in it, add 
 50 c.c. water, and boil. Filter and test as in (6). Result? 
 Does the fertilizer contain a soluble phosphate ? What is the 
 object of the sulphuric acid in its manufacture ? 
 
102 L/IB^RATGRY STUDIES IN CHEMISTRY 
 
 EXERCISE 71 l 
 
 POTASSIUM CHROMATE AND POTASSIUM 
 DICHROMATE 
 
 Apparatus. Graduated 100 c.c. cylinder. Trip scales. Beaker. 
 Evaporating dish. Three small test tubes. 
 
 Materials. Potassium hydroxide. Potassium dichromate. Potas- 
 sium chromate. Dilute solutions of barium chloride, lead nitrate and 
 silver nitrate. The potassium dichromate should be powdered to 
 hasten solution. 
 
 Method. See textbook, pages 342 and 343. 
 
 (a) Calculate the molecular weight of potassium dichromate. 
 Using decigrams as your unit, weigh off one fourth of the 
 molecular weight and dissolve it in 50 c.c. water in a dish, 
 using gentle heat, if necessary. From the equation 
 
 K 2 Cr 2 O 7 +2KOH-> 2 K 2 CrO 4 + H 2 O, 
 
 (Potassium dichromate) (Potassium chromate) 
 
 calculate the quantity of potassium hydroxide which would be 
 required to interact with the potassium dichromate. Weigh 
 off this quantity, dissolve it in 10 c.c. water, and add it to the 
 solution of the dichromate. What does the color change indi- 
 cate ? 
 
 Estimate roughly how far the solution must be evaporated 
 in order to deposit three fourths of its potassium chromate on 
 cooling. Calculate the quantity of potassium chromate from 
 the equation above. Assume that 1 c.c. water dissolves two 
 thirds of a gram of potassium chromate at room temperature. 
 
 Evaporate the solution as far as you think it is necessary 
 and let it cool. Meanwhile, go on with (c). If you do not ob- 
 tain a good crop of crystals, evaporate further and find the 
 error in your calculation. Examine the crystals and compare 
 them with potassium dichromate. 
 
 1 If the laboratory period is short, two students can work together to 
 advantage. 
 
POTASSIUM CHROMATE 103 
 
 * 
 
 (6) l Your dish must contain one half the molecular weight 
 of potassium chromate, measured in decigrams. Why ? Cal- 
 culate the quantity of sulphuric acid required to interact with 
 this according to the equation : 
 
 2 K 2 CrO 4 + H 2 SO 4 >- K 2 Cr 2 O 7 + K 2 SO 4 + H 2 O. 
 
 Dissolve the potassium chromate in 50 c.c. water and slowly 
 add the calculated quantity of sulphuric acid, stirring. What 
 does the change in color indicate ? If 8 parts water dis- 
 solve 1 part potassium dichromate at room temperature, how 
 far must you evaporate in order to allow three fourths of 
 the substance to crystallize on cooling ? To answer this, you 
 must know the amount of potassium dichromate in the liquid. 
 Is it necessary to calculate this ? Why ? Evaporate to the 
 volume estimated and let the solution crystallize. 
 
 (c) Dissolve 1 c.c. potassium dichromate in 20 c.c. water. 
 In three separate test tubes (small), investigate the behavior of 
 the solution with solutions of barium chloride, lead nitrate, and 
 silver nitrate. Use not more than 5 c.c. of each solution. 
 
 The precipitates are the chromates of the corresponding 
 metals. Record their properties and see whether they dis- 
 solve in nitric acid. 
 
 1 If the laboratory period is short, (6) can be assigned to a second stu- 
 dent and started simultaneously with (a). Use one half the molecular 
 weight of potassium chromate, taking decigrams as the unit. 
 
104 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 72 
 AMMONIUM BICHROMATE 
 
 Apparatus. Four small test tubes, one of which must be dry. 
 Glass rod. 
 
 Materials. Solid ammonium dichromate (NH 4 ) 2 Cr 2 O 7 . Solutions 
 of barium chloride, lead nitrate and silver nitrate. Potassium hydrox- 
 ide solution. Red litmus paper. 
 
 Method. The chemical behavior of a substance when ionized and when 
 not ionized is very different. 
 
 (a) Repeat (c) of the preceding exercise, using ammonium 
 dichromate instead of the potassium salt. 
 
 To 5 c.c. ammonium dichromate solution add ammonium 
 hydroxide until the color change is complete. Does it behave 
 like potassium dichromate ? What must have been formed ? 
 Equation ? 
 
 (6) To 5 c.c. ammonium dichromate solution add potassium 
 hydroxide solution until the color is pure yellow. Then add 
 as much more potassium hydroxide and heat gently. Note 
 odor. Test the gas with red litmus paper. With a rod wet 
 with concentrated hydrochloric acid. What is it ? 
 
 Ammonium dichromate in water solution is largely ionized 
 
 to NH 4 , NH 4 , and Cr 2 6 7 . Accordingly, like other salts it 
 yields two classes of reactions, those of the ion NH 4 , of which 
 (6) is an example ; and those of the ion Gr/) ri of which various 
 examples are met in (a). 
 
 (c) Now investigate the conduct of the un-ionized substance. 
 Place 1 c.c. of the crystals in a dry test tube and heat gently. 
 Stop heating when the action begins, but resume heating, if 
 necessary, to complete it. Hold the tube with a paper holder 
 or a clamp. The chief products are nitrogen, water (steam), 
 and chromic oxide (solid). 
 
 (NH 4 ) 2 Cr 2 7 -> Cr 2 3 + 4 H 2 O + N 2 . 
 
 Note that this decomposition is totally different from the 
 reactions of the same substance in water solution. In the 
 
CHROMIUM IN AMMONIUM BICHROMATE 105 
 
 latter case it behaves as though the NH 4 and Cr 2 7 had parted 
 company and gives a different set of reactions for each, much 
 as a solution containing both copper and silver ions will give 
 the tests for both metals. In (c) there is no evidence of this 
 separation. The formation of water indicates, for instance, 
 that the hydrogen and the oxygen are in the same molecule. 
 Examine the chromic oxide carefully and test its solubility 
 in hydrochloric acid. 
 
 EXERCISE 73 
 
 THE PERCENTAGE OF CHROMIUM IN 
 AMMONIUM BICHROMATE 
 
 (Quantitative) 
 
 Apparatus. Porcelain crucible and cover. Pipestem triangle. 
 Balance. 
 
 Material. Ammonium dichromate. 
 
 Method. When ammonium dichromate is heated, the following 
 change occurs : 
 
 (NH 4 ) 2 Cr 2 O 7 -> Cr 2 O3 + N 2 + 4 H 2 O. 
 
 (Ammonium dichromate) (Chromic oxide) 
 
 The percentage of chromium in the sample can be calculated from 
 the weight of the chromic oxide left in the crucible. 
 
