IC-NRLF 355 A LABORATORY MANUAL IN CHEMISTRY THE MACMILLAN COMPANY NEW YORK BOSTON CHICAGO DALLAS SAN FRANCISCO MACMILLAN & CO., LIMITED LONDON ' BOMBAY CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, LTD. TORONTO A LABORATORY MANUAL IN CHEMISTRY BY WILLIAM CONGER MORGAN, PH.D. (YALE) ASSISTANT PROFESSOR AT THE UNIVERSITY OP CALIFORNIA AND JAMES A. LYMAN, Pn.D. (JOHNS HOPKINS) PROFESSOR OF CHEMISTRY, POMONA COLLEGE garfc THE MACMILLAN COMPANY 1916 All rights reserved COPYRIGHT, 1912, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published July, 1912. Reprinted October, 1912; February, September, 1913 ; March, 1914; January, June, September, October, 1915; February, August, 1916. Xortoooti J. 8. Cushing Co. Berwick & Smith Co. Norwood, Mass., U.S.A. PREFACE THIS manual is intended to accompany " Chemistry, an Elementary Textbook," by the same authors, but it may be used advantageously in connection with any other text. It will prove interesting to teachers who wish to present that kind of chemistry which appeals to students because of its intense human interest. The work outlined is intended for classes having eight to ten periods (approximately 45 minutes each), per week to devote to the subject. It is realized that this is more than can be given in all schools, so that a choice will some- times be necessary. Yet the better students need not be tied down to the amount of work required of the slower members. Where the allotted time is too short for each student to perform all the work, it will prove in- teresting if some students perform one experiment while others are doing another, both to be reported on in the classroom later. An abundance of material from which to choose is preferable to a minimum which must be amplified. The beginning student should be given an extended experimental introduction to the subject of chemistry, inasmuch as its methods of approach are unfamiliar to him and many of its facts beyond his personal experience. Hence, more time should be devoted to experimental work at the beginning of the course than later. Every teacher realizes that good lecture table experi- ments are quite as important as any feature of the course. There are included, therefore, a goodly number of experi- v 381717 vi PREFACE ments intended to be performed by the instructor while the class takes careful notes. These are generally too difficult for the average student, yet they cover points of such importance in the development of the science that students should see these demonstrations. The following experiments should be required of all students: 1, 2, 5, 10, 18, 19, 21, 22, 24, 26, 28, 29, 30, 34, 36, 39, 41 or 42, 44, 46, 49, 50, 51, 52, 53, 54, 57, 58, 59, 61, 64, 65, 67, 69, 72, 73. As many others should be per- formed as time will permit. Suggestions for the improvement of this manual from teachers who have used it with classes will be appreciated by the authors. W. C. MORGAN. BERKELEY, 1912. J. A. LYMAN. TABLE OF CONTENTS PAGE PREFACE v SUGGESTIONS TO TEACHERS x SUGGESTIONS TO STUDENTS * . xii PRELIMINARY EXERCISES BUNSEN BURNER 1 MANIPULATION OF GLASS TUBING ..... 2 EXPERIMENT 1. CHEMICAL AND PHYSICAL CHANGES 5 2. COMPOUNDS AND MIXTURES 6 3. WHICH REACT MORE READILY, GASES, LIQUIDS, OR SOLIDS ? 8 4. How CHEMICAL CHANGES ARE BROUGHT ABOUT . . 9 5. WHAT is FLAME ? 12 ^6. WHEN A SUBSTANCE BURNS, is THERE ANY CHANGE IN WEIGHT? 13 -7. Is THE TOTAL WEIGHT OF MATTER AFTER A CHANGE THE SAME AS THE TOTAL WEIGHT OF MATTER BEFORE THE CHANGE? 15 . THE GAS THAT MAKES A FIRE BURN 17 9. HOW MAY THE SPEED OF REACTIONS BE INCREASED? . 18 AQ. PREPARATION AND PROPERTIES OF OXYGEN . . . 19 -11. OXYGEN CONSUMED DURING COMBUSTION .... 21 12. HEAT EVOLVED DURING SLOW OXIDATION LEADS TO SPON- TANEOUS COMBUSTION 24 13. KINDLING TEMPERATURE 24 14. DIFFUSION 26 15. DECOMPOSITION OF WATER BY ELECTRICITY ... 28 16. DECOMPOSITION OF WATER BY METALS .... 31 17. ACTION OF METALS ON ACIDS .34 18. PREPARATION AND PROPERTIES OF HYDROGEN ... 35 -19. OXIDATION AND REDUCTION 38 20. NASCENT STATE 39 vii vm CONTENTS EXPERIMENT PAQB 21. DECANTATION, FILTRATION, AND DISTILLATION . . 40 22. How HEAT AFFECTS SOLUBILITY 43 23. SUPERSATURATION 44 24. SOLUTIONS OF GASES 45 25. CRYSTALLIZATION 46 26. WATER IN CRYSTALS 47 27. PURIFICATION BY CRYSTALLIZATION 50 28. REACTIONS RUN TO EQUILIBRIUM UNLESS PREVENTED BT SOME FACTOR 51 29. HYDROGEN CHLORID 55 30. CHLORIN 57 31. BLEACHING WITH HYPOCHLOROUS ACID .... 60 32. PERCENTAGE OF OXYGEN IN POTASSIUM CHLORATE . 62 33. DETERMINATION OF THE VOLUME RATIO IN WHICH HY- DROGEN AND OXYGEN COMBINE 65 34. BASES 66 35. NITROGEN ITS PREPARATION AND PROPERTIES . . 69 36. NITRIC ACID 71 37. NITROGEN MONOXID, OR NITROUS OXID .... 72 38. NITROGEN DIOXID, OR NITRIC OXID 74 39. AMMONIA 76 40. DECOMPOSITION OF AMMONIA BY ELECTRICITY ... 78 41. EQUIVALENT OF MAGNESIUM 79 42. EQUIVALENT OF SODIUM 80 43. PREPARATION OF AN ACID SALT 81 44. CARBON 82 J 45. MANUFACTURE OF ILLUMINATING GAS .... 84 46. CARBON DIOXID AND CARBONIC ACID .... 85 47. CARBON MONOXID 87 48. BURNING AND SUPPORTING COMBUSTION .... 89 49. FLAMES 90 50. HYDROCARBONS 92 51. ALCOHOL AND ACETIC ACID BY FERMENTATION . . 94 s. 52. SOAP 96 CONTENTS ix EXPERIMENT PAGE 53. CONSTITUENTS OF FOODS ....... 97 54. HALOGEN GROUP 101 55. BROMIN 102 56. IODIN 104 57. SULFUR 105 58. HYDROGEN SULFID 107 59. SULFUR DIOXID AND SULFUROUS ACID .... 109 60. SULFUR TRIOXID AND SULFURIC ACID . . . .111 61. PHOSPHORUS 112 62. PHOSPHIN . 114 63. ARSIN AND STIBIN 115 64. ELEMENTS THAT ACT BOTH AS ACID-FORMERS AND BASE- FORMERS 116 65. REDUCTION OF METALS FROM THEIR ORES . . . 117 66. BORIC ACID AND BORAX BEAD TESTS . . . .119 67. ALUM FROM CLAY 121 68. DYES AND MORDANTS 122 69. HARD WATER AND HOW TO SOFTEN IT .... 124 70. FLAME TESTS AND COLORED FIRE . . . . 126 71. MANUFACTURE OF POTASSIUM NITRATE .... 127 72. WASHING SODA, BAKING SODA, AND BAKING POWDERS . 128 73. REPLACEMENT OF ONE METAL BY ANOTHER . . . 130 74. REACTIONS OF SILVER SALTS IN PHOTOGRAPHY . . 131 75. EFFECT OF OXIDATION ON THE PROPERTIES OF ELEMENTS 132 76. BLUEPRINTS AND THEIR REACTIONS- 134 77. IDENTIFICATION OF SIMPLE SUBSTANCES .... 136 LISTS OF CHEMICALS AND SUPPLIES 139 MATERIALS TO BE OBTAINED LOCALLY AS NEEDED . . . 140 INDIVIDUAL APPARATUS 141 APPARATUS FOR GENERAL USE . 142 SUGGESTIONS TO TEACHERS IN the following experiments the shelf reagents are supposed to be about 10 per cent solutions ; say 100 g. of the solute in a liter of water. Concentrated reagents are of the specific gravities given below and the dilute reagents are made as specified. Hydrochloric acid, Sp. Gr. 1.19. Pour into 4 volumes of water. Nitric acid, Sp. Gr. 1.42. Pour into 5 volumes of water. Sulfuric acid, Sp. Gr. 1.84. Pour into 6 volumes of water. Ammonium hydroxid, Sp. Gr. 0.90. Pour into 4 volumes of water. A pneumatic trough may be made of a deep baking pan and a single muffin tin with two round holes cut in it by any tinsmith, as shown in Fig. A. Painted with asphalt varnish they will last for- ever. Fl <>. Capsules for sodium may be purchased, or made by cutting f-inch brass tubing (wall % inch) into 1-inch lengths and soldering a disk of brass air-tight on to one end. A 10-inch piece of copper wire, one end wrapped several times firmly about the capsule, serves as a holder. Rubber stoppers are much better than corks. Only best quality rubber goods should be purchased; the poorer grades oxidize quickly and become hard. Good rubber stoppers that have become hard may be softened by boiling in a 10 per cent NaOH solution. SUGGESTIONS TO TEACHERS xi To cut glass tubing of large diameter, make a short scratch with a file. Fold a filter paper so that its edges are parallel and moisten it. Wrap such a piece about the tube each side of the mark, leaving a space about of an inch wide exposed. Heat this space in a blowpipe with a fine flame, rotating the tube until it breaks; or touch the hot ring with a drop of water. To avoid repeated weighings on the part of students (see Exp. 22) make small measures out of glas? tubing of appropriate size sealed at one end. Weigh out 1 g. (if this is the desired amount) of the substance, insert in the tube, and jar it until the powder lies in the closed end. Cut off that part of the tube filled by the powder, affix to a wooden splint by means of glue and tough paper, and a serviceable measure has been made. Magnesium ribbon usually runs uniform and can be measured more accurately than weighed by students (see Exp. 41). The larger schools will find it very convenient to keep in the laboratory three Kipp generators, one fitted for hydrogen, one for hydrogen sulfid, and one for carbon dioxid. An oxone generator for oxygen is very handy. If a gas holder is not available, a satisfactory method of handling small volumes of gas is illustrated in Exps. 47 and 59. It is advisable to keep on hand in the laboratory a bottle containing olive oil and lime water (equal parts) to be used on burns. Shake thoroughly "before applying to the burn and bandage to keep from the air. A dilute solution of baking soda may be substituted for the lime water. SUGGESTIONS TO STUDENTS WHEN you enter the laboratory, learn the names of the apparatus and see that you have the complete list. If not, report it to the instructor. Wash your apparatus at the beginning and keep it scrupulously clean and your desk neat. Slovenly work causes experiments to go wrong, necessitating repetition. When work is completed for the day, put away the ap- paratus and clean the desk. Vessels of thin glass may be heated with safety. With thick glass, uneven heating causes irregular expansion and breaking. Always place a wire gauze between a beaker or flask and the flame. Test tubes and porcelain may be heated in the flame. Never heat glass containing a liquid at the surface of the liquid. It is sure to break. Heat as shown in Fig. B, using a strip of paper several times folded as a substi- tute for a test tube holder, if necessary. Shake the test tube continually while heating to prevent explosive boiling. Direct the mouth of the test tube away from yourself and your neighbor as well. Before attempting to insert glass into rubber, wet both. Don't push or pull, but twist a glass tube into position in a rubber stopper, thus avoiding cuts from broken glass. Before boring, soften a cork by rolling under the hand or foot. Select a borer one .size smaller than the tube to be fitted. Place the cork against a board and with a gentle pressure rotate it until it cuts neatly through. Do not attempt to push it through, as this makes ragged holes. xii SUGGESTIONS TO STUDENTS xin Be sparing in the use of reagents. Too much is often as detrimental to good work as too little. If too much of a liquid reagent has been removed, throw the excess away. Never pour it back into the bottle. The quanti- ties of reagents specified are usually only approximate and meant to be estimated rather than weighed or meas- ured. Learn to know how much 1 and 5 g. of ordinary substances are. An ordinary test tube (6 x f inches) holds 30 ccm. Learn what 5 and 10 ccm. are. Never lay the stopper of a reagent bottle down on the shelf or desk, thus contaminating it with other sub- stances. In obtaining reagents from bottles, turn the palm of the hand up and remove the stopper by grasping between the fingers and holding as FIG. C. shown in Fig . c. Never taste any reagent unless definitely told to do so, for most chemicals are poisons. In smelling, waft the fumes toward the nose with the hand. Dilute acids and solutions of reagents are always meant unless concentrated acids or solid reagents are specified. Always place the substance to be weighed on a piece of paper on the balance, never on the balance pan itself. To insert a powder neatly into a test tube, place it on one end of a narrow piece of paper folded lengthwise. Insert the paper into the test tube, turn upright and jar the powder from the paper. Throw only liquids in sinks; all paper and other solids in jars or boxes. After pouring acids into sinks, flush out with water. All temperatures are Centigrade; volumes and weights are in Metric Measures, familiarity with which is presup- posed on the part of all students. (Hood) means perform under a hood. LABOKATORY MANUAL IN CHEMISTKY PRELIMINARY EXERCISES THE BUNSEN BURNER Apparatus. Bunsen Burner and about 60 cm. of rubber tubing. Ring stand or tripod. Wire gauze. Beaker. NOTE. This burner was first made by the distinguished German scientist, Bunsen. Probably no other invention has done so much to facilitate work in the laboratory. Procedure, (a) The parts of the burner and their uses. Unscrew the tube of the burner, and notice the various parts. Then put the parts together again, using a little oil if the joints appear rusted, and connect the burner to the gas pipe by means of the rubber tubing. Having turned on the gas, light it by holding a burning match close to the burner tube about 1 cm. below the top. Turn the ring near the base of the burner until its openings coincide with the openings in the tube. This allows air to mix with the gas before the latter reaches the flame above. Turn the ring until the air is shut off. What changes are brought about in the flame by varying the supply of air ? Ascertain by means of a wire or glass rod which flame is hottest and which deposits soot. Which flame is most suitable for laboratory purposes? Hold the wire in different parts of the blue flame. Which is the hottest part of the flame ? While the flame is burning blue, hold a lighted match against one of the holes. The flame " strikes buck" and B 1 LABORATORY MANUAL IN CHEMISTRY burns at the base. Notice the odor, the character of this flame and the tem- perature of the burner tube. This flame is unsuitable for laboratory purposes. If a burner during use strikes back, the indication is that there is too much air mixed with the gas. To prevent the trouble, turn on more gas or shut off some of the air. If a burner strikes back, a sharp blow with the fist on the rubber tubing will usually restore the flame to its proper condition. If not, the gas must be shut off, after which it may be lighted again. (5) The use of wire gauze. Place the wire gauze on the tripod, and set the lighted Bunsen burner below the gauze. Notice how the gauze moderates the heat by distributing it over a larger sur- face, due to the fact that metals are good conductors of heat. A beaker of water may be boiled on the hottest part of the gauze without danger of breaking (see Fig. 1). FIG. 1. THE MANIPULATION OF GLASS TUBING Materials. Glass tubing, outside diameter about 5 mm. Rubber tubing, inside diameter a little less than the out- side diameter of the glass tubing. ^ ,. -^ \Y" t \ "liW Apparatus. A sharp, three-cornered file. A \. \ \7 Bunsen burner and wing top (Fig. 2) ; or a ^j common fishtail gas burner. FJG. 2. Procedure, (a) To cut glass tubing. Lay a piece of glass tubing on the table, and at the place where it is to be cut make a scratch with the file. Then grasp the tube firmly with a hand on either side of PRELIMINARY EXERCISES 3 the mark, and press with the tips of the thumbs opposite the scratch. The tube will usually break evenly across. (6) To smooth the end of a glass tube. Notice that the broken end of a glass tube is very sharp and would cut any soft object with which it comes in con- tact. Round off- the sharp edges by heating in a Bunsen flame, rotating the tube until the glass begins to melt slightly. Where it is not desirable to heat the tube, the sharp ends may be smoothed by sandpaper or by the flat side of a file. (c) To seal glass tubing. Heat a piece of glass tubing about 30 cm. long about 5 cm. from one end in the flame of the Bunsen burner, rotating it so that it may be evenly heated. When it becomes very soft, gently draw it out as shown in Fig. 3. Allow the tube to cool, then scratch with a file at the points A and J5, and break as previously directed. Hold the narrow end of the longer piece in the flame, rotating it until the edges melt together and the end is closed. Repeat the drawing out, cutting, and sealing on the other end of the tube and you have made a stirring rod. (cT) To lend glass tubing. Hold a piece of glass tubing lengthwise in the flattened flame of a fishtail burner or Bun- sen burner with wing top, as shown in Fig. 4, so that about 5 cm. of the tubing is heated where the bend is to be. Rotate the tube so that it may be evenly heated. When it is so hot that FIG. 4. it bends readily, remove it from 4 LABORATORY MANUAL IN CHEMISTRY the flame and immediately bend it into the desired shape, holding it in that position until the glass hardens. If the Bunsen burner has been used, turn off the supply of air, and by holding the tube in the yellow flame allow the bend to become covered with soot. This allows the tube to cool slowly, thus preventing unequal strains in the glass. This slow cooling, called " annealing," makes the glass less liable to break. If the bend is not smooth and even like Fig. 5 A, the tubing was not heated through a sufficient length, result- ing in flattening, B ; or else it was not heated uniformly, I N C H Eg. ABC FIG. 5. producing kinked and unsightly bends which usually break readily, O. Never attempt to make a bend by using the ordinary flame of the Bunsen burner. If a bend is needed near the end of a piece of tubing, make the bend in a longer piece that may be handled readily and afterwards cut off such portions as are unnecessary. Make exit and delivery tubes of the shapes and sizes indicated in A, D, and E, smoothing the ends in the flame, and preserve for future use. Three pieces like A will be needed in some experiments. EXPERIMENTS EXP. 1. CHEMICAL AND PHYSICAL CHANGES Materials. Colorless rock candy. Platinum wire. Magnesium ribbon or wire. Wooden splints. Apparatus. A mortar and pestle, small beaker and a test tube. A Bunsen burner, ring stand or tripod, and gauze. A test tube holder. Procedure. Examine a specimen of rock candy, notic- ing its properties, such as color, taste, hardness, and crys- talline form. Judging from its taste, of what does the rock candy consist ? 1. In a clean mortar pulverize 5-10 g. of rock candy. Note any change in properties. See whether the charac- teristic property, i.e. the taste of sugar, has been changed by the grinding. Is the substance still sugar ? 2. Partly fill the beaker with warm water and dissolve a little of the pulverized rock candy in it, stirring with a glass rod as the candy is added. What properties are changed? Taste the solution. Has the sugar been de- stroyed, or is it still in existence? 3. Heat some of the powdered rock candy in a dry test tube, applying the heat gently at first, noting carefully the progressive changes. When no further change takes place even at a more intense heat, remove the test tube and its contents from the flame. When the tube is cool, break it and examine the substance within. Taste it. Will it dissolve in water? Notice its color and softness. See whether it will burn. Does the sugar still exist? What does the new substance resemble? 6 6 LABORATORY MANUAL IN CHEMISTRY Compare the change brought about in 3 with the changes in 1 and 2, telling how they differ in their effect on the sugar. The change in 1 and 2 is physical. The change in 3 is chemical. 