LABOMTORY PRACTICE N CHEMISTRY UC-NRLF SB 3Db 552 GIFT OF Publisher EDUCATION DEPT. From the collection of the n Prelinger a JJibrary p San Francisco, California 2006 Funnel Mortar and pestle Pipe stem triangle Forceps Deflagrat ing Funnel tube Blowpipe Florence flask Evaporating dish Beaker Porcelain crucible and cover Wa CaCO 3 + H 2 O The calcium carbonate so formed is a white solid and is in- soluble in water, and hence separates, as fast as formed, thus causing the limewater to become cloudy. This reaction serves as a good test for carbon dioxide. 2. Arrange an apparatus as shown in Fig. 52. Place in the glass tube A 5 or 6 small pieces of charcoal and connect the apparatus as shown. Pour about 10 cc. of clear limewater into the bottle C. Now turn the water cock slightly so that a slow current of water flows into the bottle B. This forces the air in the bottle out and over the charcoal in A and finally up through the limewater in C. Continue for one or two minutes, (a) Is there any change in the appearance of the limewater? Turn off the water and gradually heat the charcoal in tube A with the wing-top burner. When the charcoal is hot continue the heating and again turn on the water so that a slow current of [46] air is forced over the hot charcoal, (b) Note again any change in the limewater. (c) Is carbon dioxide formed in the experi- ment? (d) What is its source? (e) Write the equation for its Water pipe Charcoal Air Limewater FIG. 52. The formation of carbon dioxide by the direct combination of carbon and oxygen formation. (The percentage of carbon dioxide in the air is so small that it has no appreciable effect on the limewater during the time of the experiment.) EXERCISE 23 A STUDY OF CARBON DIOXIDE Apparatus. Hydrogen generator with connections, as shown in Fig. 53 ; three 25o-cc. bottles ; small beaker or test tube ; hard-giass test tube ; glass rod. Materials. 5 pieces of marble (size of walnuts); hydrochloric acid; splints; limewater (R.S.); 3 g. of copper oxide and an equal bulk of powdered charcoal. 1. Usual laboratory method for preparing carbon dioxide. Place some pieces of marble in your hydrogen generator and [47] connect as shown in Fig. 53. Add water through the funnel tube until the marble is covered with the liquid ; then add hydro- chloric acid, a few drops at a time. Carbon dioxide is formed, passes out through the exit tube, and collects in the bottle B. Collect three bottles of the gas by displacement of air. To test when filled, hold a burning splint at the mouth of the bottle ; the gas will extinguish the flame. (a) Why not collect the gas over water as in the case of oxygen and hydrogen? 2. Properties of carbon di- oxide, (b) Note the color and odor of the gas. (c) Pour the gas in one of the bottles into another bottle filled with air, just as you would pour water; then test for the gas in each of the bottles with a lighted splint. (d) What do the results show in reference to the density of the gas as compared with air? 3. Chemical conduct of carbon dioxide. Introduce a lighted splint into a bottle of the gas. (e) Is the gas combustible? (/) Is it a supporter of combustion ? o M 7T FIG. 53. The preparation of carbon dioxide by the action of hydrochloric acid on marble FIG. 54. Testing for carbon dioxide, using a drop of limewater Pour 5 cc. of clear limewater into one of the bottles; then close the bottle with your hand and shake the liquid, (g) Ex- plain the results. [48] (h) Mix together in a mortar 2 or 3 g. of black copper oxide and an equal bulk of powdered charcoal. Transfer to a hard- glass test tube and heat gently. The copper oxide is reduced to copper, the oxygen combining with the hot carbon to form carbon dioxide. Prove the presence of carbon dioxide in the tube as follows : Dip the end of a glass rod into limewater and withdraw it gently so that a drop of the clear liquid remains clinging to the end of the rod. Lower this carefully into the tube (Fig. 54). Any carbon dioxide present will cause the drop of liquid to become cloudy, (i) What kind of an agent is carbon? (;) Briefly summarize the properties and chemical conduct of carbon dioxide. EXERCISE 24 THE PREPARATION AND PROPERTIES OF CARBON MONOXIDE (OPTIONAL) Apparatus. The apparatus shown in Fig. 55 : A is a funnel, con- nected by a rubber tube with a piece of glass tubing which passes through a stopper into the 25o-cc. flask B\ C is a small clamp; pneu- matic trough ; 3 wide-mouthed bottles ; 3 glass plates 10 cm. square. Materials. Sulfuric acid; 25 cc. formic acid (50 per cent); lime- water (R. S.). Precaution. Carbon monoxide is a nearly odorless and very poisonous gas and must not be breathed. All the experiments must be performed in the hood. After the gas is generated, pour the contents of the generator flask into a sink or jar in the hood. If a good hood is not available, the exercise should be omitted. 