 Clean and weigh crucible and cover. Place cover on balance 
 pan beside crucible and weigh in the crucible 0.5 gram am- 
 monium dichromate. Cover crucible, place it on the triangle, 
 and heat cautiously with a small flame kept in motion. Hold 
 down the lid for the first few minutes by placing the tip of 
 your pencil through the ring. If any noise is heard or any 
 smoke appears, stop heating for a moment until quiet is 
 restored. Finally remove pencil and apply the full heat of 
 the burner for ten minutes ; cool and weigh without removing 
 cover. 
 
106 LABORATORY STUDIES IN CHEMISTRY 
 
 V 
 
 Calculation. The weight of the chromium in your sample is 
 obtained by working out the following fraction : 
 
 weigh chromic oxide x twice the atomic weight chromium 
 molecular weight chromic oxide 
 
 The percentage of chromium is : 
 
 weight chromium x 100 
 0.5 
 
 EXERCISE 74 
 
 THE PERCENTAGE OF IRON IN FERROUS 
 
 AMMONIUM SULPHATE 
 
 [FeS0 4 (NH 4 ) 2 S04 6 H 2 O] 
 
 (Quantitative) 
 
 Apparatus. Burette. Beaker. Stirring rod (thin, 3 mm. diam- 
 eter. Thick rods cause breakage of beakers). Graduated cylinder. 
 Balance. 
 
 Materials. Ferrous ammonium sulphate. Distilled water. A 
 solution of potassium permanganate, KMnO4, of such strength that 
 1 c.c. corresponds to 0.01 gram of iron. This solution is made by 
 dissolving 5.643 grams of potassium permanganate in water and 
 diluting the solution to 1 liter in a flask with a mark on the neck. 
 The student can prepare the solution by dissolving 0.564 gram of 
 potassium permanganate in 50 c.c. distilled water in a beaker. Make 
 sure that the permanganate is completely dissolved. Pour into a gradu- 
 ated cylinder, and wash the beaker with 5 c.c. distilled water, which 
 is poured into the cylinder. Repeat the washing three times. Dilute 
 with distilled water to exactly 100 c.c. and mix thoroughly. 
 
 Method. In presence of sulphuric acid, potassium permanganate 
 converts ferrous sulphate, FeSO 4 , into ferric sulphate, Fe 2 (SO4)3, 
 thus : 
 
 10 FeSO 4 + 2 KMnO 4 + 8 H 2 SO 4 -> 5 Fe 2 (SO 4 ) 3 -t- K 2 SO 4 
 
 Weigh in a dry, clean beaker 2 grams of ferrous ammonium 
 sulphate, half fill the beaker with distilled water, and stir until 
 
SODIUM CHLORIDE 107 
 
 the solid is completely dissolved. Do not heat. Add 3 c.c. con- 
 centrated sulphuric acid. 
 
 Fill the burette to zero with the permanganate and stand the 
 beaker on a piece of white paper. Slowly run in the perman- 
 ganate, stirring constantly. When the purple color seems to 
 spread through the liquid in the beaker before disappearing, 
 you are near the end, and the permanganate should be added 
 one drop at a time ; stirring after each. The first perceptible 
 color which remains after stirring a few seconds indicates 
 that the change is complete. If in doubt, record the reading 
 and add another drop. If the color becomes more intense, the 
 previous reading was the end. 
 
 Calculation. The reading of the burette x 0.01 = weight of iron 
 in sample. 
 
 weight of iron in sample x 100 
 
 2 2 = percentage of iron. 
 
 EXERCISE 75 
 
 DETERMINATION OF THE PERCENTAGE OF 
 CHLORINE IN SODIUM CHLORIDE 
 
 (Quantitative) 
 
 Apparatus. Burette. Small test tubes. Beaker. Stirring rod 
 (thin, 3 mm. diameter). Balance. 
 
 Materials. Pure sodium chloride. Decinormal (one-tenth normal) 
 silver nitrate solution (made by dissolving 17 grams silver nitrate in 
 distilled water and diluting to 1 liter in a volumetric flask). The 
 student can prepare the solution by dissolving exactly 1.7 gram of 
 silver nitrate in distilled water in a graduated cylinder, diluting to 
 100 c.c. and mixing thoroughly. Solution of potassium chromate 
 (20 grams) in distilled water (1 liter). Potassium chloride and 
 potassium bromide are optional. 
 
 Method. Dissolve a crystal of sodium chloride in 5 c.c. distilled 
 water in a clean test tube and add a few drops of silver nitrate solu- 
 tion. In another tube, mix 1 c.c. of silver nitrate solution with 1 c.c. 
 
108 LABORATORY STUDIES IN CHEMISTRY 
 
 of potassium chromate solution. The red precipitate is silver chro- 
 mate : 
 
 2 AgNO 3 + K 2 Cr0 4 -> Ag 2 CrO 4 + 2 KNO 3 . 
 
 Now when silver nitrate solution is dropped into a liquid containing 
 both sodium chloride and potassium chromate, silver chloride only is 
 formed as long as any chlorine ions remain. When the chlorine ions 
 are all converted into silver chloride, the first drop of silver nitrate in 
 excess gives the red color of silver chromate. 
 
 Weigh 0.2 gram of sodium chloride in a clean, dry beaker, 
 dissolve in 50 c.c. distilled water, and add 2 c.c. potassium 
 chromate solution. Fill the burette to zero with the silver 
 nitrate. Stand the beaker on white paper and slowly run in 
 the silver nitrate solution, stirring constantly. The first faint 
 permanent change in color is the end. When in doubt, record 
 the reading and add another drop. 
 
 Calculation. 
 
 1 c.c. decinormal silver nitrate = 0.00355 gram chlorine. 
 and, hence, burette reading x 0.00355 = weight of chlorine in sample ; 
 
 burette reading x 0.00355x100 = t of chlorine . 
 
 0.2 
 
 In the same way, determine the chlorine in potassium 
 chloride, taking 0.3 gram. 
 
 In the same way, determine the bromine in potassium 
 bromide, taking 0.4 gram. 
 
 1 c.c. decinormal silver nitrate = 0.008 gram bromine. 
 
ANALYSIS OF A SILVER COIN 109 
 
 EXERCISE 76 
 
 ANALYSIS OF A SILVER COIN 
 
 (Quantitative) 
 
 Apparatus. Balance. Burette. Graduated cylinder. Beaker. 
 Thin stirring rod. Watch glass. Test tubes. Tinner's shears. 
 
 Materials. Silver nitrate. Silver nitrate solution. Ammonium 
 sulphocyanide (NH 4 CNS). Solution of ferric ammonium sulphate 
 (Fe 2 (SO 4 ) 3 (NH 4 ) 2 SO 4 24H 2 O), twenty grams to about 1 liter of 
 distilled water. Distilled water. 
 