4. Heat successively in the flame of the burner pieces of wood, platinum wire, magnesium wire or ribbon, and glass. Compare the properties of the substances before heating with their properties after heating, and decide in each case whether the change is chemical or physical. Give reason for your answer in each case. EXP. 2. COMPOUNDS AND MIXTURES Materials. Powdered iron.* Sulfur. Carbon disulfid.t Apparatus. Test tubes. Magnifying glass. Magnet. Watch glass or evaporating dish. Procedure, (# ) The properties of sulfur. Note the visible properties of a piece of sulfur, exam- ining the powdered material with a magnifying glass. Touch it with a magnet. Burn a small bit of sulfur and cautiously notice the familiar odor. Drop a small piece of sulfur into 35 ccm. of carbon disulfid in a test tube and shake for about 5 minutes. (CAUTION : Do not bring carbon disulfid near a flame, as its vapor is very inflammable !) Does the sulfur seem to dissolve? Pour off the liquid from any undissolved sul- fur into a watch glass or evaporating dish and allow it to evaporate under a hood. If any sulfur is left upon the * Iron filings do not work as satisfactorily as powdered iron, which may be purchased from any chemical dealer. t Because of the way in which it is prepared (see text, p. 250) com- mercial carbon disulfid usually contains sulfur dissolved in it. For this experiment the carbon disulfid should be distilled to free it from sulfur and other impurities. EXPERIMENTS 7 watch glass, it must have been dissolved in the liquid. Did any of the sulfur dissolve in the carbon disulfid? This is a general method of testing whether a substance is soluble in a liquid. What are some of the characteristic properties of sulfur ? (5) The properties of iron. Examine some iron powder under a magnifying glass and touch it with a magnet. Ascertain whether iron powder will dissolve in carbon disulfid, proceeding as with sulfur. What are some of the characteristics of iron powder? (c) The characteristics of a mixture of iron and sulfur. Stir together 5 g. of powdered sulfur and 7 g. of iron powder. What is the color of the new powder. 1. Bring a magnet to some of the mixture. Does the iron still exist ? 2. Shake a pinch of the mixture in a test tube with 5 ccm. of carbon disulfid, carefully pour off the liquid from the undissolved material and evaporate on a watch glass. What is the residue left on the watch glass? Does the sulfur still exist in the mixture ? What is left in the test tube ? From the above tests, do the iron and the sulfur appear to retain their identity when they are mixed ? Is there any evidence indicating that any change has taken place ? (jd) The properties of a compound of iron and sulfur. Heat the rest of the mixture of iron and sulfur in a test tube with a small flame. When the mass begins to glow like a red-hot coal, remove it from the flame, as the change will continue without further heating. Lay the tube down on its side to cool. There is probably a little melted sulfur a part of the way up the inside of the 8 LABORATORY MANUAL IN CHEMISTRY test tube. Do not allow this to run down and mingle with the substance at the bottom. When the tube is cool, break it open and examine with a magnifying glass the substance left where the glow had been. Can the iron or the sulfur be seen ? Touch a flame to some of the substance. Does it burn ? See if any sulfur can be dissolved out of it by means of carbon disulfid. Bring a magnet to a lump of the substance. Can you detect either the iron or the sulfur in the new substance ? Through what kind of a change have the iron and the sulfur passed? The product is a chemical compound. How can you distinguish a mixture from a compound ? EXP. 3. WHICH REACT MORE READILY, GASES, LIQUIDS OR SOLIDS? Materials. Cone, ammonium hydroxid, hydrochloric acid and sulfuric acid. Alcohol. Potassium chlorate. Sulfur. Cream of tartar (hydrogen potassium tartrate). Baking soda (hydrogen sodium carbonate). Apparatus. Graduate. Mortar and pestle. Two small evaporating dishes or watch glasses. Test tube. Procedure, (a) G-ases. In a watch glass or evaporating dish put about 5 ccm. of cone, ammonium hydroxid solution and in another put the same quantity of cone, hydrochloric acid. Place the two liquids side by side so that the gases escaping from them may mix. If the liquids are warmed, the gases escape more readily. Catch some of the new substance on a piece of cold glass. What evidence do you observe that a chemical change is taking place ? (5) Liquids. Measure 10 ccm. of alcohol into a test tube, and to it add in small portions an equal volume of cone, sulfuric EXPERIMENTS 9 acid. A change of temperature usually accompanies a chemical change. Do you notice any? Is there any visible new product to show that a chemical change has taken place ? O) Solids. 1. Pulverize finely in jsej^ajrate * mortars 2 g. of potas- sium chlorate and 1 g. of sulfur. (CAUTION : Do not grind the two substances together !) Mix the powders thoroughly on a piece of paper, using the fingers only. Is there evidence of chemical action ? Save the powder for the next exercise. 2. Thoroughly mix together 4 g. of cream of tartar and 2 g. of baking soda, both finely powdered. Is there any evidence of a chemical reaction ? Save the mixture for the next exercise. State the relative readiness with which gases, liquids and solids react. EXP. 4. HOW CHEMICAL CHANGES ARE BROUGHT ABOUT Materials. The mixtures (potassium chlorate with sul- fur, and cream of tartar with baking soda) from the last exercise. Blue print paper. Copper sulfate solution. Sulfuric acid. Zinc dust. Powdered sulfur. Apparatus. A strip of zinc and of copper about 5 cm. wide and 10 cm. long. Two copper wires about 25 cm. long. Two platinum wires 5 cm. long. Beakers. Two dry cells. A compass. Procedure, (a) By mechanical means. Place the mixture of potassium chlorate and sulfur on a flat piece of iron or stone, and hit it a sharp blow with a hammer. What evidence is there of chemical action ? *Some students may pulverize the potassium chlorate, others the . 10 LABORATORY MANUAL IN CHEMISTRY Hit the head of a parlor match a light blow, and compare the results. Do you think these reactions are endothermic or exothermic ? (5) By light. Lay a piece of blue print paper, sensitive side up, on a book, put on the paper several coins, flat keys, or similar opaque objects, and expose the whole to bright sunlight until the parts of the paper on which the light shines have taken a bronzed appearance. Then remove the opaque objects from the paper, notice the appearance of the unexposed spots, and wash the paper in water. What evidence is there that a chemical change has taken place ? In making photographs does the picture get any darker after it is removed from the sunlight? Is the reaction endothermic or exothermic ? (js) By electricity.* " Make a hole near one end of the zinc and copper strips and connect the two by means of a copper wire. Place the metals in sulfuric acid, taking care that they do not touch each other. j- What happens? What evidence of a chemical reaction do you see ? The chemical energy liberated by the reaction is con- verted into electrical energy by this apparatus and an electric current is said to flow through the wire. Bring a compass near the wire and note the indication that a current is flowing, holding the compass first above, then below the wire. The current produced by this little cell is not suffi- ciently strong. For the following experiment substitute two dry cells arranged in series. * This part of the experiment may be performed by the instructor be- fore the class. t The metals may be kept from coming in contact by tying them with a piece of string on opposite sides of a strip of shingle or thin wood. EXPERIMENTS 11 Connect the copper wires to the poles of the battery. Without allowing the wires to come into contact with each other, touch them to the tongue and " taste the elec- tric current." Connect platinum wires to the ends of the copper wires. Dip the platinum wires into copper sulfate solution for 1-2 minutes. What evidence is seen that the passage of an electric current through the solution has caused a chemical change ? On which wire is the deposit ? What is it ? Is the reaction which has taken place analysis or synthesis ? Disconnect one of the copper wires from the battery. Then dip the platinum wires farther into the copper sul- fate solution, and ascertain if there is any chemical change when the circuit is broken and the supply of electrical energy is stopped. Is the reaction with the copper sulfate exothermic or endothermic ? (c?) By solution. Pour a little water on the mixture of cream of tartar and baking soda, so that the ingredients can dissolve. What evidence is there of chemical action ? Is the reac- tion exothermic or endothermic ? (e) By heat. Mix 7 g. of zinc dust with 4 g. of powdered sulfur. Is there any chemical action ? Place the mixture on a brick or piece of earthenware, and direct the flame of the Bunsen burner upon it until reaction begins. Then re- move the flame. What evidence is there of chemical action ? Is the reaction exothermic or endothermic ? What purpose was served by the heat that was first applied ? 12 LABORATORY MANUAL IN CHEMISTRY EXP. 5. WHAT IS FLAME ? Materials. Ether. Kerosene. Paraffin or tallow can- dle. Sawdust. Apparatus as shown in Fig. 6. Test tubes, burner, and ring stand. Procedure, (a) Recall that coal gas, illuminating gas and all other gases you know of burn with a flame (if they burn at all). (5) Put 3 ccm. of ether (CAUTION : Do not bring the bottle of ether near a flame!) in a test tube and smell of it. Can you detect it by its odor ? Is sufficient ether vaporizing to burn when the mouth of the test tube is brought to a flame ? Warm the test tube gently and see how it affects the size of the flame. Explain. () In a shallow crucible without a cover place 5-10 g. of metallic tin and weigh on a balance that is sensitive to 1 eg. Support the crucible in the triangle and heat, gently at first. After half an hour allow the crucible and contents to cool and weigh again. Is there a gain or loss of weight ? What does the change of weight indicate ? From what source must the new material have come ? NOTE. The metal has been heated in air exactly as the candle was. At high temperatures such metals burn with ( a flame. The products formed are the ashes of these metals, similar to the products of ordinary combustion. In the case of metals the ash weighs more than the original substance. Wood and coal leave some ash. Illu- minating gas, petroleum and a candle apparently burn to nothing and form no ash. Does combustion of a metal differ from combus- tion of a candle, or may it be that the ash of a candle is gaseous and so escapes notice? To test this point, perform the following ex- periment. () Slow combustion. 1. Of iron. Fill one of the tubes with water and invert it in a dish of water. Then fill the tube with oxygen. Close the end of the tube with the thumb and remove from the water. Carefully remove the thumb for a moment and introduce 5-10 g. of powdered iron. Cover with the thumb and shake the tube until the iron distributes itself over the inside of the tube. Then in- vert in a tall beaker of water and stand aside for a day or two. Explain what happens. Is there any significant difference between this reaction and that in the last experiment ? 2. Of phosphorus. Keeping the phosphorus under water, impale a piece about the size of a pea on the end of the wire. Place the other end of the wire in a beaker of water and slip over the phosphorus the closed tube, so arranging the quantity of water in the beaker that the phosphorus shall be out of water but inclosed in the tube full of air over water. Stand aside for three or four days until action ceases. Explain what happens. What is the difference between this experiment and that with the iron? This reaction offers a method for determining the pro- portion of oxygen in air. When the water ceases to rise inside the tube, showing that the reaction is complete, make the level of the water inside and outside the tube the same, either by raising the tube or by adding water to the beaker. Then ascertain the proportion of the gas absorbed. This is the proportion of oxygen in the atmos- phere. What do you find it to be ? 24 LABORATORY MANUAL IN CHEMISTRY EXP. 12. HEAT EVOLVED DURING SLOW OXIDATION LEADS TO SPONTANEOUS COMBUSTION Instructor's Experiment Materials. Yellow phosphorus. Carbon disulfid. Cotton. Procedure. Dry a small piece of phosphorus and lay it on a glass plate. . Notice how it smokes after a few seconds. How do you explain this action ? Dissolve a piece of dried phosphorus as large as a pea in about 5 com. of carbon disulfid in a test tube. By the aid of pincers or a piece of wire (CAUTION : Do not handle with the fingers !) dip a little cotton in the solu- tion of phosphorus and spread it out on the ring of an iron stand. The carbon disulfid evaporates quickly, leaving the phosphorus in finely divided condition, so that a large surface is exposed to the action of the air. Note what happens presently. How do you explain it? EXP. 13. KINDLING TEMPERATURE Materials. Yellow phosphorus. Sulfur. Paraffin. Sulfur matches. Parlor matches. Apparatus. A small pan, such as is used for a sand bath, or piece of sheet iron. Gauze. Tripod or ringstand. Procedure. (#) A study of a match. At equal distances from the center of the pan or piece of sheet iron and as far as possible from each other, place a small piece of dried phosphorus, of sulfur, of paraffin, and a match from which the head has been removed. Set the pan on a tripod, and under its center place a burner. Presumably the substances are heated equally rapidly. Notice the order in which the substances catch fire. That which takes fire first has the lowest kindling temperature. EXPERIMENTS 25 Examine a sulfur match. Do you get any indication of the substances composing it ? (Match heads formerly contained phosphorus, but because of its poisonous prop- erties, phosphorus sulfid is now used, its kindling temper- ature being about the same as for phosphorus.) Rub a similar match against a slightly roughened sur- face. What substance first catches fire? Whence does it derive the heat necessary to raise it to its kindling tem- perature? Which substance burns next? Whence does it derive the heat necessary to raise it to its kindling tem- perature? Which substance burns last? Repeat the work of the last two paragraphs, using parlor matches. What difference in the composition of parlor and sulfur matches is evidenced ? What would be the effect if a match were tipped with sulfur alone? (Try to ignite a piece of sulfur by friction.) If wood had a lower kindling temperature, which part of a match could be left out ? In burning iron in oxygen, why was the picture cord tipped with sulfur? (b) The kindling temperature of gases. Light a Bunsen burner, and bring down over the flame a piece of wire gauze. Why does the flame not burn above the gauze ? Is there unburned gas above the gauze ? To answer this question hold a lighted match above the gauze and explain the result. What cools the gas above the gauze below its kindling temperature ? Remove the gauze from the flame for a moment and, while it is still hot, bring it down into the flame again. Why does the gas above the gauze now catch fire ? Turn off the gas in the burner. Then turn it on again but do not light it, and bring down a piece of cold wire gauze to a distance of about 5 cm. above the top of the 26 LABORATORY MANUAL IN CHEMISTRY burner. Bring a lighted match above the gauze. Under proper conditions the gas burns above but not below the gauze. Why not? NOTE. The safety lamp, invented by Sir Humphry Davy and used by miners, depends on the principle illustrated in the preceding experiments. It consists of a small lamp surrounded by fine wire gauze. When brought into a mine where combustible gas is present, the gas passes readily through the wire gauze and burns brightly on the inside. The gauze conducts the heat of the flame away, and pre- vents the gas outside the gauze from becoming heated to its kindling temperature. Thus the miner is warned that a dangerous gas is present. EXP. 14. DIFFUSION Instructor's Experiment Materials. B-romin.* Cupric chlorid. Ammonia water (ammonium hydroxid). Alcohol. Alcoholic solution of phenolphthalein. Dilute sodium hydroxid solution. Apparatus. Fruit jar, or wide-mouth bottle, covered with glass plate. A thistle tube. Two cylinders cov- ered with glass plates or two large test tubes fitted with corks. A separating funnel or a pipette. Procedure, (a) G-ases. Through the thistle tube deposit about 1 ccm. of bromin inside on the bottom of a fruit jar. Remove the thistle tube and cover with a glass plate. Notice how, as the bromin vaporizes, it rises through the air until it soon fills the whole jar. Are the particles of which gases are composed capable of moving with great freedom ? * Avoid inhaling the fumes of bromin, as it attacks the nose and throat. The antidote is to inhale alcohol poured on a handkerchief. Do not allow liquid bromin to touch the skin, as it produces severe burns. If it does get on the skin, wash quickly with water and then with a dilute solution of baking soda. EXPERIMENTS 27 (5) Liquids. 1. Make a concentrated solution of cupric chlorid in a little cold water. To 1 com. of the solution in a test tube add a little ammonia water,, and notice the deep blue color produced when the liquids mix. By means of a thistle tube pour the cupric chlorid solution into a cylinder or large test tube until there is a layer 2-3 cm. thick, taking care not to spatter the sides of the cylinder. On the cupric chlorid solution float water. To float one liquid on another, cut a thin section from the top of a large cork, the thinner the better. Place the section of cork on the heavier liquid, and deliver the lighter liquid slowly upon the center of the cork, using a separating funnel or a pipette. When the test tube is about three fourths full, float a layer of ammonia water on the top of the others. Remove the section of cork and without disturbing the layers of / liquid, cover or cork the cylinder and set it where it canjf |M remain quiet for several days. It now contains cupric chlo- rid and ammonia separated by a considerable layer of water. From day to day notice the rise of the blue copper chlorid through the tube until it meets the ammonia diffusing down through the water, as is indicated by the deep blue color. 2. Try the effect of bringing together a few drops of an alcoholic solution of phenolphthalein and a little dilute sodium hydroxid solution. Then repeat the work outlined in the preceding paragraphs, placing in the bottom of the cylinder sodium hydroxid solution, on it floating a mixture of alcohol and water in equal pro- portions until the test tube is nearly full, and lastly 1 com. of an alcoholic solution of phenolphthalein. Remove the section of cork, close the test tube, and stand aside as in (1). Explain the final result. 