1. Preparation of carbon monoxide. Remove the stopper from the flask B (Fig. 55), pour in 15 cc. of sulfuric acid, and connect the apparatus as shown in the figure. Close the clamp C and partially fill the funnel A with the formic acid. Now open the clamp carefully so that the formic acid will enter the flask drop by drop. Allow 8 or 10 drops to flow in ; then close the clamp. If the reaction does not begin (as indicated by [49] -Formic acid FIG. 55. Preparing carbon monoxide by the action of sulfuric acid on formic acid absence of effervescence of the liquid in the flask and escape of gas through the exit tube), heat the flask very gently until the reaction starts; then open the clamp again and admit the formic acid, a drop at a time, so as to secure a regular flow of gas from the flask. If necessary, add more for- mic acid to the funnel so as to keep it partially filled. Collect three bot- tles of the gas as shown in the figure, being care- ful to note which of the bottles was the first one filled. Close the clamp so as to stop further gen- eration of gas. Slip the glass plates over the mouths of the bottles and remove the bottles from the trough, keeping them closed with the glass plates, (a) Write the equation for the preparation of the oxide from formic acid. 2. Properties and chemical conduct of carbon monoxide. (b) Has the gas any color? (c) Is it soluble in water? (d) In the first bottle filled under i is the gas pure carbon monoxide? Test it by introducing a burning splint into the bottle ; then repeat with the second bottle, (e) Is the gas com- bustible? (/) Is it a supporter of combustion? Slip the glass plate from the third bottle just far enough to pour into the bottle 5 cc. of clear limewater ; then quickly replace the glass plate and, holding it firmly against the mouth of the bottle, shake the contents of the bottle. Note any change in the ap- pearance of the limewater. Now tip the bottle as far as possible without spilling the limewater; remove the glass plate and quickly ignite the gas, holding the bottle in this position so that at least a portion of the combustion product may be retained in [50] the bottle. When the flame dies out, at once cover the mouth of the bottle with the glass plate and shake the contents. (g) Record and explain the results. 3. (h) Summarize the properties and chemical conduct of carbon monoxide. EXERCISE 25 THE DETERMINATION OF THE RELATIVE VOLUMES OF OXYGEN AND NITROGEN IN THE AIR (OPTIONAL) Apparatus. Apparatus shown in Fig. 56. This is the same as shown in Fig. 43, Exercise 16, except that bottle B holds not less than 2 1. while bottle C holds about il.; pneumatic trough; wing-top burner; cork to fit bottle C ; graduated cylinder. Materials. Copper gauze spiral used in Exercise 16. If the spiral is oxidized, reduce it as directed in 3, Exercise 16. 1. To determine the relative volume of oxygen and nitrogen in air, a definite volume of air is passed slowly over hot copper, FIG. 56. Determining the relative volumes of oxygen and nitrogen in the air which combines with the oxygen. The remaining nitrogen is collected and its volume measured. The experiment is the same as in Exercise 16 except that the volume of the air used and that of the resulting nitrogen are both measured, [51] Arrange the apparatus as shown in Fig. 56. The glass tube A contains the copper spiral. This spiral must be of such a size that it will just enter the tube and yet can be easily pushed to the middle part of the tube in the position shown in the figure. See that the corks and tubes are air-tight. At the be- ginning of the experiment bottle B is empty, while bottle C is completely filled with water and inverted in G. The end of tube D must touch the bottom of bottle B. When the apparatus is all connected, heat the copper spiral in tube A with a wing-top burner until it is a dull-red heat, and proceed to prepare nitrogen exactly as in i, Exercise 16. Care must be taken not to hasten the experiment, as some of the oxygen may not combine with the copper. When the bottle C is nearly filled, turn off the water, withdraw the heat, and disconnect the apparatus. Now raise (or lower) the bottle C until the level of the water inside and outside the bottle is the same (it may be necessary to add more water to the