 Method. Dissolve a crystal of ammonium sulphocyanide in 10 c.c. 
 distilled water and divide the solution in two portions. To one por- 
 tion add a few drops of silver nitrate. The white precipitate is silver 
 sulphocyanide : 
 
 AgN0 3 + NH 4 CNS -> AgCNS + NH 4 NO 3 . 
 
 To the other portion add a few drops of ferric ammonium sulphate. 
 The red color is due to ferric sulphocyanide, formed from the ferric 
 sulphate and the ammonium sulphocyanide : 
 
 Fe 2 (S0 4 ) 3 + 6 NH 4 CNS -> 2 Fe(CNS), + 3 (NH 4 ) 2 SO 4 . 
 
 (Ferric sulphate) (Ferric sulphocyanide) 
 
 Now when ammonium sulphocyanide is added slowly to a liquid con- 
 taining both silver nitrate and ferric sulphate, silver sulphocyanide 
 only is formed until the silver is all precipitated and then the first drop 
 of ammonium sulphocyanide in excess gives the liquid the red color of 
 ferric sulphocyanide and indicates that the end has been reached. 
 
 In a graduated cylinder, dissolve 0.7 grain ammonium sul- 
 phocyanide in 100 c.c. distilled water and mix thoroughly. 
 0.315 gram of pure silver nitrate contaftis just 0.2 gram silver. 
 Weigh off this quantity of silver nitrate in a clean, dry beaker, 
 dissolve it in 50 c.c. distilled water, add 1 c.c. nitric acid and 
 1 c.c. ferric ammonium sulphate solution. 1 Fill the burette to 
 zero with the sulphocyanide solution, stand the beaker on 
 
 1 If the laboratory period is short, the instructor may prefer to prepare 
 a large quantity of the sulphocyanide solution and standardize it before- 
 hand. The experiment then requires only about 30 minutes. 
 
110 LABORATORY STUDIES IN CHEMISTRY 
 
 white paper, and allow the sulphocyanide to run in until the 
 color change occurs. Stir constantly and add the sulphocyanide 
 in small quantities. Endeavor to hit the first perceptible 
 change. When in doubt, take the reading and add another 
 drop. Plainly : 
 
 o P 
 
 ~ = weight of silver corresponding to 1 c.c. of your 
 
 sulphocyanide. 
 
 Take about one tenth of a dime for the analysis. The coin can 
 be easily cut with tinner's shears. Weigh the bit of coin accu- 
 rately, place in a beaker, and add 2 c.c. distilled water and 
 2 c.c. nitric acid. Cover with a watch glass, place on wire 
 gauze and put a small flame underneath. 
 
 When the coin is dissolved, add 50 c.c. distilled water and 
 1 c.c. ferric ammonium sulphate solution. 
 
 Fill the burette to zero with the sulphocyanide and proceed 
 exactly as you did in standardizing your solution. 
 
 Calculation. 
 
 burette reading x silver value of solution x 100 _ cent of si j ver 
 weight of sample ^ coin> 
 
 EXERCISE 77 
 
 THE ATOMIC WEIGHT OF COPPER BY REDUCING 
 CUPRIC OXIDE 
 
 (Quantitative) 
 
 Apparatus. Hard glass test tube about 10 x 1.2 cm. (4 x 0.5 in.) . 
 Glass tube about 20 cm. (8 in.) long. Rubber tubing for connecting 
 glass tube to gas supply. Balance., 
 
 Material. Cupric oxide (this should have been heated to redness 
 and placed in a stoppered bottle). 
 
 Method. Cupric oxide when heated in hydrogen or illuminating 
 gas is converted into copper : 
 
 The atomic weight of copper is obtained from the loss in weight. 
 
ATOMIC WEIGHT OF COPPER 
 
 111 
 
 The hard glass tube must be clean and dry. Weigh it accu- 
 rately. Cut a strip of paper 20x1 cm. (8x0.4 in.) and crease 
 it in the middle to make a V-shaped trough. Use this to intro- 
 duce the cupric oxide. Avoid getting the latter on the sides of 
 the tube. Weigh in the tube about 1 gram of cupric oxide. It 
 is not necessary to take exactly 1 gram, but whatever quantity 
 you take must be accurately weighed. 
 
 Connect the glass tube by means of the rubber tube to the 
 illuminating gas supply and, after lighting the gas, turn it 
 down till you have a flame about 15 mm. (0.5 in.) high. Blow 
 out the gas and set up the apparatus as shown in cut (Fig. 23). 
 Place the clamp 2 cm. (0.8 in.) 
 from the mouth of the tube so 
 that you may heat the cupric 
 oxide without burning the 
 clamp. Light the gas at the 
 mouth of the test tube. Now 
 heat the cupric oxide carefully 
 and keep it at a dull red heat 
 for five minutes. Let cool 
 slightly and, by means of a 
 towel, turn the tube until the 
 cupric oxide is uppermost. 
 Tap with a pencil until the 
 cupric oxide falls. Heat again 
 to redness for five minutes. 
 Remove the burner for five minutes ; then extinguish the flame 
 at the mouth of the tube ; let cool and weigh. Place the copper 
 in the receptacle provided. 
 
 Calculation. The loss in weight is oxygen. The weight of 
 the copper is obtained by subtracting the weight of the empty 
 tube from the weight after heating. 
 
 weight oxygen : weight copper : : 16 : atomic weight copper. 
 
 FIG. 23. 
 
112 LABORATORY STUDIES IN CHEMISTRY 
 
 EXERCISE 78 
 
 PERCENTAGE OF COPPER IN COPPER SULPHATE 
 CRYSTALS 
 
 ( Quantitative) 
 
 Apparatus. Same as in Exercise 77. 
 Material. Copper sulphate, CuSO 4 5 H 2 O. 
 
 Method. Copper sulphate, heated in illuminating gas, leaves a 
 residue of copper. 
 
 Use 1 gram of finely powdered copper sulphate and proceed 
 exactly as in Exercise 77. Clamp the tube near the mouth and 
 look out for the formation of water, which must be driven out 
 by the cautious use of the flame. Have the tube horizontal, or 
 the water will run back into the heated portion and produce 
 breakage. Heat strongly at the last. The calculation may be 
 left to the student. Compare your result with that calculated 
 from the formula according to the method of the textbook, 
 pages 89 and 385. 
 
 Place the copper in the receptacle provided. 
 
 EXERCISE 79 
 
 THE ATOMIC WEIGHT OF COPPER BY OXIDIZING 
 REDUCED COPPER 
 
 (Quantitative) 
 
 Apparatus. Porcelain crucible without cover. Triangle. Glass 
 rod. Balance. 
 
 Materials. Reduced copper from Exercises 77 and 78. 
 
 Method. Although ordinary copper cannot be completely changed 
 to oxide by heating, the reduced copper from Exercises 77 and 78 
 passes readily into cupric oxide at a red heat in the air. 
 