28 LABORATORY MANUAL IN CHEMISTRY Are the particles of which liquids are composed capable of moving with considerable freedom ? How does this freedom compare with the freedom of motion of the particles of gaseous bodies ? (c) Diffusion takes place with solids just as with gases ^nd liquids, only much more slowly. In a previous exercise it was found that gases and liquids react chemically much more readily than solids. Suggest an explanation of this fact. EXP. 15. DECOMPOSITION OF WATER BY ELECTRICITY Instructor's Experiment Materials. Sugar. Cone, sulfuric acid. Sodium hy- droxid. Sodium sulfate. Apparatus as shown in Fig. 11, consisting of two graduated test tubes or measuring glasses. The bowl may be made by cutting a bottle. To do this, tie a string wet with kerosene tight about the bottle where it is desired to cut it. Set fire to the oil, rotating the bottle slowly as the oil burns. As soon as the string burns through, plunge the bottle in water. Fit the mouth of the bottle with a solid rubber stopper. Drive a wire nail through this stopper in two places, thus mak- ing holes through which the wires leading to the electrodes may pass. The electrodes consist of two pieces of platinum foil EXPERIMENTS 29 about 2 cm. long and 1 cm. wide, each welded * on to a platinum wire about 7 cm. long. If these wires are pushed through the holes in the stopper, it will close about them water-tight. Bend the platinum wires into the form of hooks and hang into them similarly hooked copper wires leading to the battery. When the bowl is filled with solution, the circuit is complete. Procedure. (&) Non-electrolytes. 1. Remove the measuring tubes and rinse, the whole apparatus with distilled water. Then pour distilled water into the bowl until it is nearly full. Connect the elec- trodes with a battery or some other source of electricity and attempt to pass a direct current through the water." Do you notice any indication that a current is passing? Is pure water an electrolyte or a non-electrolyte ? 2. Dissolve 5 g. qf sugar in the water in the bowl. Does the current now flow through the solution? Is sugar an electrolyte ? (6) Electrolytes. 1. Empty the sugar solution from the bowl, rinse with distilled water and refill, adding about 5 g. of sodium hydroxid to the water in the bowl and stirring to mix thoroughly. What difference do you notice ? Is sodium hydroxid an electrolyte or a non-electrolyte ? 2. Empty the contents of the bowl, rinse with distilled water and refill as before, adding sodium sulfate to the water. Describe what happens. Is sodium sulfate an electrolyte or a non-electrolyte ? * To weld platinum, lay the foil on a piece of flat iron, hold the wire in the position desired and heat both with a tine flame from a blowpipe. When they become red-hot, a light blow with a hammer will produce a firm weld. 30 LABORATORY MANUAL IN CHEMISTRY 3. Empty, rinse and refill the bowl as before, adding to the water about 10 ccm. of cone, sulfuric acid, stirring well as before. Is the acid an electrolyte ? (c) Electrolysis of water. Disconnect the wires and stop the current. Fill the graduated test tubes or measuring glasses with solution from the bowl, close with the thumb, and invert in the bowl, placing one test tube over each electrode. See to it that no bubbles of air have gained access to these meas- uring tubes. Start the current again, so regulating its strength as to cause a steady liberation of bubbles without any undue heating of the wires or the solution. Note the rate at which the gases are liberated. When a sufficient amount of the gases has been collected, break the circuit, and measure the amount of gas in each tube to the nearest cubic centimeter, first adjusting the tubes so that the water level is right. If this cannot be satisfactorily accomplished in the bowl, close the tubes with the thumb and remove to a vessel of water of suffi- cient depth. No correction for pressure, temperature or moisture is necessary, as the gases are under the same conditions when measured. What is the relation between the volumes of the two gases ? Slip the thumb over the mouth of the tube containing the smaller amount of gas, remove it from the water, turn it mouth up, and test its contents with a glowing spark. What gas does it contain ? The gas in the second tube is called hydrogen. In a similar way remove the second tube from the solution, and test its contents with a lighted match or other flame. What happens ? In each of the above instances the current will continue to flow through the solution until the water is used up EXPERIMENTS 31 and the other substance is left. Furthermore, by evapo- rating any of the three solutions mentioned the original substance, sodium hydroxid, sodium sulfate or sulfuric acid may be recovered. This shows that the catalytic agents are not used up but that the gases come from the decomposition of the water. What can be said, then, as to the composition of water? (c?) Calculations of results. 1. Multiply the volume of oxygen by 0.00143 g., the weight of 1 com. of oxygen. Multiply the volume of hy- drogen by 0.00009 g., the weight of 1 com. of hydrogen. Divide the weight of the oxygen by the weight of the hydrogen. How many parts by weight of oxygen are present in water for every 1 part of hydrogen ? How many parts by weight of water contain 1 part by weight of hydrogen ? 2. Add the weights of oxygen and hydrogen. The sum is the weight -of the water decomposed. The weight of 1 ccm. of steam is 0.0008 g. Calculate the volume which this water would have occupied if, instead of being decomposed, it had been converted into steam. 3. Fill in the blanks in the following statements : .By weight, 1 part of hydrogen unites with ( ) parts of oxygen to give ( ) parts of water. By volume ( ) parts of hydrogen unite with 1 part of oxygen to give ( ) parts of steam. EXP. 16. DECOMPOSITION OF WATER BY METALS Instructor's Experiment Materials. Iron filings, tacks or nails. Sodium. Potassium. Apparatus as shown in Fig. 12, consisting of a flask for 32 LABORATORY MANUAL IN CHEMISTRY generating steam connected with a piece of iron pipe about 50 cm. long and 2-3 cm. in diameter, containing iron filings or nails. From this pipe an exit tube leads into a bottle, as shown in the figure, in which the excess steam condenses. From this a delivery tube dips under the surface of a pneumatic trough. If a furnace is not available, heat the tube with several Bunsen burners. A FIG. 12. metallic capsule for sodium and a stiff wire for a holder (see Suggestions to Teachers)* Wide-mouth bottle. Procedure, (#) Decomposition of water by iron. First performed by Lavoisier in 1783 with a gun barrel, furnish- ing the first proof that water is not an element. Heat the middle of the iron pipe to redness and pass in steam from the flask. After the air has been driven from the apparatus, collect some of the gas in an inverted bottle filled with water. When the bottle is full cover with a glass plate and remove the bottle from the water. Keeping the bottle inverted bring to a flame and remove cover. Describe what happens. Is the gas apparently like either gas formed when water is decomposed by means of electricity ? EXPERIMENTS 33 The gas is hydrogen, its odor being due to impurities. Iron is an element. Where must the hydrogen come from? Fill a bottle half full of hydrogen, raise from the water, thus allowing air to enter and mix with the hydrogen. Bring to a flame and note result. Bring out clearly the effect of mixing air with hydrogen. Iron and some other metals decompose water at high temperature ; magnesium at boiling temperature ; others at ordinary temperature. (5) By sodium or potassium. 1. Throw a piece of sodium about the size of a small pea on a dish of water, holding a sheet of glass between you and the dish to prevent spattering. What happens ? 2. Throw a similar piece of potassium into water. What happens? The action with potassium is similar to that of sodium except for the flame. Either the metal burns or else a gas is given off which burns. 3. To settle this point, fill a capsule with sodium, twist it firmly into the wire holder. Fill a bottle with water, cover with a glass plate and invert in a pan of water, being sure that no air gets into the bottle. Lean the bottle against one edge of the pan and quickly thrust the capsule, mouth down, under the mouth of the bottle (see Fig. 29). Regulate the flow of gas by slightly in- clining the capsule as the action slackens. If careless handling allows the sodium to escape from the capsule, stand back until all action ceases. Describe what happens. When action is complete, cover the mouth of the bot- tle with a glass plate, remove from water and stand bottle upright. Bring a flame to the mouth of the bottle and remove the glass cover. What happens ? 34 LABORATORY MANUAL IN CHEMISTRY The gas is hydrogen, colored yellow by sodium. Sodium and potassium are elements. Where does the hydrogen come from ? Dip the ringers in the water into which the sodium and potassium were thrown and note the effect. This is due to compounds of these metals dissolved in the water (see Exp. 34). EXP. 17. THE ACTION OF METALS ON ACIDS Materials. Small pieces of zinc, magnesium, copper, kV^ibm and of iron, such as coarse filings or small nails. Sulfuric, hydrochloric and acetic acids. Apparatus. Test tubes and an evaporating dish. Procedure, (a) Fill a test tube one quarter full of sul- furic acid, then fill to the top with water. Close the tube with the thumb and invert in an evaporating dish con- taining water. Roll about 7 cm. of magnesium ribbon into a ball, slip it under the mouth of the test tube and note action. When the tube is full of gas, close with the thumb and bring to a flame. What happens ? The gas is hydrogen. Magnesium is an element. Where must the hydrogen have come from ? (See if magnesium acts on water to liberate a gas.) (5) Without attempting to collect the gas as in (a) see if there is any action between the following metals and acids by adding to 5 ccm. of acid in a test tube a piece of the metal. Warm the acid if necessary to get action but do not heat to boiling. State whether the action is slow, medium or rapid in the following cases : Zinc and sulfuric acid. Zinc and hydrochloric acid. Zinc and acetic acid. Iron and sulfuric acid. EXPERIMENTS 35 Tin and hydrochloric acid. Magnesium and acetic acid. Copper and sulfuric acid. Copper and hydrochloric acid. Many metals (not all) decompose many acids (not all) with the liberation of hydrogen. (Set up the apparatus for the next experiment so that it will be ready at the beginning of the period.) EXP. 18. PREPARATION AND PROPERTIES OF HYDROGEN Materials. Sulfuric acid. Granulated zinc or small pieces of sheet zinc. Solutions of potassium permanga- nate and copper sulfate. Wooden splints. Cobalt chlorid test paper (see Exp. 26). Apparatus as shown in Fig. 13 consisting of a bottle whose capacity is about 300 ccm. The thistle tube reaches almost to the bottom of the bottle. A piece of clay pipestem. Two 250 ccm. flasks closed with corks. A test tube. 4-6 fruit jars or wide-mouth bottles. Procedure, (#) Preparation. Put 20-25 g. of granulated FlG< 13 ' zinc into the bottle, insert the stopper (fitted with the thistle tube and delivery tube as shown) tightly, and through the thistle tube pour in enough sulfuric acid to cover the end of the thistle tube. If the action is slow, add a little copper sulfate solution and shake the bottle. What is the effect ? The copper sulfate is decomposed by the zinc, the copper being de- posited on the zinc as is shown by the dark coloration. The copper then acts as a catalytic agent. 36 LABORATORY MANUAL IN CHEMISTRY CAUTION : The hydrogen liberated is at first mixed with air. A hydrogen and air mixture is explosive ; hence keep all flames away from the apparatus at this stage of the work. To ascertain when the hydrogen is sufficiently pure, collect a test tube of the gas over water, cover with the thumb and, keeping the test tube inverted remove it to a flame. If a whistling noise is heard, the hydrogen is still mixed with air. When it burns with only a quiet puff at the beginning, it is sufficiently pure. Collect six bottles of hydrogen gas, after sealing allow- ing them to stand inverted until used. If the flow of gas slackens, introduce through the thistle tube additional acid. Keep the apparatus for the next experiment. (5) Properties. 1. Place one jar of hydrogen mouth upward on the table and another mouth downward. Remove the seal from second jar and hold it mouth downward above the table. Then remove the cover from the upright jar. After about a minute bring both jars to a flame. Do you detect hydrogen in both bottles ? If not, from which one has it escaped ? How did it escape from this bottle ? What does this indicate as to the relative weights of hydrogen and air ? 2. Note whether hydrogen has any color, taste or odor. If impurities give to the gas an odor, they may be re- moved by treating with a dilute solution of potassium permanganate acidified with sulfuric acid. Slide the cover glass partly from a jar of hydrogen and quickly (Why use haste ?) introduce the permanganate solution. Shake the covered jar for a few minutes and then test odor again. 3. Remove the seal from a jar of hydrogen and, hold- EXPERIMENTS 37 ing it mouth downward, thrust well into the jar a lighted splinter of wood and hold it there until all action ceases (see Fig. 14). What do you observe ? Does hydrogen support combustion as well as burn ? 4. Slip into the end of the rubber tube attached to the outlet tube of the generator a piece of clay pipestem and light the escaping hydrogen. Hold in the flame a wire or piece of glass tubing. Does the flame seem to be very hot? Hold a clean, well-corked flask filled with cold water 20-30 cm. above the hydrogen flame. What happens ? Blow out the hydrogen flame and hold the second clean, well-corked flask filled with cold water in the hydrogen as it escapes unburned. What happens ? A test for water is given on page 48. Rub off the de- posit on the first flask with a piece of cobalt chlorid paper, made blue by warming. What happens ? What was the deposit on the first flask ? Explain its formation. ( Lead oxid + hydrogen -> Consult the text, page 61, and see how -this experiment might be made of use in determining quantitatively the composition of water. EXP. 20. THE NASCENT STATE Materials. 200 ccm. of distilled water, to which is added just enough potassium permanganate to impart a decided color. Cone, sulfuric acid. Apparatus. Four beakers. A hydrogen generator. Procedure. Divide the water containing potassium per- manganate solution into four portions. 1. To one portion add 5 ccm. of cone, sulfuric acid. 2. Into another portion drop a few grams of zinc. 3. Into a third portion drop a similar amount of zinc, and then add 5 ccm. of cone, sulphuric acid. 4. Through the last portion allow hydrogen from the generator to bubble. After about 20 minutes compare the results in the four solutions. In which case is there a chemical change re- sulting in the bleaching of the potassium permanganate ? Can sulfuric acid alone cause the bleaching ? Can zinc alone ? What do they produce when they react ? Does ordinary hydrogen cause the bleaching? In what condi- tion is hydrogen most active ? 40 LABORATORY MANUAL IN CHEMISTRY EXP. 21. DECANTATION, FILTRATION AND DISTILLATION Materials. Filter papers. Sand. Salt. A light in- soluble powder, such as precipitated chalk (calcium car- bonate) or magnesia (magnesium oxid). Red ink or potassium permanganate solution. Apparatus. Funnel, ring stand, beakers and stirring rods. Distillation apparatus as shown in Fig. 18, consist- ing of a condenser, boiling flask of about a half liter capacity fitted to it and a receiving flask of about half this capacity. If a condenser is not available, a long piece of glass tubing, a meter or more in length, will serve the purpose if the boiling is sufficiently slow to allow the air to cool and condense the steam. Procedure, (a) Decantation. Stir a little sand into a beaker half full of water, then allow the mixture to stand for a few minutes. To what extent does the sand settle out of the water ? See how completely you can separate the sand by carefully pouring off the water. This process of pouring off is called de- cantation; the sand is typical of any heavy insoluble substance. Mix about 50 g. of sand with 10 g. of salt, add 50 ccm. of water, stir well, then allow to settle and see how com- pletely you can decant into a beaker the liquid without allowing any sand to be poured off. Taste and measure the liquid. Where is the salt ? Calculate how much of the salt was removed from the sand by decanting the liquid. Add 50 ccm. of water to the beaker containing the sand, stir, settle and decant as before. Calculate how much salt is left with the sand after the second decantation. Continue the process until the taste of salt is no longer perceptible. How many decantations were necessary to EXPERIMENTS 41 separate the salt and sand ? What class of substances can be separated from what other class of substances by this method ? Suggest practical uses of the process of de- cantation. (by Filtration. To 50 ccm. of water add about 5 g. of salt and some precipitated chalk or magnesia, stir well and allow to settle for a few moments. Do you judge that decantation would be as suc- cessful now as in (#) ? Why ? Fold a filter paper as shown in Fig. 16 and open it into a cone having three thicknesses of paper on one side and one on the other. Fit it into a funnel, moisten with a little water and press the paper snugly against the sides of the funnel. Sup- port the funnel in a ring stand, placing a beaker beneath it. Stir up the mixture previ- ously prepared and pour it gradually upon the filter paper in the funnel, always keeping the liquid well below the top of the paper. To avoid spattering and prevent drops running down the sides of the beaker, hold the middle of a glass rod against the edge of the beaker and pour the liquid along the rod on to the side, not the tip, of the filter FIQ. 17. , paper, as shown in Fig. 17. FIG. 16. 42 LABORATORY MANUAL IN CHEMISTRY This process is called filtration. The liquid which runs through it is called the filtrate : the substance remaining in the filter is the residue. Ascertain by tasting whether the salt is in the residue or the filtrate. Can dissolved substances be separated from liquids by filtration ? What substances can be separated by filtration ? Suggest prac- tical uses of the process of filtration. () Substances not separable by crystallization. Dissolve 3.5 g. of potassium sulfate and 13 g. of alumi- num sulfate in about 40 com. of hot water, and set the solution away to cool. When crystals have formed, re- move them and by their taste identify them. Are these crystals a new substance or are they the same as one of the ingredients in the mixture ? EXP. 28. REACTIONS RUN TO EQUILIBRIUM UNLESS PREVENTED BY SOME FACTOR Materials. Cone, nitric (HNO 3 ), sulfuric (H 2 SO 4 ), and hydrochloric (HC1) acids. Potassium nitrate, KNO 3 . Potassium hydrogen sulfate, KHSO 4 . Potassium chro- mate, K 2 CrO 4 . Sodium carbonate, Na 2 CO 3 . Lead nitrate, Pb(NO 3 ) 2 . Pieces of copper. Apparatus. Beakers. Test tubes. Stirring rods. 52 LABORATORY MANUAL IN CHEMISTRY Procedure, (a) Reactions running to equilibrium, not to completion. 