trough) ; then, while holding it in this position, push the cork tightly into the mouth of the bottle. The bottle is then quickly raised from the trough and placed in an upright position on your desk. By means of a graduated cylinder measure the volume of the water in B ; this equals the volume of air analyzed. Record the volume in the table below. In the same way measure the volume of the nitrogen in C (this contains about i per cent of rare gases, chiefly argon) and record it in the table. Then from your results calculate the volumes of nitrogen and oxygen in 100 volumes of air, recalling that 100 volumes of air contains approximately i volume of the rare gases which remain mixed with the nitrogen. Volume of air analyzed (volume of water in B} . cc. Volume of nitrogen and rare gases in the volume of air analyzed (volume of gas in C) cc. Volume of oxygen in air analyzed (difference be- tween the two volumes above) cc. [521 Volume of nitrogen and rare gases in 100 volumes of air (calculate) cc. Volume of nitrogen alone in 100 volumes of air (equals volume of nitrogen and rare gases in 100 volumes of air less i volume) cc. Volume of oxygen in 100 volumes of air (calculate) cc. AVERAGE OF RESULTS RESULTS OBTAINED 4 ACTUAL OBTAINED BY CLASS Volumes of oxygen in 100 volumes of air 21 Volumes of nitrogen in 100 volumes of air 78 2. (a) What are the sources of error in the above experi- ment? (b) Why is no attention paid to the temperature of the gases or to the barometric pressure ? EXERCISE 26 A STUDY OF SOLUTIONS Apparatus. Test tubes ; graduated tube or pipette ; funnel and filter paper; loo-cc. beaker; watch glass; apparatus shown in Fig. 57 (A is a 250-cc. flask, B is a thermometer, and C is an open glass tube). Materials. 2 crystals of potassium permanganate ; 0.2 g. powdered calcium sulfate ; 3 g. common salt ; 3 g. potassium nitrate ; i g. sugar ; 10 cc. carbon tetrachloride (R. S.) ; i cc. oil (cottonseed or olive) ; log. sodium thiosulfate ; sufficient cotton to stopper a test tube. 1. Nearly fill two test tubes with water and set them in a rack. Drop into each a small crystal of potassium permanga- nate. Shake the contents of one tube and repeat the shaking after a few minutes, but do not move the other tube, (a) At the close of the laboratory period note the appearance of the liquid in each tube, (b) What do the results show? 2. Place exactly 3 g. of common salt in one test tube and an equal weight of potassium nitrate in another. Add to each exactly i cc. of water and heat each tube until the water boils. If the solid does not dissolve, add an additional cubic centi- meter of water and again heat. Repeat until the solid in each [53] tube is dissolved, avoiding any excess of water, (c) Compare the approximate solubilities of the two solids in the boiling water. (d) Cool the solutions in each tube and note the approxi- mate amounts of solids separating, (e) Compare the results with the table of solubility of solids given in the Appendix of text. 3. Introduce about 0.5 g. of sugar into each of two test tubes. To the one tube add 5 cc. of water and to the other 5 cc. of carbon tetrachloride. (/) Shake the tubes gently and note the results. Repeat the ex- periment, substituting 3 or 4 drops of an oil for the sugar, (g) How could you remove from cloth a stain due to a sugar sirup (molasses) ? to oils or grease? to a mixture of the two? 4. Introduce into a test tube 10 g. of so- dium thiosulfate (ordinary "hypo" of the photographer) and add 2 cc. of water. Heat the tube gently until a uniform solution is obtained, care being taken that no particles of the solid remain on the side of the tube ; stopper the tube loosely with a plug of cot- ton and set it aside until the solution is cold. FIG. 57. Determining If sufficient care has been taken, no solid ^ a ^^ J will have separated. Now remove the cotton plug and drop into the solution a bit of the solid "hypo" as large as a pin point, (h) Note the results (hold the tube in a good light) and explain. 5. By means of the apparatus shown in Fig. 57, determine the boiling point of a saturated solution of common salt in water, keeping the bulb of the thermometer immersed in the solution, (i) Compare the boiling point of the solution with that of pure water. [54] EXERCISE 27 S" If THE DETERMINATION OF THE SOLUBILITY OF COMMON SALT Apparatus. 6o-cc. bottle ; evaporating-dish with watch-glass cover ; beaker, tripod, and burner as shown in Fig. 58 ; funnel and filter paper ; thermometer. Materials. 