 Weigh the crucible and weigh in it from 0.5 gram to 1 gram 
 of copper, which must previously be finely powdered in a mortar. 
 Heat to redness for ten minutes. Let cool slightly and turn 
 over with a glass rod. Heat again to redness for ten minutes ; 
 cool and weigh. The calculation is similar to that of the atomic 
 weight of copper by reducing cupric oxide (Exercise 77). 
 
THE ATOMIC WEIGHT OF SULPHUR 113 
 
 EXERCISE 80 
 THE ATOMIC WEIGHT OF SULPHUR 
 
 (Quantitative) 
 
 Apparatus. Porcelain crucible and cover. Triangle. Balance. 
 Glass rod. 
 
 Materials. Cadmium oxide. Flowers of sulphur. 
 
 Method. Cadmium oxide when heated with sulphur passes into 
 cadmium sulphide : 
 
 CdO + 3S->CdS+ SO 2 . 
 
 From the increase in weight of the crucible, the atomic weight of 
 sulphur can be calculated. 
 
 Weigh accurately a crucible without cover and weigh in it 
 exactly 1 gram of cadmium oxide. Add a gram of sulphur 
 roughly weighed. Since the excess of sulphur will be driven 
 off by heat, the exact weighing of the sulphur would be useless. 
 Mix well with a glass rod and dust off the rod into the crucible. 
 Cover the crucible and place it on the triangle. 
 
 Turn the burner flame to full height and take the burner in 
 the hand. Heat carefully, keeping the flame in motion and 
 making sure that all parts of the crucible are heated, but not 
 to redness. Especially avoid letting the bottom glow. See that 
 the upper part, where the crucible and lid join, is thoroughly 
 heated. Blue flames of burning sulphur appear here between 
 lid and crucible. When they vanish, the heating is sufficient. 
 Do not heat too long. 
 
 Calculation. We start with the proportion : 
 
 weight CdO : weight CdS : : mol. weight CdO : mol. weight CdS, 
 
 mol. weight CdS = weight CdS x mol. weight CdO 
 
 weight CdO 
 
 Since the aotmic weight of cadmium is 112.5 and that of oxygen 
 16 we have : 
 
114 LABORATORY STUDIES IN CHEMISTRY 
 
 atomic Height S + 112.5 = weight CdS x 128.5 
 
 weight CdO 
 
 atomic weight S = weight CdS x 128.5 
 weight CdO 
 
 EXERCISE 81 
 THE FORMULA OF ZINC CHLORIDE 
 
 (Quantitative) 
 
 Apparatus. Conical flask (capacity 80 c.c.). Asbestos plate (wire 
 gauze can be used with care) . Small watch glass. Balance. 
 
 Material. Sheet zinc. 
 
 Method. Zinc dissolves in hydrochloric acid to form zinc chloride, 
 which can be obtained in anhydrous condition by evaporation. 
 
 Results are good only if the directions are exactly followed. 
 
 Weigh the flask, which must be dry, and place in it about 2 
 grams of zinc, accurately weighed. Add 10 c.c. concentrated 
 hydrochloric acid, cover with a watch glass and heat gently 
 witii a small flame (which does not touch the asbestos plate) 
 until the zinc is dissolved. Then increase the flame and 
 boil the liquid until the water is evaporated. This is indi- 
 cated by the fact that the formation of bubbles practically 
 stops. 
 
 Now reduce the flame until it does not quite touch the asbestos 
 plate and remove the watch glass. The zinc chloride will 
 solidify and then melt. Just as soon as it melts, stop heating 
 and weigh when cold enough to handle. Zinc chloride absorbs 
 water from the air, and if the flask is allowed to stand long 
 before weighing, it should be corked. 
 
 Calculation. 
 
 You have the weight of the zinc : the weight of the zinc 
 chloride is obtained by subtracting the weight of the flask 
 from the final weight. The chlorine is, of course, the differ- 
 ence between the zinc and the zinc chloride. 
 
OXYGEN IN POTASSIUM CHLORATE 115 
 
 Divide the weight of the zinc by the atomic weight of zinc, 
 and that of the chlorine by the atomic weight of chlorine. 
 You will obtain decimal fractions which will, however, be seen 
 to bear to each other approximately the relation of small 
 whole numbers. These are the numbers which must be added 
 to the symbols to give the formula. An example of the calcu- 
 lation is given in the textbook, page 385. 
 
 EXERCISE 82 
 
 PERCENTAGE OF OXYGEN IN POTASSIUM 
 CHLORATE 
 
 (Quantitative) 
 
 Apparatus. Pipestem triangle. Porclain crucible with cover. 
 Balance. Small test tubes. 
 
 Materials. Potassium chlorate. Potassium chloride. Silver 
 nitrate solution. Distilled water. 
 
 Method. The oxygen is driven off by heat and the loss in 
 weight obtained. 
 
 KC10 3 ->KC1 + 30. 
 
 Dissolve 0.2 c.c. potassium chlorate in 5 c.c. distilled water. 
 In another tube, dissolve 0.2 c.c. potassium chloride in 5 c.c. 
 distilled water. Add ten drops silver nitrate solution to each 
 tube. Results ? Potassium chlorate is apt to contain a trace 
 of potassium chloride, so that a slight precipitate may be ob- 
 tained in the first tube also. Weigh crucible, with cover, place 
 the cover on the balance pan beside the "crucible, and weigh in 
 the crucible 1 gram of potassium chlorate. Heat carefully for 
 ten minutes, keeping flame in motion ; apply the full heat of 
 the burner for five minutes more, cool and weigh without re- 
 moving cover. Calculate the percentage of oxygen, and com- 
 pare it with that calculated from the formula. 
 
 Examine the residue in the crucible. What is it ? Dissolve 
 it in water and add silver nitrate solution. Result ? 
 
116 LABORATORY STUDIES IN CHEMISTRY 
 
 ^ EXERCISE 83 
 
 THE EFFECT OF HEAT AND OF ACIDS ON 
 CARBONATES 
 
 Apparatus. Wire gauze. Hard glass test tube with one-hole 
 rubber stopper aud delivery tube bent at right angle. Evaporating 
 dish. Glass rod. Small test tubes. 
 
 Materials. Calcite (crystals or cleavage pieces). Magnesite. 
 Malachite (powder). Commercial copper carbonate can be used in- 
 stead of malachite. White lead. Lime. Red litmus paper. Lime- 
 water. 
 
 Method. Most carbonates are decomposed by heat, giving off car- 
 bon dioxide and leaving a residue of the oxide of the metal. Carbon 
 dioxide escapes when carbonates are dissolved in acids. 
 