1. Test and see that solutions of potassium nitrate, potassium hydrogen sulfate and sulfuric acid do not attack copper but that nitric acid does. 2. To 10 ccm. of water in a beaker add cautiously 10 ccm. of cone. H 2 SO 4 and mix thoroughly. Make a saturated solution by heating 20 g. of potassium nitrate with 10 ccm. of water and divide into two equal portions. To half of the potassium nitrate solution add 5 ccm. of the H 2 SO 4 (1:1) solution. Pour a few drops of the mixture upon copper and note the action, warming if necessary. What causes this action? Stand the remain- der aside to cool and crystallize. Note the formation of clear needles of potassium nitrate. 3. Heat the other half of the potassium nitrate solution (prepared above) if necessary to keep the KNO 3 in solu- tion and add 10 ccm. of the H 2 SO 4 (1:1) solution. Pour a few drops of the mixture upon copper and note the action. What causes this action ? Stand the re- mainder aside to cool and crystallize (if necessary over- night). Note the formation of opaque crystals of potas- sium hydrogen sulfate. Discussion. Between potassium nitrate and sulfuric acid the only reaction which can take place under the condition of these experiments is represented by the equation : potassium hydrogen hydrogen potassium hy- nitrate + sulfate < > nitrate -f- drogen sulfate KNO 8 + H 2 SO 4 -> HNO t + KHSO 4 That some HNO 8 is formed in (2) is indicated by the fact that the mixture attacks copper; for, of the four sub- stances represented in the equation, HNO 3 is the only EXPERIMENTS 53 reagent which will attack copper. This proves that some KNO 3 has reacted with H 2 SO 4 to form HNO 3 . Yet, on cooling, potassium nitrate separates from the solution, proving that all of the KNO 3 has not reacted with the H 2 SO 4 present. In other words, the reaction does not run to completion but to equilibrium, all four of the sub- stances being present in solution. In (3) twice the proportion of sulfuric acid is added that was present in (2). The mass action of the H 2 SO 4 on the KNOg causes the reaction to run much further toward completion than in (2), as is indicated by the crys- tallization of KHSO 4 instead of KNO 3 from the solution. All four substances are still present in the mixture but there is more KHSO 4 than KNO 3 . When none of the substances present in a reacting mixture are removed from the sphere of action, reactions run to equilibrium. Nitric acid boils at 120.5, H 2 SO 4 at 330; KNO 3 and KHSO 4 are volatile only at higher temperatures. By heating up the mixtures in (2) and (3) water will boil away first. When the temperature rises above 121, HNO 3 will become a gas and boil away. What effect will this have on the reaction ? Why ? Before answer- ing this question perform (5) if necessary. (&) Reaction running to completion. 1. Equilibrium prevented by the formation of a gaseous substance. To 10 ccm. of water add a drop or two of HC1. Taste the solution and note one of the characteristic properties of acids. Dissolve 15 g. of sodium carbonate crystals (or 8 g. of anhydrous Na 2 CO 3 ) in 25 ccm. of boiling water. Dilute 10 ccm. of cone, HCl with an equal volume of water and 54 LABORATORY MANUAL IN CHEMISTRY heat to boiling. Remove from the flame and add gradu ally the sodium carbonate solution until a further slight addition of the latter produces no effervescence. Then cool the liquid and taste it. Is HC1 any longer present ? What common substance seems to have taken its place ? Do you judge that any gaseous substance was formed during the reaction ? Why ? The equation representing the reaction which has taken place is f sodium hydrogen sodium water carbon carbonate + chlorid > chlorid 4- + dioxid Na 2 C0 3 + 2 HC1 -> 2 NaCl + H 2 O + CO 2 Which of the reaction products escaped as a gas? Ex- plain in detail how the formation of a gaseous substance causes the reaction to run to completion. 2. Equilibrium prevented by the formation of an in- soluble substance. Dissolve about 1 g. of potassium chromate in 100 ccm. of water and 2 g. of lead nitrate in about 20 ccm. of water and heat both solutions to boiling. Add half of the lead nitrate solution to the potassium chromate solution, stir thoroughly and allow the mixture to stand for a few minutes. When the precipitate has settled, add to the clear liquid above it a few drops of the lead nitrate solu- tion. If a precipitate forms, add 1-2 ccm. more, stir and allow to settle once more. Test the clear liquid as before and add the lead nitrate solution, a little at a time, as long as a precipitate forms. Then filter the solution. If the filtrate is colored, add more lead nitrate and filter again. All chromates are intensely colored. Judging from the color of the filtrate, does it contain any chromate ? Judging by the color, where is the chromate ? Did the reaction run to equilibrium or to completion ? By evapo- EXPERIMENTS 55 rating the filtrate, needle-like crystals of potassium nitrate could be obtained. Where did the potassium come from ? Where the nitrate ? The equation representing the change is : potassium lead lead potassium chromate + nitrate > chromate -f- nitrate K 2 CrO 4 Pb(NO 3 ) 2 -> PbCrO 4 + 2 KNO 3 EXP. 29. HYDROGEN CHLORID, HC1 Materials. Salt, NaCl. Cone, sulfuric acid, H 2 SO 4 . Magnesium ribbon. Manganese dioxid, MnO 2 . Copper oxid, CuO. Nitric acid, HNO 3 . Silver nitrate (AgNO 3 ) solution. Ammonia water (ammonium hydroxid), NH 4 OH. Litmus paper. Apparatus. A 250 com. flask fitted with thistle and exit tubes as shown in Fig. 19. A bottle. Piece of card- board with hole in center. Procedure, (#) Prepara- tion. To 10 ccm. of water in a beaker add cautiously 15 ccm. of cone. H 2 SO 4 and allow the mixture to cool. Set up the apparatus as shown in Fig. 19. Place about 25 g. of salt in the flask, insert the stopper, and through the thistle tube pour in the H 2 SO 4 solution previ- ously prepared. Hydrogen chlorid is evolved at once but the flask may be warmed if necessary to hasten action. Complete the equation : H 2 SO 4 4- 2 NaCl -> FIG. 19. 56 LABORATORY MANUAL IN CHEMISTRY (5) Properties. Is the gas colorless and invisible while (1) inside the flask ; (2) outside the flask or bottle as it escapes into the air ? Blow gently across the top of the bottle from which the gas is escaping. What causes the change in the appear- ance of the gas? In answering this question recall what happens to a cold window pane when breathed upon. Note the odor of the gas. Hold a moistened finger for an instant in the bottle of gas, and then touch the finger to the tongue. Bring a lighted match into the gas. Does it burn or support combustion ? Withdraw the delivery tube from the bottle and insert it as far as possible in a test tube and collect some gas by downward displacement. Close the test tube with the thumb and invert in a dish of water. Remove thumb and explain the result. Why not collect the gas over water ? (e) Hydrochloric acid, HC1. Put about 20 ccm. of water into the bottle and again introduce the delivery tube, keeping the end just above the surface of the water. Continue the action as long as gas is readily absorbed. Prove the identity of the solution of hydrogen chlorid thus obtained with the hydrochloric acid of the laboratory bottle by making the first four of the following tests on each liquid. 1. Note the effect of each on blue and red litmus paper. 2o Dilute considerably and note the taste. 3. Put 10 ccm. in a small test-tube and fill with dis- tilled water. Invert in a dish of water and test the action of magnesium on each liquid, as directed in Exp. 17, (V). Are the reactions the same in each case ? What is one constituent of hydrochloric acid ? EXPERIMENTS 57 4. Heat 10 com. in a test tube with a little man- ganese dioxid. Are the reactions the same in each case ? The other constituent of hydrochloric acid, thus liberated, is chlorin. 5. Shake about 1 g. of copper oxide with 10 ccm. of hot water. Is it soluble ? Add 5 ccm. of HC1 and heat if necessary. Is there any reaction ? How do you know? The substance formed is copper chlorid, CuCl 2 . Write an equation showing its formation. 6. To a dilute solution of hydrogen chlorid or other chlorid, add a little nitric acid and a few drops of silver nitrate solution. Note the character of the precipitate which appears. To one portion of the liquid containing the precipitate add ammonia water until the solution will turn red litmus paper blue. What happens to the pre- cipitate ? Other soluble chlorids besides hydrogen chlorid give these same reactions. This procedure is used as a test for chlorids. The taste of hydrochloric acid, its action on litmus paper and on many metals and oxids are properties pos- sessed by acids in general. State these general properties of acids. EXP. 30. CHLORIN Materials. Cone, hydrochloric acid, HC1. Manganese dioxid, MnO 2 . Yellow phosphorus. Thin copper foil. Charcoal. Turpentine. A candle twisted into a wire for a holder. Potassium hydroxid (KOH) solution. Apparatus as shown in Fig. 20. 3-4 bottles having the same size neck interchangeable with A. Wooden block. Beaker. A hydrogen generator with a clay pipe- stem tip. 58 LABORATORY MANUAL IN CHEMISTRY Combustion spoon. Filter paper. Pieces of cardboard or glass plates. NOTE. Chlorin is a very irritating gas, the effects of which may be counteracted by inhaling .the fumes of alcohol sprinkled on a hand- kerchief. This whole experiment should be performed under a hood or in a good draft. Procedure, (a) Preparation. Place about 30 g. of manga- nese dioxid in the flask and set up the apparatus as shown in Fig. 20. Through the thistle tube introduce about 50 ccm. of cone. HC1. Chlorin will be evolved at once but the flask may be warmed when neces- sary to hasten the reaction. To prevent chlorin from get- ting into the room, cover the end of the exit tube in the beaker with water. When this becomes yellowish, show- ing that it is nearly saturated, add potassium hydroxid solution until the color disappears. Keep the resulting liquid for the next exercise. Fill 6-8 bottles with the gas by downward displacement, removing A as soon as it takes on a yellowish color and substituting one of the other bottles. Cover each bottle, when removed, with a cardboard or glass plate. As soon as you have collected one or two bottles of gas, begin to perform the experiments, refilling these bottles for the later experiments. Complete the equation : MnO 2 -f 4 HCl-> Is MnO 2 an oxidizing or reducing agent ? What other substances that you have worked with do you think might be substituted for MnO in this reaction ? FIG. 20. EXPERIMENTS 59 (5) Physical properties. Note the color and odor of chlorin. Compare with the color and odor of the water in the beaker in which the exit tube dips. Is chlorin soluble in water ? ( HC1 + HOC1 What industrial use for chlorin and hypochlorous acid do you know of ? EXP. 32. THE PERCENTAGE OF OXYGEN IN POTASSIUM CHLORATE THE WEIGHT OF ONE LITER OF OXYGEN Materials. Potassium chlorate, KC1O 3 , dried on a radiator or in an oven. Apparatus as shown in Fig. 21. A is a test tube of hard glass, connected by a one-holed rubber stopper and a delivery tube to the liter bottle B. It is fitted with a tight rubber stopper pierced with two holes. Through one hole passes the tube lead- ing from A. Through the other hole passes a tube, D, shaped like an inverted U, one arm of which reaches to the bottom of B. C is a 500 ccm. beaker. Barometer arid thermometer for general class use. Procedure. Set up the apparatus as shown and see that all joints are tight by sucking on the end of the FIG. 21. EXPERIMENTS 63 U-shaped tube ; then remove the test tube and weigh it carefully on a delicate balance. Into the tube put 1-1.5 g. of potassium chlorate. Jar the tube so that the potas- sium chlorate collects at the closed end, and then weigh again. Weigh the 500 ccm. beaker to a tenth of a gram on a platform scale. Fill the bottle nearly full of water and cause the tube D to fill with water by blowing gently into the delivery tube leading from A and plug the end of the U-tube with a squill of filter paper. Insert the stopper and delivery tube tightly into the test tube con- taining the potassium chlorate. Remove plug from U- tube and place weighed beaker under the open end. Heat the tube A in the flame of the burner until no further change in its contents takes place. Move the burner back and forth at first so as to make a gentle heat, but afterwards make it intense enough to decompose all of the potassium chlorate. If the molten mass froths and leaves a deposit high up in the tube, heat this deposit until it melts and runs back to the bottom. When all the oxygen has been driven off and only molten potassium chlorid remains in the tube A, allow it to cool. Raise or lower the beaker so that the inverted U-tube dips as far into the water in the beaker as it does into the water in the bottle. Then remove the beaker and the test tube in the order named and weigh the test tube again on the delicate balance. Take the tempera- ture of the water as that of the gas and note the barometric pressure. Tabulate results thus . Weight of tube and potassium chlorate Weight of tube empty (a) Weight of potassium chlorate taken .... Weight of tube and potassium chlorate Weight of tube and potassium chlorid ( 6) Weight of oxygen lost t 64 LABORATORY MANUAL IN CHEMISTRY () Neutralization. Place 20 ccm. of NaOH solution in a beaker, add a few drops of phenolphthalein, and add, with stirring, HC1 until the color just disappears. To be sure that no excess of acid is present, add NaOH drop by drop until the pink color reappears, then finally bleach with a single drop of acid. Dip the fingers into the resulting solution, taste and smell it. Can you detect either base or acid ? To be sure that the solution is not merely a mixture in which the properties of the acid hide those of the base, and vice versa^ evaporate the solution to dry ness and taste the solid left. What is it? Has a new substance been formed? To what class of substances does it belong? Write an equation expressing its formation. ( 2 NaOH + H 2 O 2 Fill the other half of the bottle containing nitrogen dioxid with oxygen. What happens? The brown gas is nitro gen tetroxid, N 2 O 4 . What constituent of the air is it that causes nitrogen dioxid to turn brown ? 3. Insert a burning splint into a jar of gas, removing the cover only as little as is necessary. Does nitrogen , dioxid burn or support combustion ? Place a piece of phosphorus in a combus- tion spoon, ignite and insert in a bottle of nitrogen dioxid. What happens ? Nitrogen dioxid is decomposed into its elements at the temperature produced by burning phosphorus, but not at the temperature of a burning splint. Explain the pre- ceding results on this basis. (c) The reactions. Several different reactions take place at the same time when nitric acid acts on copper. The metal is oxidized by nitric acid to the oxid which then dissolves in more acid to form a salt as the equations show. 2 HNO 3 -> H 2 O + N 2 O 2 + O 3Cu + ---- > - 3 + HNO 3 -> 3 Cu(NO 3 ) 2 + - What colors the liquid in the generator blue ? 76 LABORATORY MANUAL IN CHEMISTRY EXP. 39. AMMONIA, NH 3 Materials. Ammonium chlorid, NH 4 C1. Freshly slaked lime (calcium hydroxid) Ca(OH) 2 . Cone. HC1. Litmus paper. Wooden splint. Apparatus. As shown in Fig. 27. Three bottles. Procedure, (#) Preparation. Take a quarter of a test tube full of ammonium chlorid and the same amount of calcium hydroxid. Smell of each and note whether either has an odor. Mix the two sub- stances thoroughly on a paper and cautiously smell again. What is the odor ? How could it have been produced ? What would be the effect of raising the temperature? Complete the equation Ca(OH) 2 + 2 NH 4 C1 -> CaCl 2 + + Put the mixture into the test tube and set up the ap- paratus as shown in Fig. 27 and heat gently. Turn the outlet tube up and collect a bottle full of gas by upward displacement as shown by the dotted lines. What does this indicate as to the relative density of air and ammonia? (#) Properties. 1. Hold a moistened finger in the gas and touch to the tongue. What is the taste of ammonia ? 2. Thrust a lighted wooden splint up into the bottle of ammonia. Does it burn or support combustion ? 3. Put 3-4 drops of cone. HC1 in a bottle, cover with a glass and shake thoroughly. Lift the bottle containing FIG. 27. EXPERIMENTS 77 NH g from over the outlet tube of the generator, cover with a glass plate and then place mouth upward on the table. Place the bottle containing the HC1 mouth down- ward over the bottle containing the N H 3 and remove both glass plates. Note what happens. Stand the bottles aside in order that the substance may settle. After it has settled remove the upper bottle and allow any am- monia to escape. 4. Collect some ammonia in a test tube by upward dis- placement, cover with the thumb and invert in a pan of water. Remove thumb and explain results. Why not collect ammonia over water ? (c) Ammonium hydroxid, NH 4 OH. Turn the outlet tube of the generator down and insert it in a bottle containing about 20 com. of water, keeping the end of the tube just above the surface of the water as shown in Fig. 27. Why not dip it into the water? Shake the bottle occasionally to mix the liquid thoroughly and continue the reaction as long as the gas is readily absorbed by the water. Satisfy yourself that the liquid in the bottle is identical with the ammonium hydroxid of the laboratory by noting the odor and effect on red litmus paper of each solution. A reaction must have taken place between the gas and the water. Complete the equation _ + _ -- 1. Heat in a test tube about 10 ccm. of the solution in the bottle, noting by the odor what comes off first. Continue the heating until about half of the liquid is boiled away. Can you now detect any ammonia? What must have happened to the ammonium hydroxid ? Is the reaction written above reversible or not ? 2. Add dilute HC1 to the remainder of the liquid in 78 LABORATORY MANUAL IN CHEMISTRY the bottle until it will just turn blue litmus paper red. Evaporate to dryness and compare the product obtained with that formed in (5) 3, as to taste, odor, effect of heat, and of sodium hydroxid upon each. The substance is in each case ammonium chlorid, NH 4 C1. Write equations expressing its formation in each case. 3. Any ammonium salt heated with a strong base, such as NaOH, KOH or Ca(OH) 2 , will liberate ammonia, which may be detected by the odor or by red litmus paper. This is a test for ammonium salts. EXP. 40. DECOMPOSITION OF AMMONIA BY ELECTRICITY Instructor's Experiment Materials. Cone, ammonia water (ammonium hy- droxid), NH 4 OH. Salt. Wooden splints. Apparatus. Same as used in the decomposition of water by electricity, Fig. 11. Procedure. Into the bowl of the apparatus place a suf- ficient quantity of a mixture of cone, ammonium hydroxid and water (equal volumes) to cover the electrodes and dissolve in the mixture about 25 g. of salt. Fill the graduated test tubes or measuring glasses with the solu- tion and invert over the electrodes. Connect the wires to a dynamo or battery and note the evolution of gas. At what rate does it collect in each test tube ? When one of the tubes is full of gas remove it from the bowl and holding it mouth down thrust up into it a lighted wooden splint. What gas does it contain ? When the other tube is full of gas, test it similarly. What happens? This gas is nitrogen. How many volumes of hydrogen combine with one vol- ume of nitrogen to form ammonia ? NOTE. The reaction which takes place is not as simple as it ap- pears. Investigation shows that it is the salt which is decomposed EXPERIMENTS 79 by the electric current, sodium being liberated at the cathode and chlorin at the anode. Consult Exp. 16 (7;) and explain why hydrogen is collected at the cathode in this experiment. Recalling the action of chlorin on compounds containing hydrogen (see Exp. 30 (c)), ex- plain why nitrogen collects at the anode. What other product is formed by the sodium ; by the chlorin ? What becomes of these two products when they come together in the solution? What then is the action of the salt in the present experiment? Write equations for all the reactions involved. EXP. 41. THE EQUIVALENT OF MAGNESIUM Materials. Cone. HC1. Magnesium ribbon. Apparatus. As shown in Fig. 28 consisting of a half liter flask, small evaporating dish and pan of water. Stiff card or small square of glass. Gradu- ate, thermometer, and barometer for general class use. Procedure. Weigh accurately not more than 0.5 g. of magnesium ribbon.