15 g. common salt. 1. Introduce about 15 g. of finely powdered common salt into a 6o-cc. bottle and add 40 cc. of water. Shake the mixture vigorously and set aside for about ten minutes, repeating the shaking several times at intervals of from one to two minutes so as to form a saturated solution. Take the tem- perature of the solution and record it in the table below. Accurately weigh to o.oi g. a small evaporating-dish and watch- glass cover and record the weights in the table; then filter into the dish about 20 cc. of the saturated solution of salt and reweigh, record- ing the weights in the table. Remove the watch glass and place the dish in a beaker partially filled with water as shown in Fig 58. Keep the water in the beaker boiling. After the solution in the dish has evaporated to dry- ness, remove the dish and place it on a ring stand (Fig. 24). Now cover the dish with the watch glass and heat it directly with the burner, regulating the flame so that the tip barely touches the dish. Continue the heating until all the moisture has been expelled and the under part of the watch glass is free from moisture, (a) Why use the watch-glass cover? [55] FIG. 58. Determining the solu- bility of common salt Now withdraw the burner, and after the dish is cool (room temperature) weigh the dish, residue, and cover, recording the weights in the table. From the results so recorded, fill in the remaining "blanks in the table and make the calculations called for. (b) Compare your results with those given in the Appendix of the text. Temperature of the salt solution / Weight of empty dish and glass cover g. Weight of dish, salt solution, and glass cover .... g. Weight of salt solution taken g. Weight of dish, residue (salt) left after evaporation of water, and glass cover g. Weight of water present in solution (loss on evaporation) g. Weight of salt dissolved in the water (residue) ..... g. Weight of salt that will dissolve in 100 g. of water at the temperature of the salt solution (calculate) .... g. EXERCISE 28 THE PREPARATION AND PROPERTIES OF CHLORINE Apparatus. Test tube ; apparatus as shown in Fig. 59 (A is a 250-00. flask and B and C are 25o-cc. bottles; B contains some sulfuric acid); three additional 25o-cc. bottles (dry) ; glass plates. Materials. 25 g. manganese dioxide ; hydrochloric acid ; sulfuric acid ; bit of powdered antimony ; strips of colored calico ; piece of printed paper (printer's ink) ; paper written over with ordinary ink. Precaution. All the following experiments must be performed in the hood, and great care must be taken not to inhale the chlorine. 1. Usual laboratory method of preparation. (Two students may work together.) Arrange an apparatus according to Fig. 59. Put into the flask from 20 to 2$g. of manganese dioxide. Insert the cork and pour 150 cc. of hydrochloric acid through the funnel tube. Shake the flask so as to mix the con- tents thoroughly. Warm gently, applying just enough heat to cause a gentle evolution of the gas, but not sufficient to boil [56] the liquid. Chlorine is set free and, escaping through F, bubbles through the sulfuric acid in B (which removes all moisture) and is collected in C. Fill three bottles with the gas (tell when filled by the yellowish color of the gas, which is best seen by placing a white cardboard back of the bottle). Cover the bottles with glass plates and set them aside. Last of all, prepare some chlorine water by bringing the exit tube into a bottle contain- ing 50 cc. of water so that the gas bubbles up through the liquid. Continue the gentle heating until no more chlorine is absorbed; then cork the bottle, label it, and set it aside in a dark place ((a) c H"- j Mr n ) n 7 I B c FIG. 59. The preparation of chlorine by the ac- tion of hydrochloric acid on manganese dioxide why dark?) for future use. (b) Write the equation for the reaction that takes place in the preparation of chlorine. 2. Chemical conduct of chlorine. Grind a fragment of anti- mony to a fine powder and sprinkle a pinch of the powder into one of the bottles of the gas. SbCl 3 is formed, (c) Note the results and write the equation for the reaction. Suspend strips of colored calico in a bottle of the gas ; also two strips of paper, the one with writing in ink on it, the other with printing (printer's ink) on it. Dip similar strips of calico and paper into water until wet ; then suspend these in another bottle of the gas. (d) Record your results in each case, (e) What part does the water play in the bleaching ? 