 (a) Select two small pieces of calcite, not more than 1 cm. 
 (0.4 in.) long. Keep one for comparison. Support the other on 
 wire gauze and heat it with the full power of the burner for ten 
 minutes or more. Compare with the unheated piece. Look 
 especially at the edges for a change. If no distinct alteration 
 has occurred, continue heating until there is a visible result. 
 Write the equation for the chemical change which has taken 
 place. 
 
 Your equation, if correct, will call for the production of two 
 substances, one of which is lime. Verify this as follows : 
 Place a piece of red litmus paper in a clean dish and upon it 
 a fragment of good lime 2 mm. (0.08 in.) in diameter. Moisten 
 the lime with two drops of water, using a glass rod. Is there 
 any evidence of chemical change ? Write the equation. Now 
 add enough water to moisten both lime and paper and wait 
 several minutes. What does the change in the paper indicate ? 
 
 Clean the dish, place your unheated crystal on a fresh piece 
 of red litmus paper, and treat it in the same way. Is there 
 any change? 
 
 Now treat the crystal which has been heated in exactly the 
 same manner. Is your suspicion that lime is produced verified ? 
 
 The second substance called for by your equation for the 
 
EFFECT OF HEAT AND ACIDS ON CARBONATES 117 
 
 heating of calcite is a gas. The difficulty about verifying its 
 formation is that the temperature at which calcite decomposes 
 is so high that a glass tube would be melted. 
 
 (6) Magnesite differs from calcite in containing magnesium 
 instead of calcium. It behaves in the same way when heated 
 except that the temperature required is not nearly so high. 
 Select two pieces of it about 1 cm. in diameter. Reserve one for 
 comparison. Heat the other in the hard glass test tube. The 
 delivery tube dips into some clear limewater in a test tube. 
 The heat should be gentle at first and the final temperature 
 need not be high enough to soften the glass. Watch the 
 limewater intently during the whole progress of the experi- 
 ment. Take out the stopper before letting the hard glass tube 
 cool. 
 
 What gas escaped? Compare the magnesite which has 
 been heated with the unheated mineral as regards appearance 
 and cohesion. Compare the two in their behavior when 
 placed on red litmus paper and moistened. Wait patiently 
 for a result, as the action may be slow. 
 
 (c) Malachite is more complex because it is a basic carbon- 
 ate. This means that it contains copper hydroxide as well as 
 copper carbonate. Heat 1 c.c. of the powder in the same tube 
 used for the magnesite, first wiping the tube out thoroughly 
 with paper. The tube must be horizontal and the heat very 
 gentle. The delivery tube dips into a fresh portion of lime- 
 water. There are three products. What are they and what 
 is the evidence for their formation ? 
 
 The red litmus test would be useless in this case. 
 
 (d) Heat 1 c.c. of white lead in the same way as malachite. 
 Like malachite, white lead is a basic carbonate. Its formula 
 is Pb(OH), 2 PbC0 3 . What three products are formed ? 
 
 (e) Place a 2 mm. (0.08 in.) bit of calcite in a test tube, add 
 2 c.c. of water and 2 c.c. of concentrated hydrochloric acid. 
 Result ? What gas escapes ? Complete the equation : 
 
 CaCO q + x HC1 -> CaCL + H 9 O +.... 
 
118 LABORATORY STUDIES IN CHEMISTRY 
 
 Repeat, using nitric acid instead of hydrochloric. Complete 
 the equation : 
 
 CaC0 3 + x HN0 3 -> Ca(NO 3 ) 2 + H 2 O 4- -.. 
 
 In the same way, investigate the interaction of magnesite 
 and of malachite with hydrochloric and also with nitric acid. 
 Use a gentle heat, if necessary. Complete the equations : 
 
 MgC0 3 + x HC1 -> MgCl 2 + H 2 + ., 
 MgC0 3 + x HN0 8 -> Mg(N0 3 ) 2 + H a O + .... 
 
 In the case of malachite, the equations are more difficult and 
 are, therefore, given in full : 
 
 CuCO 3 Cu(OH) 2 + 4 HC1 -> 2 CuCl 2 + 3 H 2 O + CO 2 , 
 
 (Malachite) 
 
 CuCO 3 Cu(OH) 2 + 4 HNO 3 -> 2 Cu(NO 3 ) 2 + 3 H 2 O + CO 2 . 
 
 Make a general statement about the action of acids on car- 
 bonates. How could you ascertain whether a substance sub- 
 mitted to you was a carbonate or not ? 
 
 EXERCISE 84 
 
 THE EFFECT OF HEAT OK A CARBONATE ' 
 
 (Quantitative) 
 
 Apparatus. Porcelain crucible. Pipestem triangle. Small test 
 tubes. Balance. 
 
 Materials. Magnesium carbonate (powdered magnesite). 
 Method. See Exercise 83. 
 
 (a) Heat, in a test tube, a mixture of 2 c.c. hydrochloric 
 acid and 5 c.c. water nearly to boiling. Remove from the 
 flame and add 1 c.c. powdered magnesite. Result?- What 
 gas escapes ? 
 
 (b) Weigh a crucible without the cover and weigh in it a 
 gram of fine magnesite powder. Heat gently at first, finally 
 apply the full heat of the flame for fifteen minutes, cool and 
 weigh. If time permits, the exactness of the result is increased 
 
BORIC ACID AND BORAX 119 
 
 by reheating sharply for five minutes and weighing again to 
 see if the decomposition is complete. Use the lowest weight 
 obtained in your calculation. 
 
 The loss in weight is carbon dioxide : 
 
 MgCO 3 -> MgO + CO 2 . 
 
 What is the percentage of carbon dioxide yielded by mag- 
 nesite according to your results ? How does your result agree 
 with that calculated from the equation ? 
 
 (c) Test the substance in the crucible by throwing it into 
 a warm mixture of hydrochloric acid and water as in (a). 
 Result? 
 
 EXERCISE 86 l 
 BORIC ACID AND BORAX 
 
 Apparatus. Trip scales. Graduated cylinder. Beaker. Dish. 
 Small dry test tube. Glass rod. 
 
 Materials. Boracite. Boric acid. Borax. Sodium carbonate. 
 Alcohol. 
 
 Method. Boric acid is produced when borates are treated with 
 active acids. Borax is obtained when boric acid or a borate is treated 
 with a solution of sodium carbonate. 
 
 (a) Mix 10 grams powdered boracite with 10 c.c. concen- 
 trated hydrochloric acid and 10 c.c. water in a dish. Heat 
 gently for ten minutes. Filter hot and let cool. The crystals 
 are boric acid, H 3 B0 3 . Boracite is chiefly magnesium borate. 
 What, then, is the action of hydrochloric acid upon it ? What 
 magnesium compound must be contained in the liquid which 
 covers the crystals ? 
 