* Roll or tie it into a little ball that will readily slip into the neck of the flask. Place the ball of magnesium in the dish and the dish in the pan containing suf- ficient water to cover the dish to a depth of 3 to 4 cm. Put 25 ccm. of cone. HC1 into the flask and fill with dis- tilled water. Cover the mouth of the flask with a card or small square of glass and invert in the pan of water outside the dish. Quickly bring the inverted flask over the magnesium in the dish so as to catch all the hydrogen liberated but allowing no air to enter the flask. When the metal is completely dissolved, cover the mouth of the flask with the glass plate and remove to sink or deep vessel previously filled with water and adjust the flask so as to make the level of water the same inside * See Suggestions to Teachers. 80 LABORATORY MANUAL IN CHEMISTRY and outside the flask. Cover the mouth of the flask with the glass plate, remove from the bowl and place upright on the table. By pouring from a graduate, ascertain the volume of water necessary to fill the flask even full. The volume of water added equals the volume of hydrogen liberated. Note the temperature of the water (equal to the tem- perature of the gas) and read the barometer. Subtract the pressure due to water vapor (see text, p. 410) from the barometric reading to get the real pressure of the hydrogen. Reduce the volume of hydrogen to standard conditions and calculate the weight of magnesium neces- sary to liberate 1 g. of hydrogen. This result is the equivalent of magnesium as obtained in your experiment. Repeat with another piece of magnesium, if time permits, and average the results. Record your results as follows : EXP. 1 EXP. 2 Weight of magnesium taken . . g. g. Volume of hydrogen obtained . ccra. ccm. Temperature Barometer ........ mm. mm. Water vapor pressure .... mm. mm. Pressure of hydrogen .... mm. mm. Volume hydrogen (standard con- ditions) ccm. ccm. Equivalent of magnesium . . . Average EXP. 42. THE EQUIVALENT OF SODIUM Apparatus. Wide mouth bottle of 250-500 ccm. capa- city, pan of water, capsule (for holding sodium) and wire for holder as shown in Fig. 29. Wire nail to fit the cap- sule. Stiff card or small square of glass. Graduate, thermometer and barometer for general class use. EXPERIMENTS 81 Procedure. See that the capsule is thoroughly clean and dry and weigh it accurately. Cut off any crust from some pieces of sodium and remove any oil with filter paper. Fill the capsule even full with clean sodium, using the head of the nail to press it tightly into the capsule, and weigh. Twist the wire firmly about the capsule, being sure that it cannot drop out. Fill the bot- tle with water and invert in the pan of water, taking care that no air enters. Lean the bottle against the side of the pan as shown in Fig. 29, and quickly thrust the cap- sule, mouth downward, under the mouth of the bottle so as to catch all the gas liberated. When the flow of gas slackens, tilt the capsule slowly so that water may again come in con- tact with the sodium, and finally turn the capsule mouth upward. If care- less handling causes the sodium to escape from the cap- sule, stand back until all action ceases. When the action is complete, measure the hydrogen evolved and take the temperature and pressure. Calcu- late and record the results as directed in Exp. 41. Repeat if time permits and average the results. EXP. 43. PREPARATION OF AN ACID SALT Materials. Cone. H 2 SO 4 . Solid KOH. Phenolphtha- lein solution. Litmus paper. Zinc. Apparatus. Beakers. Evaporating dish. Stirring rod. Graduate or 20 ccm. pipette. Procedure. Dissolve 7 g. of solid KOH in 20 ccm. of water. Add 10 ccm. of cone. H 2 SO 4 to 40 ccm. of water. Measure 20 ccm. of the H 2 SO 4 solution into an evaporating dish, add 15 ccm. of the KOH solution, and cool. To the 82 LABORATORY MANUAL IN CHEMISTRY mixture add a drop of phenolphthalein solution and, stir- ring constantly, neutralize with the remaining KOH solu- tion added drop by drop, until a faint pink color is produced. Write an equation indicating what has been formed. What kind of a salt is it ? What other methods of forming salts do you know? To the neutralized solution now add 20 com. of the H 2 SO 4 solution and evaporate until a little of the sub- stance removed on a glass rod solidifies on cooling; then remove from the flame and cool. Note the properties of the hydrogen potassium sulfate thus formed. Dissolve a bit of it in water and cautiously taste the solution and note its action on blue litmus paper. Put some of the salt in a test tube with a piece of zinc, add a little water and notice the result. Is hydrogen potas- sium sulphate an acid as well as a salt? Write an equation indicating its formation. EXP. 44. CARBON Materials. Coal, wood, paper, bread, potato, vegetables, starch, cotton, wool, meat, candle. Sand. Kerosene. Powdered wood charcoal. Animal charcoal. Hydrogen sulfid water. Dark brown sugar. Copper oxid, CuO. Lime water, Ca(OH) 2 . Apparatus. Clay crucible or iron dish. Ring stand or tripod. Beakers. Test tube with cork. Funnel. A hard glass test tube fitted with stopper and exit tube as explained in (PbS + EXP. 46. CARBON DIOXID, C0 2 , AND CARBONIC ACID, H 2 C0 3 Materials. Marble or limestone, CaCO 3 . Cone. HC1. Lime water, Ca(OH) 2 . Wooden splint. Bread. Candle. Apparatus such as was used in making hydrogen, Fig. 13. Test tubes. Beaker. Wire. Litmus paper. Procedure, (a) Preparation. Put 10-20 g. of marble or limestone into the generat- ing bottle, add 50 ccm. of water, insert the stopper and through the thistle tube pour 5 ccm. of cone. HC1. Col- lect three bottles of gas, adding more acid from time to time if necessary to hasten the action. Complete the equation : CaCO 3 + HC1 -> + H 2 CO 3 -> + CO 2 Any of the common acids may take the place of HC1 in this reaction. Why ? (5) Physical properties. Note the color, odor, and taste of carbon dioxid and ascertain whether it will burn or support combustion. 86 LABORATORY MANUAL IN CHEMISTRY Set a lighted candle in a bottle of air and invert over it a bottle of carbon dioxid. Explain the result. ( Ca(OH) 2 + H 2 CO 3 -> + CaC0 3 + H 2 C0 3 -> CaH 2 (CO 3 ) 2 (c?) Testing for carbon dioxid. When treated with HC1, any carbonate liberates carbon dioxid just as marble does. The formation of a precipitate in lime water is a test for carbon dioxid and carbonates. Carbon dioxid is so heavy that it may be poured from one bottle to another just like water, as the following experi- ment shows. 1. Pour about 20 ccm. of lime water into a bottle and shake it. No significant change should occur, though, on long standing, lime water shows the presence of small amounts of carbon dioxid in the air. (Try it.) Pour a bottle of carbon dioxid into the lime water and shake again. What happens ? 2. Hold a burning wooden splint in a bottle of air EXPERIMENTS 87 until it is extinguished, add a little lime water and shake. What is the result ? Where did the carbon dioxid come from ? 3. Stick a piece of bread on a wire, hold it in a flame until it takes fire, then lower it into another bottle of air. When the flame goes out, test with lime water as before and explain where the carbon dioxid comes from. 4. Blow the breath through a glass tube into a little lime water. Explain the result. How was the carbon dioxid in the breath produced ? What similarity is there in the burning of coal or wood under the boilers of an engine and the use of food in the body ? Why is the tem- perature produced higher in one case than the other ? What causes the body temperature to be higher than that of the atmosphere ? EXP. 47. CARBON MONOXID Instructor's Experiment Materials. Charcoal. Oxygen. NaOH. Lime water. Apparatus as shown in Fig. 12, except that the iron pipe is replaced by a combustion tube of hard glass. This is supported in the furnace on a strip of sheet iron to prevent sagging of the tube when heated. In place of the boiling flask a 2-liter bottle is attached to the com- bustion tube by means of an exit tube, passing through a 2-hole rubber stopper fitting the neck of the bottle. Through the other hole in the stopper passes an inlet tube reaching to the bottom of the bottle, the outer end being connected to the water tap. Short piece of rubber tubing. Pinch cock. Procedure. Fill the 2-liter bottle with oxygen by dis- placement of water and insert the stopper carrying the inlet and exit tubes. Close the inlet tube with a piece of 88 LABORATORY MANUAL IN CHEMISTRY rubber tubing and a pinch cock. Fill the combustion tube with small pieces of wood charcoal * (no dust) and connect it to the oxygen bottle. Pour NaOH solution into the wash bottle until the end of the inlet tube is cov- ered to the extent of 1 cm. Heat up the combustion tube moderately to begin with, lighting the center burners first. All joints must be tight, as will be indicated by bubbles passing through the NaOH solution. When the tube is hot, connect the inlet tube of the oxygen bottle to the water tap, so that as water enters, oxygen will be forced slowly over the heated charcoal. Regulate the size of the stream so that, it takes from 1015 minutes to fill the bottle with water. Collect two or three bottles of carbon monoxid over water as it escapes from the apparatus. When the oxygen bottle is full of water, shut off the water, disconnect the combus- tion tube at both ends, and turn off the gas in the furnace. (CAUTION : Carbon monoxid is poisonous. Avoid breathing the gas !) Note the color and odor of the gas and ascertain whether it will burn and support combustion. Describe the flame produced. Introduce 25 com. of lime water into a bottle full of carbon monoxid and shake. Is there any reaction ? How could you tell the difference between carbon monoxid and carbon dioxid? Set fire to this same bottle of gas and shake the lime water with the products of combustion after the flame has gone out. What hap- pens ? To what does carbon monoxid burn ? * Ordinarily charcoal has not been distilled at a sufficiently high tem- perature to remove all volatile material. Before performing this experi- ment it is well to heat the charcoal in the combustion tube in the furnace while passing a slow current of hydrogen through the tube. In this way considerable tarry matter will be removed. EXPERIMENTS 89 Discussion. When oxygen and carbon come together inside the combustion tube, the latter burns just as it does in air, forming carbon dioxid. As this gas passes over the hot carbon it is reduced to carbon monoxid. The sodium hydroxid wash bottle is to remove any un- changed carbon dioxid. Write equations indicating all reactions taking place. Explain in detail how in a similar way carbon monoxid is produced by coal stoves or charcoal braziers, sometimes causing death to the inmates of the house. If carbon monoxid is burned, is this danger removed ? EXP. 48. BURNING AND SUPPORTING COMBUSTION Instructor's Experiment Materials. Wooden splints. Apparatus. A piece of moistened cardboard having a hole in the center, placed on top of a lamp chimney fitted with a stopper pierced by two tubes as shown in Fig. 30. The tube A is wider and shorter than 6r. Clamp and ring stand. Procedure. Support the chimney in a ver- tical position by means of a clamp and ring stand. Connect the- tube 6r to a gas jet and allow illuminating gas to flow at full pressure into the apparatus for a moment. Then turn the gas partly off and light it as it escapes " ^ " A from the hole in the cardboard. Thrust a lighted wooden splint up into the tube A. Describe and explain what happens. What difference is there in the chemical reaction taking place within and without the chimney ? What other gases which you know might be substituted (a) for the illuminating gas ; () for the air ? Under what conditions is it said that a substance burns 90 LABORATORY MANUAL IN CHEMISTRY and another supports combustion ? Under what condi- tions could you reverse the statement ? EXP. 49. FLAMES Materials. Powdered charcoal. Piece of cardboard 10-15 cm. square. HNO 3 . Apparatus. Bunsen burner. Copper wire. Blowpipe, or glass tube 50 cm. long from which to make it. Short piece of glass tube. (&) Why a flame gives light. 1. Notice the blue flame of a Bunsen burner. Does it give considerable light ? 2. Hold a piece of wire or glass tube in the flame, and notice how it emits light as it becomes hot. What would be the effect on the luminosity of the flame if it should become filled with hot solid particles ? By knocking to- gether two blackboard erasers, fill the flame with fine dust and note the effect. Throw some powdered char- coal into the flame and note the effect. 3. Close the air holes at the bottom of the Bunsen burner and notice the change in luminosity of the flame. Are there any visible solid particles which can cause it to emit light? Hold in the flame a cold glass tube. What solid material is deposited? Could it have been the source of the light of the flame ? What becomes of it when the flame is not interfered with? From what is it formed in the flame? Why is an ordinary flame luminous ? (5) The structure of a flame. 1. Note the structure of a Bunsen flame as shown in Fig. 31. EXPERIMENTS 91 2. Using a Bunsen flame with a sharp inner cone, Gr, about an inch high, hold a piece of cardboard in the center of -the flame, first vertically, resting the cardboard on the top of the burner tube ; secondly, horizontally, about an inch above the top of the tube. As soon as the cardboard begins to char, remove it quickly from the flame before it takes fire. The charred outlines are cross-sections of the flame, indicating the hotter parts. 3. Prove that the inner cone, 6r, consists of unburned gas by holding a glass tube in it as shown in Fig. 32, and light the gas as it issues FlG from the tube. 4. Clean a piece of copper wire by dipping it in HNO 3 for a moment, then washing in water. Hold one end of this wire in the top of the flame and explain why it turns black. Lower the wire to a point just above the inner cone and observe and explain how the original coppej 1 color returns. Remove the wire from the flame and note how the hot copper turns black in the air before it cools. Explain. (c) The blowpipe flame. If one is not already available, make a piece of glass tubing of the size and shape shown in D, Fig. 5, and draw out the shorter end as shown in Fig. 3. Cut the slender part straight across so as to form a tip with an opening not larger than the diameter of a pin. Thus you have made a blowpipe. Preserve it for use in later experiments. Turn down the gas in a Bunsen burner until a yellow flame about 4 cm. high results. Hold the blowpipe as 92 LABORATORY MANUAL IN CHEMISTRY FIG. 33. shown in Fig. 33, and blow gently. When the breath is nearly ex- hausted, use the cheeks as a bellows while in- haling a fresh breath through the nose. With a little practice a steady, narrow, very hot flame may be obtained. Note that the blowpipe flame has the same structure as the blue Bunsen flame. The oxidizing flame may be increased in size and the reducing flame diminished by blowing somewhat stronger, and vice versa. EXP. 50. HYDROCARBONS Materials. Kerosene. Candle. Cobalt chlorid solution. Calcium carbid, CaC 2 . Lime water, Ca(OH) 2 . Red lit- mus paper. Gasoline or benzine. Lard, tallow, or but- ter. Filter paper. Apparatus. Small flask with stopper. Two wide-mouth bottles. Glass plate. Two watch glasses or evaporating dishes. (#) Composition. Procedure. 1. Fill a small flask full of cold (ice) water and cork it tightly. Wipe the flask dry and hold it over the flame of burning gas, kerosene, and a candle. Wipe off the moisture in each case with a piece of cobalt chlorid test paper. What is indicated in each case ? How was it formed ? Where must the hydrogen have come from, the air or the burning material? Outline a general EXPERIMENTS 93 method for ascertaining whether a burning substance contains hydrogen. 2. Hold a piece of cold glass tubing in the yellow flame of gas, kerosene, and a candle. What is deposited in each case ? The common gaseous and liquid fuels consist almost wholly of the two elements indicated. What are the final products of combustion when carbon and hydrogen burn ? Write equations indicating the products formed when illuminating gas (consisting mainly of CH 4 and H 2 ) burns. Write a similar equation for the burning of kero- sene, assuming it to have the formula C 10 H 22 . (5) Common gaseous hydrocarbons. 1. Fill a wide-mouth bottle one seventh full of illumi- nating gas by displacement over water. Raise the bottle from the water for a moment and allow air to displace the remaining water. Cover with a glass plate and stand upright on the table. Remove the plate and bring a flame to the mouth of the bottle. What happens ? Why does the gas explode now though it burns quietly in the burners ? 2. Fill a test tube and invert in a dish of water. Drop a small piece of calcium carbid into the dish and quickly collect the liberated acetylene. Note its odor. Close the test tube with the thumb and bring to a flame. Describe how acetylene burns. What is deposited by the flame ? Calculate the percentage composition of acetylene and of methane, CH 4 , the chief constituent of illuminating gas, and see if you can get an idea why one deposits more soot than another. Test the water left in the dish with red litmus paper. Complete the equation and figure out what is present. CaC 2 + 2 H 2 O->C 2 H 2 + 94 LABORATORY MANUAL IN CHEMISTRY (c) Common liquid hydrocarbons. CAUTION: Keep the bottles containing gasoline and benzine away from all flames ! 1. Pour 1 ccm. (25 drops) of kerosene into a watch glass or evaporating dish and the same volume of gasoline or benzine into another and note the time it takes each to evaporate. Which is the more volatile? 2. Pour not more than 25 drops of gasoline or benzine into a wide-mouth bottle, shake well, stand upright on the table and bring a flame to the mouth of the bottle. Explain what happens. Treat similarly 25 drops of kerosene and explain the difference in the results. Why is it that explosions happen so frequently with benzine and gasoline ? 