 (b) Dissolve 12 grams boric acid in 60 c.c. of boiling water 
 in a dish. Slowly add 10 grams anhydrous sodium carbonate. 
 Recalling the behavior of carbonates with acids, what gas 
 escapes ? What must exist in the liquid ? Evaporate until 
 
 1 If the period is short, it may be convenient to distribute (a), (6) 
 and (c) to different students. 
 
120 LABORATORY STUDIES IN CHEMISTRY 
 
 the liquid is half gone and let cool. Borax separates. Com- 
 pare the crystals with those of boric acid. Complete the 
 equation : 
 
 Na 2 C0 3 + x H 3 B0 3 -> Na 2 B 4 O 7 + y H 2 O + .... 
 
 (Boric acid) (Borax) 
 
 (c) Slowly add 10 c.c. concentrated sulphuric acid to 15 c.c. 
 water. Pour this liquid into a hot solution of 10 grams borax 
 in 50 c.c. water in a beaker. Let cool. Result ? Complete 
 the equation : 
 
 Na 2 B 4 O 7 + H 2 SO 4 + x H 2 O -> y H 3 BO 3 + Na 2 SO 4 . 
 
 (cT) If time permits, test borax for water of crystallization 
 by gently heating 2 c.c. from the stock bottle in a dry, clean 
 test tube clamped in a horizontal position. 
 
 (e) In a clean dish mix 1 c.c. of borax with 0.5 c.c. of con- 
 centrated sulphuric acid. Add 2 c.c. alcohol and set fire to 
 the liquid. Result ? This is a test for boric acid or a borate. 
 
 EXERCISE 86 
 
 THE ATOMIC WEIGHT OF MAGNESIUM 
 
 Apparatus. Wide-mouthed bottle holding about 400 c.c. Gradu- 
 ated 100 c.c. cylinder. Glass plate. Balance. Agate pan. 
 Material. Magnesium ribbon. 
 
 Method. Magnesium dissolves in hydrochloric acid : 
 Mg + 2 HCl-^MgCl 2 4- H 2 . 
 
 The atomic weight of magnesium can be calculated from the volume 
 of the hydrogen liberated. 
 
 Weigh accurately not more than 0.4 gram of magnesium 
 ribbon. The weight should be accurate to a milligram. If 
 your balance is not exact enough for this, weigh 2 m. of the 
 ribbon and calculate by proportion the length you must cut 
 off in order to get the weight you desire to take. If your 
 bottle holds less than 400 c.c., reduce the weight of magnesium 
 proportionally, taking not more than 0.1 gram for each 100 c.c. 
 
THE ATOMIC WEIGHT OF MAGNESIUM 121 
 
 capacity. Coil the ribbon into a spiral, smaller than the mouth 
 of the bottle. 
 
 Place 40 c.c. of concentrated hydrochloric acid in the bottle. 
 Fill the bottle with water, adding the water carefully so as to 
 allow the acid to remain at the bottom. With the aid of a 
 glass plate invert the bottle in an agate pan of water. The 
 water should be about 5 cm. deep in the pan. The bottle must 
 not contain air bubbles. If a. little air enters, withdraw the 
 bottle carefully, using the glass plate, set it upright upon the 
 desk, add water until it is completely filled, and try again. 
 
 Put the coil of magnesium ribbon in the pan, slide the 
 mouth of the bottle (under water) over it and set it down. 
 
 What gas collects ? What other substance must be formed 
 and dissolve in the water ? 
 
 When the action is over, add water to the pan or remove 
 water, as may be necessary to make the level of the water 
 inside and outside the same. Why ? Tightly cover the bottle 
 with the glass plate and remove it from the water, without 
 allowing any water to escape from the bottle. 
 
 Set the bottle upright on the desk, strike a match, take off 
 the glass plate, and instantly hold the burning match in the 
 mouth of the bottle. Result ? 
 
 With the graduated cylinder, measure (1) the water left in 
 the bottle, (2) the total capacity of the bottle. Subtract (1) 
 from (2) to obtain the volume of the hydrogen. 
 
 Calculation. Subtract one fourteenth from this volume for 
 expansion, due to the fact that the hydrogen is not measured at 
 standard temperature. Multiply the remainder by one fiftieth 
 and subtract to correct for the water vapor, which is measured 
 with the hydrogen, since it is collected over water. The re- 
 mainder will be approximately the volume which your hydro- 
 gen would occupy 4 at STP. 1 Since the weight of 1 c.c. of 
 hydrogen at STP is 0.00009 gram, the volume of your hydro- 
 gen in cubic centimeters multiplied by 0.00009 gives its weight 
 in grams. 
 
 1 STP means standard temperature and pressure, and 760 mm. 
 
122 LABORATORY STUDIES IN CHEMISTRY 
 
 The equation : 
 
 Mg + 2 HC1 -> MgCl 2 + H 2 
 
 shows that the atomic weight of magnesium in grams would 
 set free two atomic weights or 2.02 grams of hydrogen. Hence, 
 use the proportion : 
 
 Weight in grams of your hydrogen : 2.02 : : weight in grams of magne- 
 sium taken : atomic weight of magnesium. 
 
 Sample Calculation. 1 A student found that 0.4 gram of 
 magnesium produced 400 c.c. of hydrogen, measured under the 
 conditions of the experiment. Since -our measurements are 
 made with a cylinder which does not read to fractions of a 
 cubic centimeter, it is a waste of time to retain fractions of a 
 cubic centimeter in the calculation. 
 
 400 c.c. x YJ = 29 c.c. (correction for expansion). 
 400 c.c. - 29 = 371 c.c. 
 
 371 c.c. x sV = 7 c - c - (correction for water vapor) . 
 371 c.c. - 7 c.c. = 364 c.c. (volume at STP). 
 364 c.c. x 0.00009 = 0.03276 gram (weight of hydrogen). 
 0.03276:2.02 :: 0.4.x. 
 x = 24.66. 
 
 1 This calculation is approximate, but the error does not exceed the 
 probable error of the experimental measurement. The teacher may, 
 however, prefer to calculate the result by the more exact methods ex- 
 plained in Chapter 30 of the textbook. A third method is for the teacher 
 to calculate the weight of 1 c.c. of moist hydrogen, under the experimen- 
 tal conditions. This does not vary widely from 0.000082 gram. The 
 student then calculates the weight of the hydrogen by multiplication and 
 applies the proportion given above. 
 
THE PRODUCTION OF A DOUBLE SALT 123 
 
 EXERCISE 87 
 THE PRODUCTION OF A DOUBLE SALT 
 
 Apparatus. Two large test tubes. Three small test tubes. 
 Beaker. Glass rod. Trip scales. Graduated cylinder. Lens. 
 Funnel. 
 
 Materials. Copper sulphate (commercial). Ammonium sulphate 
 (commercial). Barium chloride solution. Lime. Filters. Iron 
 nails. 
 
 Method. When concentrated hot solutions of copper sulphate and 
 of ammonium sulphate are mixed and allowed to cool, copper ammo- 
 nium sulphate (CuSO 4 , (NH 4 ) 2 SO 4 , 6 H 2 O) is deposited in light blue 
 crystals. 
 