3. Try the solubility of fats, such as lard, tallow, or butter, in benzine or gasoline. Why are these liquids used in " dry cleaning " ? EXP. 51. ALCOHOL AND ACETIC ACID BY FERMENTA- TION Materials. Brown sugar, or sugar solution from Exp. 44. Yeast cake. Sodium acetate, NaC 2 H 3 O 2 . Cone. H 2 SO 4 . Alcohol, C 2 H 5 OH. Lime water, Ca(OH) 2 . Apparatus consisting of a liter flask fitted with an exit tube leading into a small flask used as a wash bottle. This wash bottle containing lime water is protected from the air by having its exit tube dip into water in a test tube. Distillation apparatus as shown in Fig. 18. Evaporating dish. Procedure, (a) Alcohol With a little water rub into a thin paste a quarter of a cake of yeast and add it to the sugar solution used in EXPERIMENTS 95 Exp. 44, adding more sugar until you have about 50 g. in 500 com. of water. Set up the apparatus as directed above, placing the sugar solution in the large flask and about 50 ccm. of lime water in the small flask. Add just enough water to the test tube to cover the end of the exit tube. Allow to stand in a warm place (25-30 C.) for about a week. Fermentation is soon indicated by bubbles of gas ap- pearing in the sugar solution and later passing into the lime water r What is the gas liberated, judging by the reaction in the lime water? (If no reaction is noted, the apparatus leaks.) Leaving the sediment in the bottom of the fermentation flask, decant two thirds of the liquid, and distill it at as low a temperature as possible until about 20 corn, of dis- tillate are obtained. This should consist of alcohol mixed with some water. A second distillation and collection of the first half of the distillate will reduce the proportion of water, which may be removed completely by allowing the mixture to stand for some time over quicklime. This treatment will ordinarily not be necessary to get evidence of the presence of alcohol by the following tests. Pour the distillate into an evaporating dish and dip a piece of filter paper in it. Set fire to the paper, drop it into the dish, and note the character of the alcohol flame. If the filter paper will not take fire, too much water is present. Pour the distillate into a test tube, warm nearly to boiling, and bring the mouth of the tube to a flame. The alcohol will be volatilized (b. p. 78) and burn at the mouth of the tube. (5) Acetic acid. 1. Allow the remainder of the mixture in the fermen- tation flask to stand open to the air for several weeks, 96 LABORATORY MANUAL IN CHEMISTRY rioting the odor, and testing with blue litmus from time to time. The characteristic sour smell of acetic acid, the active constituent in vinegar, will develop eventually. 2. Add 5 ccm. of cone. H 2 SO 4 to 1 g. of any acetate, and warm. Note the sour odor of the acetic acid that is liberated. Add 3 ccm. of alcohol and warm again. Note the sweet odor of ethyl acetate. Both of these reactions are used as tests for acetates. Complete the equations : 2 NaOOC.CH 3 + H 2 SO 4 - - + - EXP. 52. SOAP Materials. Lard, tallow, or cottonseed or olive oil. Solid NaOH; also solution. Alcohol. HC1. Apparatus. A porcelain dish and ring stand. Procedure. In the porcelain dish dissolve 2 g. of NaOH in 20 ccm. of water, add about 10 g. of the fat and 20 ccm. of alcohol, and boil gently until the odor of alcohol is gone and the contents of the dish is a pasty mass. The alcohol takes no part in the chemical action, but serves to dissolve both the fat and the sodium hydroxid, so that they act more rapidly on each other. In practical soap-making no alcohol is used. Complete the equation, and write the name of each substance beneath its formula : NaOOC.C 17 H 35 What is soap, stated in chemical terms ? Do you see any similarity between the reaction by which soap is made and the reaction of alkalies on ammonium salts (p. 78) ? Dissolve some of the resulting substance in warm water and test it with the fingers. Does it appear to be soap ? EXPERIMENTS 97 To some of the soap solution add HC1, and shake vig- orously. The curdy substance that forms is a mixture of stearic with other organic acids. Remove the curdy ma- terial to a test tube, add NaOH solution, and warm. Explain why the precipitate dissolves, and what is formed. EXP. 53. CONSTITUENTS OF FOODS Materials. Cottonseed or olive oil, or lard or butter. Corn meal. Raw egg. Hard boiled egg. Meat. Milk. Nuts. Cheese. Peas or beans. Starch. Flour. Bread. Cane sugar. Glucose or some sirup. Fruit. Potato. Vegetables. Filter paper, cotton, linen, hemp, silk, wool. Mixed cotton and woolen goods. Ether or benzine. H 2 S0 4 . HN0 3 . NaOH. NH 4 OH. Water solution of iodin. Fehling's solution made from tablets or prepared by dissolving 9 g. of copper sulfate crystals, 45 g. of Rochelle salt, and 20 g. of sodium hydroxid in 1000 ccm. of water. Apparatus. Unglazed paper. Litmus paper. Test tubes. Beaker. Funnel. Watch glass or evaporating dish. Porcelain crucible. Pipestem triangle. Procedure . (a) Fats. 1. (CAUTION: Keep ether or benzine away from flames!) To an eighth of a test tube full of corn meal, add 10 ccm. of ether or benzine, cork, and allow to stand 10- 15 minutes. Then filter into a watch glass or evaporating dish and stand in a draught of air to evaporate. Note what is left. Does it seem to be a fat or oil? This method is used as a test for fat. 2. A simpler method of detecting considerable fat is as follows: Put a drop of fat on a sheet of unglazed paper, hold to the light, and note the effect. Press a piece of the 98 LABORATORY MANUAL IN CHEMISTRY yolk of hard-boiled egg upon the paper; after a moment scrape it off and hold to the light as before. Does yolk give a test for fat? Warming will sometimes help this test by melting the fat contained in the substance. 3. Test 2 or 3 other foods for fat, different students using different foods. (5) Carbohydrates. 1. Sugar. Examine and taste glucose, noting its proper- ties. It is difficult to crystallize and is not usually seen in solid form. Most sirups consist mainly of glucose. Heat 10 ccm. of Fehling's solution to boiling, add a little glucose, boil again, and note the result. This pro- cedure is used as a test for sugar. (Several sugars do not give this test, though the common ones do, when properly treated.) If much sugar is present, it can be detected by the taste. Examine and taste cane sugar, noting its properties. It crystallizes readily. Heat 10 ccm. of Fehling's solution to boiling as before and add a few grains of cane sugar. Does it give the test ? Dissolve 1 g. of cane sugar in 10 ccm. of water, add 1 drop of H 2 SO 4 and boil for 5-10 minutes. Then add 10 ccm. of Fehling's solution and boil again. Does it give the test for sugar now ? Test 2 or 3 foods for sugar, boiling with acid if it does not give the test without this treatment. When boiled with any acid, cane sugar is converted into glucose, and levulose, a body resembling glucose closely. Explain how a food may taste sweet, yet not give Fehling's test for sugar until after it is boiled with acid. In making taffy, caramels, butter scotch, etc., what is the use of the vinegar or other acid added before boiling ? If you wanted the candy to "sugar" quickly, i.e. eryss- EXPERIMENTS 99 tallize well, would you boil the mixture with vinegar or other acid ? Why ? Fehling's solution consists essentially of cupric oxid dissolved in a solution of an alkaline tartrate. When boiled with glucose the cupric oxid, CuO, is reduced to cuprous oxid, Cu 2 O, which is not soluble in the tartrate solution and is precipitated as a red powder. 2. Starch. Notice the properties of starch. Moisten it with a water solution of iodin and describe the result. Grind 1 g. of starch to a fine powder, make into a thin paste with 10 ccm. of water, then pour the mixture into 100 ccm. of boiling water and boil 5 minutes.. Cool a por- tion of the boiled starch paste in water and then add a drop of iodin solution. Result? Does the iodin produce a more striking effect on boiled starch than when it is not boiled ? The blue color given by iodin is a test for starch. Heat destroys the color. Test two or three foods for starch, both before and after boiling. 3. Cellulose. Examine filter paper, cotton, linen, hemp, etc., and note the properties of cellulose, especially its toughness. Note how readily it burns when dry, without fumes or much smoke and without swelling up. The fibrous matter in vegetable material is cellulose. Wood and grass contain much, sometimes also celery and parsnips. Other vegetables contain little unless they have become "pithy," i.e. full of cellulose. It is not digested by human beings, hence is of no value as a food con- stituent. Many animals utilize it as food, however. (c) Proteid. 1. Heat some silk, wool, meat, peas or beans and notice how the material swells up as it burns. Note the smoke and the odor produced. Compare with cellulose. 100 LABORATORY MANUAL IN CHEMISTRY 2. Heat one of the above in a test tube, noting the odor produced. Hold a piece of red litmus in the fumes in the tube. What happens ? Explain why. 3. Shake a little albumen (raw white of egg) with water in a test tube. It goes into solution, does it not ? (Many proteids are soluble in water.) Heat the mixture to boiling and note result. Proteids are coagulated by boil- ing. What is the scum that forms when milk, meat, and many vegetables and fruits are boiled ? This is frequently rejected. Do you think it contains nutrient material ? 4. Warm some of the white of a hard-boiled egg with HNO 3 for a moment, pour off the acid into another test tube, and note the color produced. Add NH 4 OH to the egg and note the effect. The yellow color produced by nitric acid is a test for proteid. 5. Test 2 or 3 other foods for proteid, different students using different materials. (d) Mineral matter. (Hood.) Heat some one of the foods you have been testing in a porcelain crucible without cover over the Bunsen flame until the black color due to carbonization has disappeared. Is there much ash left ? An incombus- tible residue left after burning is a test for mineral matter. (e) The amount of water contained in a substance may be determined by heating in a drying oven to 105 C. for several hours. After discussion in the class room, record the results obtained by the different students as follows: FOOD FAT SUGAR STARCH PROTEID MINERAL WATER Potato None None Much Little Little Much Clothing. How could you tell the difference be- tween linen or cotton on the one hand and silk or wool on the other by burning each ? Boil a little cotton cloth, EXPERIMENTS : >01 all wool, and a mixed wool and cotton goods one aftei another for 5 minutes in NaOH solution. What is the result. Outline another method of distinguishing be- tween wool and cotton. EXP. 54. THE HALOGEN GROUP Materials. Powdered fluorspar, calcium fluorid, CaF 2 . Salt, NaCl. Potassium bromid, KBr. Potassium iodid, KI. Cone. H 2 SO 4 . Manganese dioxid, MnO 2 . Paraffin. Apparatus. Test tubes. Lead dish. Glass plate. Procedure, (a) Hydrids of the halogens. Place 1 g. of calcium fluorid in a test tube, add 3 ccm. of cone. H 2 SO 4 , and note what happens. Warm if necessary to hasten the reaction. Treat in the same way 1 g. each of sodium chlorid, potassium bromid, and potassium iodid in separate test tubes. Blow across the mouth of each tube. In each case what causes the fuming? Hold blue litmus in the fumes. What similarities do you observe in the four reactions ? Write equations showing what is formed in each case. Does the mixture in any of the tubes become colored ? If so, what colors are produced and which one changes most quickly? This change is due to oxidation of the hydrogen compound first formed by air or H 2 SO 4 . To increase this effect, add a pinch of manganese dioxid to each test tube and note what happens in each case. To prevent fumes getting into the room, wash out the test tubes as soon as the results are noted. Tabulate your results as follows : COMPOUND OXIDIZED BY AIR OXIDIZED BY MnOj STABILITY HF Not at all Not at all Greatest HC1 HBr HI 102 IABOP.ATORY MANUAL IN CHEMISTRY Hydrogen fluorid is not affected by the most vigorous oxidizing agents. Hydrogen chlorid is oxidized by strong oxidizing agents, hydrogen bromid by mild oxidizing agents, and hydrogen iodid is readily oxidized even by the air. Write equations indicating the products formed in each case. (5) Etching glass ~by hydrofluoric acid. 1. Put a drop of cone. H 2 SO 4 on a piece of glass, sprinkle into it a pinch of powdered fluorspar, and after some minutes note the action of the liberated hydrofluoric acid on the glass. 2. Warm a glass plate about 10 cm. square and cover one side of it with a thin coating of paraffin. Through this wax, when cold, scratch letters or figures with a blunt instrument, taking care that the lines are not too fine, and that the wax is removed through to the glass. In a lead dish mix about 5 g. of powdered fluorspar with enough cone. H 2 SO 4 to make a thin paste, lay the glass plate face down on the dish (see Fig. 34), and allow the exposed places to be acted upon for 24 hours by the fumes of hydrofluoric acid. Scrape off the wax as much as possible, removing the last of it with a cloth moistened with alcohol or benzine (Avoid flames !) and note how the glass is etched. EXP. 55. BROMIN Materials. Bromin water (Br 2 ) containing a little liquid bromin at the bottom of the bottle. Chloroform,* * Carbon disulfid, CS 2 , may be substituted for chloroform, though it should be distilled to render it colorless. Carbon disulfid must be kept away from all flames. EXPERIMENTS 103 CHClg. Alcohol, C 2 H 6 OH. Colored calico. Potassium bromid (KBr) solution. Chlorin water, C1 2 . Apparatus. Test tubes. Procedure, (a) Examine bromin water and state the properties of the liquid bromin at the bottom of the bottle. Does bromin appear to be considerably soluble in water? Cautiously smell of the solution but avoid inhaling much of the vapor, as bromin attacks the membranes of the eyes, nose, and throat even more than chlorin does. Inhaling the fumes from a handkerchief moistened with alcohol will partially overcome the effects. Allow a piece of colored calico to lie in bromin water for some time. Do you note any bleaching action similar to chlorin? (5) 1. To 10 com. of water in a test tube add about 2 ccm. of chloroform, shake thoroughly, then allow the tube to stand for a few moments. Are the liquids apparently soluble in each other? Add 2 ccm. of bromin water, shake again, then stand as before. Judging by the color, where is the bromin, in the water or dissolved in the chloroform? The fact that bromin will collect in and give color to chloroform is used as a test for free bromin. 2. To see whether bromin in combination with other elements will give this test, add 5 drops of KBr solution to 10 ccm. of water and shake with chloroform as before. The result which you get is typical of all compounds con- taining bromin. Make a general statement covering your results. 3. To the mixture used in (2) add 5 ccm. of chlorin water and shake again. Result ? Do you get a test for free bromin ? What must have set the bromin free ? Complete the following equation : KBr + Cl 2 -> KC1 + - 104 LABORATORY MANUAL IN CHEMISTRY Shake chlorin water with chloroform and see if chlorin possibly gives the same color as bromin. Another method of liberating bromin was used in Exp. 54. Make a general statement covering this method. Outline a method of preparing bromin from KBr based on the experiments you have made. EXP. 56. IODIN Materials. lodin. Alcohol. Carbon disulfid. Chlo- roform.* Starch paste. f Potassium iodid (KI) solution. Chlorin water, C1 2 . Bromin water, Br 2 . Phosphorus. Apparatus. Test tubes. Tile or brick. Pincers. Procedure, (a) Examine iodin and state its physical properties', comparing it with bromin and chlorin. Place a few crystals of iodin in a test tube and heat gently, noting what happens. What condenses on the cool parts of the glass ? Define sublimation. Test the solubility of iodin in water, alcohol, carbon di- sulfid and chloroform, noting the relative degrees of solu- bility and the colors produced. (b) Add a drop of iodin solution to some very dilute starch paste and note result. This is used as a test for free iodin. What other use have you made of this same re- action ? To see whether iodin combined with other ele- ments will produce the same color, add a drop of KI solution to starch paste. Result ? (V) 1. Shake 2 ccm. of chloroform with 10 ccm. of a water solution of iodin. Result ? This procedure is used as a test for free iodin. 2. Shake similarly 2 ccm. of chloroform with 20 ccm. of water containing 5 drops of KI solution. The result is typical of all compounds of iodin. Does iodin combined with other elements give the iodin test? * See footnote, p. 102. t Prepared as directed, p. 99. EXPERIMENTS 105 3. Pour half of the KI solution from (2) into another test tube, add 2 ccm. of chloroform and 5 ccm. of chlorin water and shake thoroughly. Result ? What must have set the iodin free? 4. Add to the remaining KI and chloroform mixture from (2) a few drops of bromin water and shake. Result ? What must have set the iodin free ? Write equations showing the action of chlorin and bromin on potassium iodid. Write an equation showing the action of metals, such as zinc, on acids. Compare this equation with the two preceding equations and see if you can note any similarity in the reactions. (c?) Put a little iodin on a tile or brick, and with a glass rod or pincers press gently upon it a small piece of phosphorus, dried between filter papers. Result ? How did chlorin act with phosphorus ? Bromin acts similarly. Would you say that the halogen elements are very active chemically ? Outline a method for preparing iodin from KI based on the experiments you have made. EXP. 57. SULFUR Materials. Sulfur. Carbon disulfid, CS 2 . Strip of copper foil that will slip into a test tube. Powdered iron. Zinc dust. Apparatus. Test tubes. Test tube holder. Watch glass or small beaker. Magnifying glass. 15 cm. filter paper. Funnel. Beaker of water. Procedure, (a) Physical properties. 1. Examine a piece of ordinary sulfur and note its properties. Shake 1 g. with 3-5 ccm. of carbon disulfid for 5-10 minutes, pour off the liquid into a small beaker or watch glass and allow to evaporate. (Keep carbon 106 LABORATORY MANUAL IN CHEMISTRY disulfid away from flames !) Make a sketch of the crystals as seen under a lens. This is rhombic sulfur. 2. Fold a 15 cm. filter paper and place it in a small funnel. Fill a test tube about half full of sulfur and melt it at as low a temperature as possible by holding it over a flame and shaking constantly. Pour the melted sulfur into the filter paper in the funnel and watch it cool. As soon as a few crystals have formed, pour out upon a pan the sulfur which is still melted. Open the filter paper, examine and draw the crystals of monoclinic sulfur thus formed. Are they clear and transparent? Keep them until the next exercise and note any change. 3. Melt a half test tube full of sulfur as before, and heat until it boils, noting the changes of color that occur. From time to time during the heating, tilt the test tube and note the changes in viscosity indicated by the readi- ness with which it flows. Note the color of sulfur vapor and pour the boiling liquid in a thin stream into a beaker of water. Where the sulfur vapor comes in contact with the cold beaker and surface of the water, note and describe the " flowers of sulfur " which form. Examine the properties of the liquid sulfur suddenly cooled by the water, noting its color and hardness and whether it is elastic or brittle. Keep this plastic sulfur until the next exercise and see if there is any change in properties. State in detail the changes in properties of sulfur ac- companying a change in temperature. (6) Chemical properties. 