 Using decigrams 1 as your unit, weigh off the molecular weight 
 of copper sulphate (CuS0 4 5H 2 0). Hold a large test tube 
 nearly horizontal and place the copper sulphate in it. Add 
 30 c.c. water, clamp the tube at an angle of 45, and place under 
 it a small flame, just sufficient to heat the liquid to boiling. 
 
 Weigh off the molecular weight of ammonium sulphate 
 (NH 4 ) 2 S0 4 in decigrams, and treat it in the same way, using 
 only 20 c.c. of water. 
 
 When both salts are completely dissolved, mix the solutions 
 in a clean beaker and let cool. The double salt deposits. If 
 no deposit forms, the solution is supersaturated, and it may be 
 left as an exercise for the student to devise a method of caus- 
 ing crystallization to occur. Scrape the crystals on a filter, 
 using a glass rod. Examine the double salt with a lens and 
 compare it with copper sulphate and with ammonium sulphate. 
 Dissolve 2 c.c. of the double salt in 15 c.c. hot water and divide 
 the liquid into three portions in small test tubes. To one por- 
 tion add a few drops of barium chloride solution. Result ? 
 Is the double salt a sulphate ? To the second portion add an 
 
 1 Although both sulphates are cheap, the teacher may prefer to use 
 centigrams as a unit and one tenth the volume of water. Small test tubes 
 should then be used. 
 
124 LABORATORY STUDIES IN CHEMISTRY 
 
 iron nail arid let stand. Result? To the third portion add 
 2 c.c. of lime and heat gently. Note odor of the gas which 
 escapes. Test it with red litmus paper. Then hold in it a rod 
 wet with hydrochloric acid. Result ? What is proved by 
 these three tests ? 
 
APPARATUS AND SPECIAL MATERIALS 
 
 The following list includes the apparatus and chemicals 
 needed for the experiments in the Laboratory Studies. 
 
 Agate pan, round, 30 x 7.5 cm. (12 x 3 in.). 
 
 Asbestos boards, 10 cm. square. 
 
 Asbestos paper. 
 
 Balance beam balance sensitive to a milligram, if possible, with 
 weights from 50 g. to 1 mg. Such an instrument will cost about 
 ten dollars, slightly more if purchased with case provided with 
 sliding door and glass sides and back. Duty-free importation is 
 assumed. 
 
 Balance trip scales sensitive to a decigram with weights from 100 
 g. to 10 g. 
 
 Barometer. 
 
 Beakers, about 100 c.c. capacity. 
 
 Blowpipe, simplest form. 
 
 Bottles, common salt-mouth, about 400 c.c. capacity, no stopper. 
 
 Bottles, gas generating, 300 c.c. 
 
 Bunsen burner with wing-top. 
 
 Burette, Mohr form with rubber tube and pinchcock, 50 c.c., gradu- 
 ated to T ^ c.c. The Geissler burette with glass stopcock does not 
 work well in the hands of a beginner. 
 
 Cigar lighters (tobacconists' splints) for spark test. 
 
 Clamps (burette), one for each stand. 
 
 Cobalt glass, 10 cm. square. 
 
 Corks to fit large and small test tubes. 
 
 Crucibles, porcelain, with cover, capacity 25 c.c. 
 
 Deflagrating spoon, iron, small. 
 
 Dennison labels, Nos. 201, 213, 223. 
 
 Dishes, iron, capacity 70 to 100 c.c. 
 
 Dishes, lead, capacity 50 to 100 c.c. 
 
 Dishes, porcelain evaporating, capacity 125 c.c. 
 
 File, small triangular. 
 
 Filter paper. 
 
 125 
 
126 LABORATORY STUDIES IN CHEMISTRY 
 
 Filters, cut ordinary, 10 cm. 
 
 Flask, volumetric, 1 liter. 
 
 Flask, volumetric, 6 liters (optional, but very convenient). 
 
 Flasks, Erlenmeyer, 80 c.c. 
 
 Flasks, ordinary, 300 c.c. 
 
 Forceps, small steel, cheapest form. 
 
 Funnels, 75 mm. diameter. 
 
 Funnels, dropping, 80 c.c. capacity (optional, but convenient). A 
 
 fair substitute can be made by cutting a thistle tube and uniting 
 
 by a rubber tube bearing a clamp. 
 Glass plates 8 cm. square for covering bottles. 
 Glass rod, 3 mm. diameter. * 
 
 Glass tubing, 7 mm. outside diameter. 
 Glass tubing, 14 mm. outside diameter, hard glass. 
 Graduated cylinder, 100 c.c. graduated to 1 c.c. 
 Hammer with heavy iron plate for crushing minerals. 
 Kipp generator, simplest form (optional). 
 Lens, Coddiugton, 3 cm. focus. 
 Magnet, small horseshoe. 
 Medicine dropper. 
 Meter stick, centimeters and millimeters on one side, inches and 
 
 fractions on other. 
 Miner's safety lamp. 
 Mohr pinchcocks. 
 
 Mortar, 6 cm. porcelain, with pestle. 
 Platinum foil, 25 mm. square. 
 Platinum wire, B. & S. gauge, No. 25. 
 Pliers, gas, small. 
 
 Retort, 150 c.c. capacity, glass stopper. 
 Rubber bands (small). 
 Rubber stoppers, No. (1-hole) ; No. 2 (1-hole) ; No. 3 (solid, 1-hole, 
 
 2-hole) ; No. 5 (1-hole, 2-hole). 
 
 Rubber tubing for gas connections, cloth impression, 8 mm. bore. 
 Rubber tubing for apparatus connections, heavy wall, 4 mm. bore. (The 
 
 best grade of rubber stoppers and tubing should be purchased.) 
 Rubber tubing to renew clamps, cloth impression, 15 mm. bore. 
 Scissors, ordinary, for cutting paper, rubber tubing, etc. 
 Shears, tinner's, for cutting sheet metals. 
 
 Stand, about 150 cm. high, with one ring 7 cm. or 8 cm. in diameter. 
 Test tubes, 200 x 25 mm, 
 
APPARATUS AND SPECIAL MATERIALS 
 
 127 
 
 Test tubes, 150 x 18 mm. 
 
 Test tubes, 100 x 12 mm. (hard glass). 
 
 Thermometer, reading from - 10 C. to 150 C. 
 
 Thistle tubes (small). 
 
 Waste jar, 4 gallon, earthenware glazed. 
 
 Watch glasses, 5 cm. and 8.5 cm. 
 
 Wire cutter (electrician's, small). 
 
 Wire gauze, iron, 10 cm. square. 
 
 CHEMICALS, ETC. 
 
 Acid, Acetic. 
 Acid, Boric. 
 Acid, Formic. 
 Acid, Hydrochloric. 
 Acid, Nitric. 
 Acid, Oxalic. 
 Acid, Sulphuric. 
 Alcohol, 95 per cent grain. 
 Alcohol, Wood Spirit. 
 Aluminium (sheet or turnings). 
 Aluminium Sulphate. 
 Ammonia Water. 
 Ammonium Carbonate. 
 Ammonium Chloride (commer- 
 cial). 
 
 Ammonium Bichromate. 
 Ammonium Molybdate (solution). 
 Ammonium Nitrate. 
 Ammonium Sulphate. 
 Ammonium Sulphocyanide. 
 Aniline Red. 
 Arsenic, Metallic. 
 Arsenious Oxide. 
 Asbestos Fiber. 
 Barium Chloride. 
 Barium Nitrate. 
 Boneblack. 
 Borax. 
 Bromine. 
 
 Cadmium Oxide. 
 
 Calcium (metallic). 
 
 Calcium Carbide. 
 
 Calcium Carbonate (marble 
 
 cracked in 1 cm. fragments). 
 Calcium Carbonate (precipitated 
 
 chalk). 
 Calcium Chloride (commercial 
 
 dry). 
 
 Calcium Fluoride (powder). 
 Calcium Nitrate. 
 Calcium Oxide (lime). 
 Calcium Sulphate (powder). 
 Candles (Christmas-tree candles). 
 Carbon (charcoal ordinary). 
 Carbon (charcoal, prismatic for 
 
 blowpipe use). 
 Carbon (charcoal powder). 
 Carbon Bisulphide. 
 Cardboard. 
 Chloroform. 
 Chrome Alum. 
 Coal (bituminous). 
 Cobalt Chloride. 
 Cobalt Nitrate. 
 Cobalt Sulphate. 
 Cochineal. 
 Congo Red. 
 Copper Sheet (ordinary). 
 
128 LABORATORY STUDIES IN CHEMISTRY 
 
 Copper Sheet, 0.05 mm. thick. 
 Cotton Cloth (colored). 
 Cotton Cloth (muslin, white). 
 Cupric Carbonate (basic). . 
 Cupric Chloride. 
 Cupric Oxide. 
 
 Cupric Sulphate (commercial). 
 Cupric Sulphate (C. P.) 
 Cuprous Oxide. 
 Emery paper (fine). 
 Ether. 
 
 Ferrous Ammonium Sulphate. 
 Ferrous Sulphate. 
 Flannel (white). 
 Glucose. 
 Glue (solid). 
 Gold Leaf. 
 Hydrogen Peroxide. 
 Iodine. 
 
 Iron (powder by alcohol). 
 Iron Alum (ferric ammonium sul- 
 phate). 
 
 Iron Chloride (ferric). 
 Iron Filings. 
 Iron Nails. 
 
 Iron Sulphide (ferrous). 
 Kerosene. 
 
 Lead (granulated, test lead). 
 Lead Foil (tea lead). 
 Lead Nitrate. 
 Lead Oxide (litharge). 
 Lead, Red. 
 Lead, White. 
 Lithium Chloride. 
 Litmus Cubes. 
 
 Litmus Paper (red and blue). 
 Magnesium Oxide. 
 Magnesium Ribbon. 
 Magnesium Sulphate. 
 Malachite Green. 
 
 Manganese Dioxide (powder). 
 
 Mercuric Chloride. 
 
 Mercuric Oxide. 
 
 Mercurous Nitrate. 
 
 Mercury. 
 
 Molasses. 
 
 Nickel Nitrate. 
 
 Paraffin. 
 
 Paste (photographic, in tube). 
 
 Phenol -phthalein . 
 
 Phosphorus (red). 
 
 Picture Cord. 
 
 Pins. 
 
 Potassium Alum. 
 
 Potassium Bromide. 
 
 Potassium Carbonate (commer 
 cial). 
 
 Potassium Chlorate. 
 
 Potassium Chloride. 
 
 Potassium Chromate. 
 
 Potassium Cyanide. 
 
 Potassium Dichromate. 
 
 Potassium Hydroxide. 
 
 Potassium Iodide. 
 
 Potassium Nitrate. 
 
 Potassium Permanganate. 
 
 Potassium Sulphate. 
 
 Pyrogallol. 
 
 Rosin. 
 
 Sand. 
 
 Sandpaper. 
 
 Silver Nitrate. 
 
 Soda Lime. 
 
 Sodium. 
 
 Sodium Acetate (fused). 
 
 Sodium Ammonium Phosphate. 
 
 Sodium Carbonate (dry). 
 
 Sodium Carbonate Crystals (com- 
 mercial). 
 
 Sodium Chloride (C. P.), 
 
APPARATUS AND SPECIAL MATERIALS 
 
 129 
 
 Sodium Chloride (common salt). 
 
 Sodium Hydrogen Carbonate. 
 
 Sodium Hydrogen Phosphate. 
 
 Sodium Hydrogen Sulphate. 
 
 Sodium Hydroxide. 
 
 Sodium Nitrate. 
 
 Sodium Nitrite. 
 
 Sodium Potassium Tartrate (Ro- 
 chelle salt). 
 
 Sodium Sulphate. 
 
 Sodium Thiosulphate (commer- 
 cial). 
 
 Stannic Oxide. 
 
 Stannous Chloride. 
 
 Starch. 
 
 Strontium Chloride (optional). 
 
 Strontium Nitrate. 
 
 Sugar (ordinary). 
 
 Sulphur, Flowers. 
 
 Sulphur, Roll. 
 
 Superphosphate (fertilizer). 
 
 Tannic Acid. 
 
 Tartar Emetic. 
 
 Tin Chloride. 
 
 Tin Foil (pure, free from lead). 
 
 Thread. 
 
 Toluol. 
 
 Vaseline. 
 
 Water, Distilled. 
 
 Wire, Copper (No. 12 B. & S. 
 
 gauge). 
 Wire, Copper (No. 20 B. & S. 
 
 gauge). 
 Wire, Copper (No. 30 B. & S. 
 
 gauge). 
 Wire, German Silver (No. 36, B e 
 
 & S. gauge). 
 Wire, Iron, No. 20. 
 Zinc Dust. 
 Zinc, Mossy. 
 Zinc Oxide. 
 Zinc (sheet). 
 Zinc Sulphate. 
 
 MINERALS 
 
 Boracite. 
 
 Calcite (cleavage pieces). 
 
 Chalcopyrite. 
 
 Chrysocolla. 
 
 Cinnabar (10 per cent). 
 
 Galenite. 
 
 Gypsum. 
 
 Magnesite. 
 
 Orthoclase. 
 
 Phosphate Rock. 
 
 Pyrite. 
 
 Rhodonite. 
 
 Siderite. 
 
 Sphalerite. 
 
 (1) 
 
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 UNIVERSITY OF CALIFORNIA LIBRARY