1. Burn a piece of sulfur and cautiously note the odor of the gas produced. State in chemical terms what you mean by the " odor of burning sulfur." 2. Heat 5 g. of sulfur to boiling in a test tube until sulfur vapor fills the tube. Warm a strip of copper foil EXPERIMENTS 107 in the burner and thrust it far into the sulfur vapor, noting carefully what happens. After a minute or two, withdraw the strip and examine the properties of the copper sulfid that has formed. 3. Recall or repeat the experiments showing how iron and zinc combine with sulfur, Exps. 2(d) and 4(e). Would you say that sulfur is chemically active at ordi- nary temperatures ; at high temperatures ? Write equa- tions for the four reactions noted above. Compare the action of sulfur and of oxygen on these metals. EXP. 58. HYDROGEN SULFID, H 2 S Materials. Iron sulfid, FeS. Cone. HC1. Hydrogen peroxid, H 2 O 2 . Bromin water. Solutions of copper sul- fate, CuSO 4 ; arsenic chlorid, AsCl 3 * ; antimony chlorid, SbCl 3 ; stannous chlorid, SnCl 2 ; zinc sulfate, ZnSO 4 . Apparatus. A generator such as was used in preparing hydrogen, Fig. 13, but the gas must be collected by downward displacement and not over water. Glass rod or piece of porcelain. Test tubes. Strip of copper. Silver coin (dime). CAUTION : Hydrogen sulfid is a poisonous gas, the first effects being dizziness and headache. Avoid breathing it. As an antidote inhale chlorin from a handkerchief on which chlorin water has been sprinkled ; or add HC1 to a solution of " chloride of lime " and inhale the fumes. Procedure, (a) Preparation. Fit up the generator as shown in Fig. 13. Put 10-20 g. of iron sulfid in the bottle and through the thistle tube add about 25 ccm. of cone. HC1, diluted with an equal volume of water. Allow the gas to bubble into 100 ccm. of water in a beaker until the water smells strongly of hydrogen sulfid ; * Made by dissolving As 2 O 3 in HC1. 108 LABORATORY MANUAL IN CHEMISTRY then collect 2-3 bottles by downward displacement. Add cone. HC1 through the thistle tube if necessary to hasten the action. Complete the equation : FeS + HC1 -> H 2 S + . (6) Physical properties. Note the color, odor, and taste of hydrogen sulfid. Is it soluble in water ? (Smell of the water into which the gas has been passing before answering this question.) Test the action of hydrogen sulfid water on blue litmus paper and explain. (tf) Chemical properties. 1. Does hydrogen sulfid support combustion? Does it burn ? Light the gas as it escapes from the generator and cautiously smell the fumes. What is one product of com- bustion of H 2 S ? Hold a cold glass rod or piece of porce- lain in the flame. What deposits on it? Where did it come from? Why do you get no deposit when the gas burns freely? Compare the formation of a deposit here with the deposit of soot in an ordinary flame. 2. Add a few drops of hydrogen peroxid to 10 ccm. of H 2 S water. Explain what happens. Is H 2 S an oxidizing or a reducing agent? Complete the equation: H 2 2 4- H 2 S -> S + - 3. Add a few drops of bromin water to 10 ccm. of H 2 S water and explain what happens. All the other halogen elements will act similarly. Complete the equation : Br 2 + H 2 S -> S + 4. Add to 10 ccm. of H 2 S water a few drops of copper sulfate solution and describe what happens. In a similar way add arsenic chlorid, antimony chlorid, stannous EXPERIMENTS 109 chlorid, and zinc sulfate, to separate portions of H 2 S water. Describe the sulfids formed and complete the equations : CuSO 4 + H 2 S -> CuS + - AsCl 3 + H 2 S -+ As 2 S 3 + - SbCl 3 + H 2 S ->- Sb 2 S 3 + - SnCl 2 + H 2 S -> SnS + - ZnSO 4 + H 2 S -> ZnS H -- 5. Hold a strip of copper and a silver coin in H 2 S water and note the effect. Complete the equations : Cu + HS -> CuS + - No considerable action of this kind takes place except when an oxidizing agent (such as air) is present to com- bine with the nascent hydrogen as it is liberated. This action is mainly responsible for the tarnishing of silver. The odor of hydrogen sulfid and the blackening of silver caused by its solutions are tests for hydrogen sulfid. EXP. 59. SULFUR DIOXID, S0 2 , AND SULFUROUS ACID, H 2 S0 3 Materials. Sulfur. Wooden splint. Flowers, or piece of calico. Solutions of potassium permanganate, KMnO 4 ; sodium sulfite, Na 2 SO 3 ; barium chlorid, BaCl 2 . Litmus paper. HC1. NaOH. Charcoal or copper. Cone. H 2 SO 4 . Apparatus. Combustion spoon. Wide mouth bottle. Oxygen generator as shown in Fig. 9 without the pneu- matic trough. Procedure. (a) Preparation ly oxidation of sulfur. 1. Place a piece of sulfur in a combustion spoon, ignite it and lower it into a wide mouth bottle. Cover the bottle and allow the sulfur to burn until the flam'e is 110 LABORATORY MANUAL IN CHEMISTRY extinguished. Note the color, odor, and taste of sulfm dioxid. Will it burn or support ordinary combustion ? Prepare another bottle of sulfur dioxid in a similar way. Moisten a flower or piece of calico, and allow it to stand in the sulfur dioxid for some time. What seems to be the action of sulfur dioxid on coloring matter ? 2. Pour 10-20 com. of water into a bottle and shake it about so that the bottle is wet all over. Burn sulfur above the water in the bottle as before, and shake so that the gas produced may be absorbed. Pour the water from the bottle and smell of it. Is sulfur dioxid soluble in water ? Test the water with blue litmus paper, noting the first and also the latter effects. Is sulfur dioxid an acid anhydrid? Compare the following equation with the action of carbon dioxid on water. SO 2 + H 2 O -> H 2 SO 3 , sulfurous acid. 3. Add NaOH solution, drop by drop, to the sulfurous acid solution until it turns litmus paper blue. Does the solution smell of sulfur dioxid any longer ? Complete the equation and name the product formed. H 2 S0 3 + NaOH->Na 2 S0 3 + (5) Preparation by reduction of sulfuric acid, H 2 SO 4 . 1. Fit up a test tube with an outlet and delivery tube as shown in Fig. 9. Fill the test tube one eighth full of pieces of charcoal or copper, and add 10 ccm. of cone. H 2 SO 4 . Suspend the apparatus from a ring stand and heat with a small flame as the gas is evolved. If white fumes appear above the liquid, moderate the heat immediately. 2. Repeat the experiments of () sufficiently to assure yourself that the same gas is produced in (6) as in (V). 3. Allow the gas to bubble into about 10 ccm. of water EXPERIMENTS 111 in a test tube until it smells strongly of sulfur dioxid. Use this solution for (CO + -- > - + - H 2 S0 4 + Cu->CuO + - -> -- + - (c) The odor of sulfur dioxid and the fact that it will bleach potassium permanganate are used as tests for sulfur dioxid and sulfurous acid. 1. Test part of the solution obtained in (6) by adding a few drops of potassium permanganate solution* What happens ? Do you get a test for SO 2 and H 2 SO 3 ? 2. To a solution of sodium sulfite, add HC1 and note the odor; then add KMnO 4 as in (1). Do you get the same test ? Why is it necessary to add HC1 in (2) but not in (1) ? 3. Add barium chlorid and HC1 to (1) and (2). The formation of a white precipitate is a test for sulfates. Did you get the test ? Permanganates are substances very rich in oxygen which is liberated readily and oxidizes sulfurous acid. Complete the equation: H 2 S0 3 + 0->- EXP. 60. SULFUR TRIOXID, S0 3 , AND SULFURIC ACID, H 2 S0 4 Instructor's Experiment Materials. Scraps of platinum. Cone. HNO 3 and HC1. Asbestos. Cone, solution of sulfur dioxid. Barium chlorid (BaCl 2 ) solution. Apparatus. A 2-liter bottle fitted with inlet and exit tube as used in Exp. 47, connected with a wash bottle which is connected with a glass tube about 30 cm. long filled with asbestos containing finely divided platinum. Test tube. Porcelain crucible. Pipestem triangle. 112 LABORATORY MANUAL IN CHEMISTRY Procedure. Dissolve 0.5-1 g. of old platinum foil or wire in aqua regia, evaporate to 2-3 ccm., then add about 10 com. of water. Shred some asbestos board, soak the shreds in the platinum solution just prepared, and heat to redness in a porcelain crucible or dish. By this treatment the platinum chlorid is decomposed, leaving finely divided platinum deposited throughout the asbestos. Set up the apparatus as directed above, connecting the inlet tube of the large bottle to the water tap, and the outlet tube to the wash bottle which contains a strong solution of sulfur dioxid in water. Loosely fill the center third of the glass tube with the platinized asbestos, sup- port it on a ring stand, and connect it to the exit tube of the wash bottle. Arrange the apparatus so that when water enters the large bottle, air will be forced through the solution in the wash bottle and, mixed with sulfur dioxid, will pass over the platinum. Regulate the stream of water so that about one bubble a second passes through the wash bottle. Note that no interaction between the sulfur dioxid and oxygen takes place at ordinary tempera- ture. When the tube is moderately heated, sulfur trioxid is formed. State what you observe. Rinse out a test tube with water and slip it over the end of the tube con- taining the platinum so that the fumes may come in con- tact with the moisture on the sides of the tube. After a few moments rinse out the test tube with water and test the solution for sulf uric acid. EXP. 61. PHOSPHORUS Materials. Yellow and red phosphorus. Phosphorus pentoxid, P 2 O 5 . HC1. Cone. HNO 8 . Solution of ammo- nium molybdate, (NH 4 ) 2 MoO 4 . Commercial fertilizers. Ferrous sulfate, FeSO 4 . Cone. H 2 SO 4 . NaOH. EXPERIMENTS 113 Apparatus. Tile or brick. Large beaker. Blue lit mus paper. Glass rod. Cobalt glass. Platinum wire. Procedure. (#) Note the physical difference between yellow (observe the cautions given on p. 15) and red phosphorus. Place a little of each upon a tile or brick and touch with a warm glass rod. What happens ? Heat the glass rod and try to ignite the red phosphorus. If you do not succeed, ignite it with a burner. Compare the way red and yellow phosphorus take fire and note the product formed in each case. (5) Dry a piece of phosphorus about the size of a pea, and place it upon a tile or brick. Ignite it, cover with a large beaker and allow to stand until the white " smoke " has settled. What is the " smoke " ? Describe it. Press a moistened piece of blue litmus paper upon some of the deposit. Explain what happens. Allow the de- posit to stand in the air for about an hour and note what happens ; test it now with a piece of dry blue litmus paper and explain why phosphoric pentoxid is one of the best dry- ing agents. Complete the equation : (c) Place about 1 g. of phosphorus pentoxid in a test tube and add a few drops of water. Is the combination with the water vigorous or mild ? Add 10 ccm. of water and boil for 5 minutes. Add one drop of this phosphoric acid solution to 5 ccm. of ammonium molybdate solution to which a few drops of cone. HNO 3 have been added. The formation of a yellow precipitate on standing 5-10 minutes is a test for phosphates. (jot) To 1 g. of commercial fertilizer add 10 ccm. of water and a few drops of HC1, heat to boiling and filter. Test the solution for salts of phosphoric and nitric (p. 72) acids and of ammonium (p. 78) and potassium 114 LABORATORY MANUAL IN CHEMISTRY (p. 126). Does tliis fertilizer contain all the foods neces sary for a plant ? EXP. 62. PHOSPHIN, PH 3 Instructor's Experiment Materials. Solid NaOH or KOH. Yellow phosphorus. Apparatus. As shown in Fig. 35. Procedure. Put about 50 g. of solid NaOH or KOH, 200 ccm. of water and 23 pieces of phosphorus about the size of a pea in a quarter or half liter flask and set up the apparatus as shown in Fig. 35. Connect the inlet tube of the flask with the gas pipe and allow gas to flow at full head into the flask for a minute until the air is replaced ; then turn down the gas so that about 1 bubble in 5 seconds issues from the exit tube. Heat up the solution in the flask until it nearly reaches the boiling point, and main- tain this temperature by a small flame. Phosphin and other hydrids of phosphorus will be generated and escape through the water into the air. Describe what happens. What can you say about the kindling temperature of some of the gases formed ? What difference do you notice between PH, and NH? What is the "smoke" o o formed by burning PH 8 ? Why is it necessary to remove the air from the flask ? What would happen if air got into the flask? FIG. 35. EXPERIMENTS 115 Before taking the apparatus apart, allow the liquid to cool and sweep out all phosphids by turning on the illu- minating gas full head for a moment. Pour out the solution, wash any remaining phosphorus with water and replace it in the phosphorus bottle. EXP. 63. ARSIN, AsH 3 , AND STIBIN, SbH 3 Instructor's Experiment Materials, l^inc. HC1. Solutions of any arsenic com- pound, of any antimony compound, and of " chloride of lime." Apparatus. 2 hydrogen generators. 2 clay pipe stem jets for burning the gas. 3 porcelain plates or evaporat- ing dishes. Procedure. Start both generators and ascertain that all air has been driven from each apparatus by testing the purity of the gas as directed on page 36. When the gas collected burns quietly, replace the delivery tube with the pipe stem and ignite the hydrogen as it issues. When the hydrogen burns quietly, introduce into one generator through the thistle tube a few drops of any arsenic com- pound and into tho other the same amount of any antimony compound. Describe the changes in the flames. Any soluble compound of arsenic or antimony is re- duced by the nascent hydrogen to arsin and stibin. Write equations for this change, assuming that you started with AsCL and SbCL. o o Move a porcelain plate slowly about in the flame in which arsin is burning and describe the effect. Get a similar deposit from the stibin flame on a second plate. This procedure is known as the Marsh test for arsenic and antirt^ony. On a third plate trace the symbol Sb by means of the stibin flame and then obliterate it by means of the deposit from the arsin flame. 116 LABORATORY MANUAL IN CHEMISTRY Treat all three plates with " chloride of lime " solution and state the results. What differences do you notice between AsH 3 and SbH 3 on the one hand and NH 3 on the other? Write equations showing what is formed when arsin and stibin burn. As 2 O 3 and Sb 2 O 3 are white solids ; do you get any evidence of them ? When the flame is cooled, elementary arsenic or antimony is deposited. Compare with the de- posit of sulfur from burning H 2 S and of carbon from H 4 C and other hydrocarbons. The deposit of arsenic and antimony cannot be distin- guished with certainty except by chemical means. Ar- senic is readily dissolved in hypochlorites, being oxidized to arsenic pentoxid, which unites with water to form ar- senic acid, H 3 AsO 4 . Antimony is not easily oxidized by this reagent, hence remains on the plate. Complete the equations and compare with phosphoric acid (p. 113). _ As + O -> As 2s + H 2 -* H 3 AsO 4 EXP. 64. ELEMENTS THAT ACT BOTH AS ACID- FORMERS AND BASE-FORMERS Materials. Solutions of lead nitrate, Pb(NO 3 ) 2 ; sodium carbonate, Na 2 CO 3 ; sodium sulfate, Na 2 SO 4 ; potassium chromate, K 2 CrO 4 ; stannous chloride, SnCl 2 ; zinc sul- fate, ZnSO 4 ; aluminum sulfate, A1 2 (SO 4 ) 3 ; antimony chlorid, SbCl 3 . Arsenic oxid, As 2 O 3 . Bits of tin, zinc, and aluminum. NaOH. KOH. NH 4 OH. HC1. Procedure, (a) Lead as a base-former. Dilute 10 ccm. of lead nitrate solution to 50 ccm. with water. To 5 ccm. portions of this solution add a few drops of the reagents specified : (1) NaOH ; (2) Na 2 CO 3 ; (3) Na 2 SO 4 ; (4) K 2 CrO 4 . Note the result in each case. EXPERIMENTS 117 Write equations and name each lead compound formed. What uses are made of any of these compounds ? Acting as a base-former, lead unites with what kind of radicals ? (5) Lead as an acid-former. 1. To 5 ccm. of your lead nitrate solution add NaOH until the precipitate, first formed, redissolves. Write equa- tions showing what lead compound you now have in solu- tion. Name it. Test this solution with a drop of each of the reagents used in (a). Do you get any of these indications of the presence of lead ? Why not ? Lead as an acid-former unites with what kind of elements ? 2. Use KOH as in (1). Does it act similarly ? 3. Use NH 4 OH as in (1). Does it act similarly ? What makes lead act as an acid-former? (NH 4 OH is not sufficiently strong as a base to cause any element to act as an acid-former.) (4 H 8 BO P + 3 1 () 1. Place some of the boric acid in an evaporating dish and add 3-5 ccm. of alcohol. Set fire to the alcohol and note the color of the flame. If the color is not distinct, soak a shred of asbestos in the mixture and heat in the hottest part of a Bunsen flame. This green flame is used as a test for boric acid. 120 LABORATORY MANUAL IN CHEMISTRY 2. Dissolve a crystal of borax in a little water and set free the boric acid by adding a little HC1. Dip a piece of turmeric paper in the solution and dry it by placing it on the outside of a beaker or test tube of boiling water, where it will be heated to 100 but not much higher. The red color which appears on drying is a test for borates. (With dilute solutions it may be necessary to wet the turmeric paper and dry it repeatedly to get a good test.) Moisten the red paper with an alkali and note the change of color. Will HC1 restore the color ? (V) Rotate one end of a piece of glass tubing in a Bunsen flame and just as the glass is running together insert a platinum wire about 5 cm. long heated red hot. The glass tube will serve as a handle and prevent loss of the wire. Make a loop in the end of the platinum wire about. 2-3 ram. in diameter by wrapping the wire once around the point of a lead pencil. Heat the loop and while hot press it against a small crystal of borax, thus causing it to adhere. Heat the borax in the hottest part of the Bunsen flame or better in the flame of a blowpipe, noting how it swells up as the water in the crystals boils away. Note also the clear bead finally produced. While this bead is hot, press it against a mere trace of a cobalt compound and heat again. Note the color produced. To remove the bead, heat it red hot and shake it out of the loop or plunge it into water, thus causing it to disin- tegrate. Make a new bead and see that it is colorless. If not* shake out again and start anew. Make similar beads containing manganese, chromium, and iron compounds. Heat all the beads in the oxidizing flame and record the colors produced. EXPERIMENTS 121 EXP. 67. ALUM FROM CLAY Materials. Clay. Cone. H 2 SO 4 . Potassium carbon- ate, K 2 CO 3 . NH 4 OH. Solutions of cobalt nitrate, Co(NO 3 ) 2 , and alum, KA1(SO 4 ) 2 . Apparatus. Evaporating dish. Beakers and funnel. Plaster of Paris block * or piece of charcoal or bark. Procedure, (a) Mix thoroughly 50 g. of dry, finely pulverized clay soil with 30 ccm. of cone. H 2 SO 4 in an evaporating dish, and heat for 20 minutes (Hood) over a low flame to such a temperature that white "fumes just begin to appear. When cool, pour the mixture into a beaker, add 100 ccm. of boiling water, stir thoroughly, allow to settle, and while still hot decant the liquid as completely as possible into a second beaker. Treat the residue in the same way with 50 ccm. and then with 30 ccm. of boiling water. Heat the combined water ex- tracts to boiling, and add slowly with constant stirring, 12 g. of solid potassium carbonate. After all action has ceased, filter the boiling liquid. Evaporate the filtrate to half its original volume and set aside to cool until the next exercise. Remove the crystals obtained and dry them between filter papers. More crystals may be obtained by further concentra- tion of the remaining liquid. They will not be as pure and may need recrystallization to get them colorless. The composition of clay may be taken as HAlSiO 4 , the reaction on heating with H 2 SO 4 being : 2 HA18iO 4 + 3 H a SO 4 -> A1 2 (SO 4 ) 8 -f SiO 2 -f - - H 2 O In the preceding equation fill in the numbers necessary to make it balance. The effervescence produced on add- * Mix plaster of Paris with one third its weight of water and pour it upon a sheet of paper laid upon the desk. When it has partially hardened, cut it into pieces about 10 x 2 cm. and allow to dry. 122 LABORATORY MANUAL IN CHEMISTRY ing K 2 CO 3 is due to the excess of H 2 SO 4 not used in decomposing the clay. Write the equation for the forma- tion of alum. (5) Dilute 5 ccm. of alum solution with 10 ccm. of water and add NH 4 OH. Notice the character of the aluminum hydroxid precipitated. Heat the mixture to boiling and filter. Heat some of the precipitate with the blowpipe upon charcoal or plaster of Paris and note the character of the aluminum oxid formed. Moisten the alu- minum oxid with a drop of cobalt nitrate and heat strongly again. A blue color is a test for aluminum. (Zinc gives a green color when similarly treated.) (c) Shake some pulverized clay with water and allow the heavier material to settle out for ten minutes. With 100 ccm. of the turbid water mix 5 ccm. of alum solution. Add a piece of litmus paper and make just alkaline with ammonium hydroxid. Note the time it takes this solution to settle clear as compared with some of the water that has not been so treated. This illustrates a method for making turbid water clear, except that the cheaper calcium hy- droxid is used instead of ammonium hydroxid. What causes the clay to settle ? EXP. 68. DYES AND MORDANTS Materials. Pieces of white cotton cloth about 2 by 10 cm. Cone. HC1. NH 4 OH. Solution of Congo Red containing 1 g. of dye, 1 g. of Na 2 CO 3 , and 2 g. of Na 2 SO 4 in each 100 ccm. of water. Solution of alizarin containing 1 g. of dye in each 100 ccm. of water and enough NH 4 OH to make it go into solution. Solution of aluminum sulfate, A1 2 (SO 4 ) 3 . Solution of cochineal * boil 10 g. in 100 ccm. of water. Extract of logwood made by covering logwood with water and bringing it to boiling. Do this four times. Reject first three ; keep fourth. * Cochineal contains carminic acid. EXPERIMENTS 123 Apparatus. Evaporating dish, test tubes, and beakers. Procedure, (a) To remove the " sizing " from the cloth. Add 5 ccm. of cone. HC1 to 100 com. of water in a beaker, place 3-5 pieces of cloth in this solution, and heat to boil- ing; then wash the cloth thoroughly in running water and finally dip in water containing a few drops of NH 4 OH. (5) 1. Dilute 5 ccm. of the Congo Red solution to 50 ccm. with water in an evaporating dish. Keep the solution boiling gently and immerse a piece of cloth in it for 3-5 minutes, stirring constantly. Remove the cloth, wash thoroughly, dry and put in your notebook. Congo Red dyes cotton without a mordant. 2. Dilute 5 ccm. of the alizarin solution to 50 ccm. with water. Boil a piece of cloth in it ; remove, wash, and dry as before. Does alizarin dye cotton without a mordant ? (V) 1. Add a few drops of NH 4 OH to 5 ccm. of a solu- tion of aluminum sulfate. What is precipitated ? 2. Pour 5 ccm. of your alizarin solution into a test tube, dilute with 10 ccm. of water, heat to boiling and add 5 ccm. of aluminum sulfate solution. If a precipitate does -not form immediately because of the NH 4 OH in the alizarin solution, add a few drops of NH 4 OH. Allow to stand until the precipitate settles. Where is the color, in the liquid or in the precipitate ? An insoluble compound formed by the union of a base (or an acid) with a dye is called a lake. 3. Soak a piece of cloth in the aluminum sulfate solution, squeeze it dry and attempt to dye it in your alizarin solu- tion as before. Is the result any better ? Where is the lake in this case ? Aluminum hydroxid acts as a mordant for alizarin; also for other dyes including logwood and carminic acid (cochineal). If you have time, try one of these also. 124 LABORATORY MANUAL IN CHEMISTRY EXP. 69. HARD WATER AND HOW TO SOFTEN IT Materials. Soap cut into pieces about the size of a pea. Solutions of calcium sulfate, CaSO 4 ; sodium carbonate, Na 2 CO 3 ; borax, Na 2 B 4 O 7 ; and sodium phosphate to which 1 g. of NaOH is added for each 5 g. of Na 2 HPO 4 , thus forming Na 3 PO 4 . Lime water, Ca(OH) 2 . HC1. NaOH. NH 4 OH. Litmus paper. Several different kinds of wash- ing powders or "boiler compounds." Marble, CaCO 3 . Ammonium molybdate, (NH 4 ) 2 MoO 4 . Turmeric paper. Apparatus. Carbon dioxid generator (p. 85). Procedure, (#) Hard waters. Dilute 40 ccm. of lime water with 60 ccm. of water, pass in carbon dioxid until the precipitate first formed is re- dissolved. Write equations expressing the change taking place. What substance is in solution ? Call this No. I. Add 20 ccm. of calcium sulfate solution to 80 ccm. of water. Call this No. II. 1. Take half a test tube full of distilled water, add a piece of soap, cover with the thumb, and shake, noting the readiness with which a lather is formed. 2. Treat half a test tube of No. I in the same way. Does it lather readily ? 3. Treat half a test tube of No. II just as in (2). Does it lather readily ? Solutions I and II are typical hard waters. Magnesium salts act similarly to calcium salts and both are commonly present in water. 4. Remove some of the precipitate ("scum ") appearing in (2) and (3) to a watch glass and treat with 2-3 ccm. of water and 5 drops of HC1. The precipitate dissolves, but a new one (stearic acid) forms immediately. Scrape this on to the edge of the watch glass, drain off the liquid, wash with a few drops of water and add 5 drops of NaOH. EXPERIMENTS 125 Does the precipitate dissolve ? Stir it and see it lather. What is in the solution ? What is the " scum " ? 5. Boil half a test tube of No. I. Do you note any change ? Shake with soap as before. Is there any dif- ference now? Explain why. Water that is softened by boiling is called " temporarily hard water." 6. Treat half a test tube of No. II as in (5), answering the same questions. What is the difference between the two hard waters ? Water not softened by boiling is called " permanently hard water." (6) Chemical methods of softening hard water. 1. Add NH 4 OH to half a test tube of I until red litmus turns blue. Shake with soap as before. Does NH 4 OH soften the water? In softening temporarily hard water, any base will act similarly. Usually the calculated amount of lime, the cheapest base, is added to it. Complete the equation : CaH 2 (C0 3 ) 2 -f Ca(OH) 2 -- - 2. Add 2-3 ccm. of sodium carbonate solution to half a test tube of either I or II. Do you note any change ? Shake with soap. Is the water soft ? Write equation. 3. Add 2-3 ccm. of borax solution as in (2). Result? 4. Add 2-3 ccm. of sodium phosphate solution as in (2) Result ? ( Ag 2 CO 3 + 2 NaNO 3 . . * This sodium carbonate must be the purest obtainable. 138 LABORATORY MANUAL IN CHEMISTRY PRECIPITATES PRODUCED BY COLOR OF SALTS K,Cr0 4 (NH 4 ) 2 S NH 4 OH NaOH red red yellow black black black black black white white brown yellow yellow white l white yellow white white Ag Hg ous Hgic Pb yellow olive brown black yellow white blue 1 white 1 white blue white white blue white Bi Cu Cd yellow 2 orange 2 brown 2 yellow 2 white white white white 1 white l white 1 white white white white As Sb Sn ous Sn ic white gray black black white gray green red white x gray green red white green green reddish Al Cr Fe ous Feic black black buff white pink 1 green l buff white l lavender green buff white l red green pink white Co Ni Mn Zn yellow white white white white white white Mg Ba Sr Ca white white white K Na NH 4 1 Soluble in excess. 2 Sometimes difficult to obtain; add drop of HC1 also. SOLUBILITY OF COMPOUNDS Potassium, sodium, and ammonium compounds all soluble in water. Nitrates and acetates all soluble. Chlorids all soluble except silver, mercury (ous), and lead. Sulfates all soluble except barium, strontium, calcium, and lead. Carbonates, phosphates, and borates all insoluble except potassium, sodium, and ammonium salts. Oxids and hydroxids and sulfids all insoluble except potassium, sodium, ammonium, barium, strontium, and calcium. LISTS OF CHEMICALS AND SUPPLIES A liberal allowance for a class of 10 students doing all the experiments. All chemicals are C. P. lib. Acid, acetic, 30% 12 Ib. Acid, hydrochloric, Sp. Gr. 1.19 6 Ib. Acid, nitric, Sp. Gr. 1.42 1 Ib. Acid, oxalic 8 Ib. Acid, sulfuric, Sp. Gr. 1.84 2qt. Alcohol, 95% 1 oz. Alizarin 2 Ib. Alum 1 oz. Aluminum, sheet 8 oz. Aluminum sulfate 1 Ib. Ammonium carbonate 1 Ib. Ammonium chlorid 10 Ib. Ammonium hydroxid, Sp. Gr. 0.9 1 oz. Ammonium molybdate 1 Ib. Ammonium nitrate 1 oz. Antimony chlorid 1 oz. Antimony oxid 1 oz. Arsenious oxid 8 oz. Barium chlorate 8 oz. Barium chlorid 8 oz. Barium nitrate 1 oz. Bismuth chlorid 1 oz. Bismuth oxid 8 oz. Bromin 1 oz. Cadmium nitrate 1 Ib. Calcium carbid 10 Ib. Calcium carbonate, marble chips 8 oz. Calcium carbonate precipi- tated chalk 1 Ib. Calcium chlorid, granules 1 Ib. Calcium fluorid, fluorspar, powder 8 oz. Calcium nitrate 2 Ib. Calcium oxid, lime, in tins 1 Ib. Calcium sulfate, gypsum 2 Ib. Calcium sulfate, plaster of Paris 1 Ib. Carbon disulfid 1 oz. Cochineal, ground 1 Ib. Charcoal, animal. Bone- black. I Ib. Charcoal wood 1 Ib. Charcoal wood blocks 1 Ib. Chloride of lime 1 Ib. Chloroform 4 oz. Chromium sulfate 4 oz. Cobalt chlorid 4 oz. Cobalt nitrate 1 oz. Congo red 1 Ib. Copper, foil, ^ in. 2 Ib. Copper turnings 4 spools Copper wire, Nos. 16, 18, 24, 30. 1 oz. Copper oxid, black powder 3 Ib. Copper sulfate 1 Ib. Ether 1 oz. Fehling's solution tablets 15 packs Filter papers, 4 in. 2 packs Filter papers, 6 in. 1 pack Filter papers, 12 in. 1 oz. Hydrochinon 1 oz. Indigo 4 oz. lodin, resublimed 1 Ib. Iron powder "alkoholized " 2 spools Iron wire, Nos. 16 and 24 1 Ib. Iron chlorid (ic) 1 Ib. Iron sulfate (ous) 2 Ib. Iron sulfid (ous) for H 2 S 1 Ib. Lead, sheet 8 oz. Lead, acetate' 4 oz. Lead dioxid 1 Ib. Lead nitrate 1 Ib. Lead oxid, litharge 139 140 LABORATORY MANUAL IN CHEMISTRY 1 oz. Litmus cubes 25 books Litmus paper, red 25 books Litmus paper, blue 4 oz. Logwood, ground 4 oz. Magnesium, ribbon 8 oz. Magnesium nitrate 4 oz. Magnesium oxid, wet process 8 oz. Magnesium sulfate 2 Ib. Manganese dioxid, powdered 8 oz. Manganese nitrate 8 oz. Manganese sulfate ] Ib. Mercury 4 oz. Mercury chlorid (ic) 4 oz. Mercury nitrate (ic) 4 oz. Mercury nitrate (ous) 4 oz. Mercury oxid 4 oz. Nickel sulfate 1 Ib. Oxone. (Fused sodium per- oxid) 1 oz. Phenolphthalein 1 oz. Phosphorus, red 4 oz. Phosphorus, yellow 1 oz. Phosphorus pentoxid 1 oz. Potassium, metal 8 oz. Potassium bromid 8 oz. Potassium carbonate 3 Ib. Potassium chlorate 1 Ib. Potassium chlorid 4 oz. Potassium chromate 1 Ib. Potassium dichromate 8 oz. Potassium ferricyanid 4 oz. Potassium ferrocyanid 1 oz. Potassium acid sulfate 2 Ib. Potassium hydroxid, sticks 2 Ib. Potassium nitrate 4 oz. Potassium iodid 4 oz. Potassium nitrite 8 oz. Potassium permanganate 8 oz. Potassium sulfate 1 oz. Potassium thiocyanate 1 Ib. Rochelle salt 4 oz. Silver nitrate 4 oz. Sodium, metal 4 oz. Sodium acetate 1 Ib. Sodium carbonate, purest, dry 5 Ib. Sodium chlorid, fine 4 oz. Sodium chromate 2 Ib. Sodium hydroxid, sticks 1 Ib. Sodium nitrate 4 oz. Sodium nitrite 4 oz. Sodium peroxid, powder 8 oz. Sodium phosphate 2 Ib. Sodium sulfate, crystals 8 oz. Sodium sulfite, crystals 2 Ib. Sodium thiosulfate, hypo 8 oz. Strontium chlorate 4 oz. Strontium chlorid 3 Ib. Sulfur 1 oz. Tartar emetic 1 Ib. Tin, granulated 8 oz. Tin chlorid (ous) 1 oz. Tin oxid (ic) 1 sheet Turmeric paper 1 Ib. Zinc, dust 3 Ib. Zinc, mossy 1 Ib. Zinc, sheet 4 oz. Zinc nitrate 4 oz. Zinc oxid, wet process 8 oz. Zinc sulfate MATERIALS TO BE OBTAINED LOCALLY AS NEEDED 4 oz. Baking powders, several dif- ferent kinds 1 Ib, Baking soda 1 pt. Benzine 4 oz. Beans Blue print paper 1 Ib. Borax 4 doz. Candles, Christmas 2 Carbonated water, syphons or bottles INDIVIDUAL APPARATUS 141 4 oz. Cheese 10 yd. Cheesecloth (towels) 4 oz. Coal (soft) 4 oz. Corn meal 4 Ib. Cotton batting | yd. Cotton cloth, colored. | yd. Cotton cloth, white 4 oz. Cream of tartar 1 Egg, raw 1 Egg, hard boiled 4 oz. Fertilizers, several different kinds 4 oz. Flour Fruit 4 oz. Glucose sirup 4 oz. Hydrogen peroxid 1 box Iron picture wire 1 Ib. Iron shingle nails 1 pt. Kerosene 4 oz. Lard Matches, parlor Matches, sulfur 4 oz. Meat 4 oz. Milk 4 oz. Nuts 1 pt. Olive oil 1 Ib. Paraffin 4 oz. Peas 1 Ib. Rock candy 10 sheets Paper, black 10 sheets Paper, writing 1 Potato 4 oz. Starch 1 cake Soap 1 pt. Turpentine 1 Ib. Sugar, dark brown 1 Ib. Sugar, granulated Vegetables 4 oz. Vinegar 1 oz. Wool or felt 4 oz. Washing powder, several dif- ferent kinds 5 Ib. Washing soda 3 Yeast cakes. INDIVIDUAL APPARATUS For class of 10 students. Liberal allowance for breakage has been made. 12 Beakers, 500 ccm. 24 Beakers, 250 ccm. 24 Beakers, 125 ccm. 12 Brashes, test tube 15 Burners, Bunsen with wing tips 12 Calcium chlorid tubes, straight, 1 bulb 12 Capsules for sodium (see p. x) 12 Clamps for condensers 12 Clamps for test tubes 12 Condensers (Liebig), 15 in. 12 Combustion spoons, \ in. bowl 15 Crucibles, porcelain, No. 0, with covers 25 Dishes, evaporating, No. 1 12 Dishes, lead 12 Files, 3-cornered 5 packs filter paper, 9 cm. 5 packs filter paper, 15 cm. 12 Flasks, flat bottom, 500 ccm., with 2-hole rubber stoppers to fit 25 Flasks, flat bottom, 250 ccm., with 2-hole rubber stoppers to fit 12 Flasks, round bottom, 500 ccm., with 1-hole rubber stoppers to fit 12 Flasks, round bottom, 250 ccm., with 1-hole rubber stoppers to fit 12 Frying pans, iron, 5 in. 12 Funnels, 2| in. 5 doz. Fruit jars, pint 50 Glass plates, 3 x 3 in. 12 Glass plates, 6 x 6 in. 10 Glass plates, 3 x 4 in. Cobalt glass 142 LABORATORY MANUAL IN CHEMISTRY 100 ft. Glass tubing, 6 mm. outside diameter. For bending 25 ft. Glass tubing, 3 mm. outside diameter. For stirring rods. 12 Graduates, 25 com. 12 Medicine droppers 12 Mortars with pestles, porcelain, 4 in. 12 Pincers, iron, 4 in. 12 Pipe stems, clay 15 Pipe stem triangles, small 12 Pneumatic troughs (see p. vii) 12 Retorts, 125 com., with ground glass stoppers 50 ft. Rubber tubing, T 3 g in. inside diameter 12 Stand irons with 2 rings 20 doz. Test tubes, soft, 6 x f in. 20 Test tubes, side-neck, 6 x f in. 12 1-hole rubber stoppers to fit 24 Test tubes, ignition, 6 x f in. 12 Test-tube holders, brass wire 12 Test-tube racks for 12 test tubes 15 Thistle tubes, 10 x ^ in. 20 Wire gauze, 5 x 5 in. APPARATUS FOR GENERAL USE 1 doz. Asbestos sheets 2 Balances, platform, weights 500 g. to 1 g. 5 Balances, horn pan, 7 in. beam weights 100 g. to 0.01 g. 1 Barometer 5 Beakers, 1000 com. 3 Dry cells 4 Bottles, 2 liter (Acid bottles) 12 Bottles, ground glass stoppers, 1 liter 100 Bottles, ground glass stoppers, 250 ccin. 50 Bottles, salt mouth, 8 oz. 10 Bottles, salt mouth, 16 oz. 4 Burettes, 50 com., graduated 1 Combustion furnace ] 15 ft. Combustion tub- ^ 19 ing, 1 cm. inside diam. J ai 1 set Cork borers (6 in set) 1 gross Corks, assorted 1 Eudiometer and standard, coil and mercury (10 Ib.) Exp. 33 2 Dishes, evaporating, 6 in. 1 Dish, evaporating, 10 in. 2 Files, round 6 Flasks, flat bottom, 1000 com., 1- and 2-hole rubber stopper to fit 4 Funnels, glass, 4 in. 1 Funnel, glass, 6 in. 3 Gas measuring tubes, graduated, 12 in. long, | in. inside diameter 4 Gas measuring tubes, not gradu- ated, 12 in. long, in. inside diameter 1 Gas pipe, iron, 20 x in. 2 Graduates, 1000 com. 2 Graduates, 500 com. 4 Graduates, 100 com. 1 Hammer 3 Lamp chimneys (student) 2 Magnets 2 Magnifying glasses 1 Mortar and pestle, iron, 6 in. 2 Pinch cocks, Mohr's, medium 2 Pipettes, 100 com. 2 Pipettes, 20 ccm. 6 Plates, porcelain, 6 in. (Buy in crockery store) Platinum foil, T ^ 57 in., 2 sq. in. Platinum wire, No. 27, 25 in. 2 Ib. Rubber stoppers, 1 and 2 hole, Nos. 0-5 2 Separating funnels, 100 ccm. 2 Thermometers, 0-200 NOTE ON APPARATUS AND CHEMICALS 143 NOTE ON PURCHASING APPARATUS AND CHEMICALS The preceding lists of apparatus and chemicals include everything needed for a class of ten students working individually and performing all the experiments, and for all the instructor's experiments, in a school where chemistry has never been taught before. For the second and all subsequent years, the lists may be greatly cut down. The quantities of chemicals specified will last, in many instances, several years. It is not economical to buy in smaller quantities, however, because the prices charged are proportionately much higher. With careful handling, much of the apparatus for general use need never be replaced. The attention of instructors in schools handicapped by lack of funds is called to the following suggestions for minimizing the expense for chemi- cals and apparatus. When unusual or expensive apparatus is called for in the Manual, suggestions for substituting other materials are frequently made (see p. x, xi, xii, 13, 16, 21, 26, 28, 32, 40, 69). The barometer, thermometers, dry cells, induction coil and mercury may be borrowed generally from the physics department (possibly the eudiometer, also). Test-tube racks may be constructed in the manual training department. Lead dishes may be made out of sheet lead ; blowpipes from glass tubing (see p. 91). For satisfactory results, Exp. 47 requires a combustion furnace, useful also in Exp. 16 a. By omitting Exp. 47 and (if the apparatus cannot be borrowed or devised from available material) Exps. 16 a and 33, a rela- tively great saving can be effected. Condensers and clamps to hold them are relatively expensive and are used only in Exps. 21 and 61. By hav- ing students use this apparatus in turn, the number may be cut down to three if necessary (or entirely eliminated, see p. 40) . Similarly, six re- torts may be made to serve for Exp. 36. Though it is not recommended, students may work in pairs. Much of the apparatus listed for general use is for the instructor's use and convenience about the laboratory. It is possible, however, to get along with one half of the bottles, evaporating dishes, funnels, gas measuring tubes and graduates mentioned in this list. If all the above devices are adopted, a saving of from one half to one third of the cost of the lists as printed may be accomplished. This apparent saving will be at the expense of the instructor, from whom addi- tional labor will be necessitated. It is to be regarded as doubtful econ- omy, for the efficiency of his teaching is likely to be lessened thereby. Printed in the United States of America. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. MAY 3 1933 193 MAY 5 ocr LD 21-50m-l,'33 re 667 381717 UNIVERSITY OF CALIFORNIA LIBRARY