3. (/) Summarize the properties and chemical conduct of chlorine. [57] EXERCISE 29 THE PREPARATION AND PROPERTIES OF HYDROGEN CHLORIDE AND OF HYDROCHLORIC ACID Apparatus. Flask and bottle connected as shown in Fig. 60 (this is same as shown in Fig. 59, except that the bottle B contains water and the glass tube extending into the bottle B does not touch the water in B) : two 250-cc. bottles (dry) ; large beaker ; medicine dropper. Materials. Dilute sulfuric acid prepared (care) by slowly pouring (i or 2 cc. at a time with constant stirring) 30 cc. of the concentrated acid into 10 cc. water ; 50 g. sodium chloride ; splint ; blue litmus paper. 1. Usual laboratory method of preparing hydrogen chloride. (Hood.) Arrange the apparatus as shown in Fig. 60. The bottle B contains water. Care must be taken that the glass tube in the bottle B does not quite touch the surface of the water in the bottle. Put about 50 g. of common salt into the flask A, insert the cork, pour the cold dilute sulfuric acid through the funnel tube, and mix the contents by a gentle motion of the flask; then con- nect the flask with F as shown in the figure. After two or three minutes warm gently with a small flame. Notice the currents in the water in B. (a) What causes them ? When the gas is evolved regularly, disconnect the generator flask at D long enough to collect two bottles (dry) of the gas by displacement of air as in Fig. 53 (tell when filled by the fog formed at mouth of bottle). Cover these tightly with dry glass plates and set them aside ; then connect the generator [58] FIG. 60. The preparation of hydro- gen chloride by the action of sul- furic acid on sodium chloride with B again and continue to apply a gentle heat as long as any gas is evolved, (b) Write the equation for the reaction. 2. Properties and chemical conduct of hydrogen chloride. (c) What is the color of the gas (examine that in flask A}? Test the gas in one of the bottles with a lighted splint, (d) Is it combustible? (e) Is it a supporter of combustion? Fill a large beaker with water. Now uncover the remaining bottle, invert it, and at once bring its mouth under the surface of the water in the beaker and hold it in this position for two or three minutes. (/) Describe the results, (g) What does the experi- ment prove? (h) Why not extend the tube in bottle B (Fig. 60) to the bottom of the bottle ? 3. Properties of hydrochloric acid. Put a drop of the solu- tion from bottle B on a bit of blue litmus paper, (i) Note the result. (;) Pour 2 drops of the solution into 5 cc. of water and taste a drop, (k) Perform a test-tube experiment to prove the presence of chlorine in the acid ; (/) also one to prove the pres- ence of hydrogen, (m) How does the solution compare with the hydrochloric acid on your desk? 4. ( n ) State clearly the difference between the terms hydrogen chloride and hydrochloric acid. EXERCISE 30 SODIUM ; SODIUM HYDROXIDE Apparatus. Evaporating-dish with glass-plate cover ; forceps ; glass rod. Materials. Bit of sodium as large as a pea ; red litmus paper. 1. Properties of sodium. Recall experiment i, Exercise 9. Obtain from your instructor a bit of sodium. Hold the sodium with the forceps on a glass plate, cut it, and note the rapidity with which the freshly cut surface is tarnished. Half fill your evaporating-dish with water; then drop into this a bit of sodium as large as a pea, quickly cover the dish with the glass plate, and leave it covered until the sodium has all disappeared. [591 (a) Is sodium heavier or lighter than water? (b) Write the equation for the reaction between sodium and water, (c) What is the composition of the liquid in the evaporating-dish ? 2. Properties of sodium hydroxide. Place a drop of the liquid in the evaporating-dish on a piece of red litmus paper. (d) Contrast its action with that of hydrochloric acid on litmus paper (Exercise 29). Mix i or 2 drops of the solution with 5 cc. of water and taste a drop of the resulting solution. (e) Contrast with the taste of hydrochloric acid (Exercise 29). Evaporate the solution to dryness. (/) What is the residue? EXERCISE 31 THE PROPERTIES OF ACIDS, BASES, AND SALTS Apparatus. Small beaker ; stirring-rod ; evaporating-dish ; ring stand ; test tubes ; medicine dropper. Materials. A few drops of each of the following acids: hydrochloric, sulfuric, nitric, acetic ; solutions of the following bases : sodium hydrox- ide, potassium hydroxide (R. S.), calcium hydroxide (R. S.); strips of blue and of red litmus paper ; hydrochloric acid. 1. Acids. Recall the properties of hydrochloric acid (Exer- cise 29). Prepare a dilute solution of each of the following acids by adding 2 or 3 drops of the acid to about 10 cc. of water in a test tube and mixing thoroughly: hydrochloric, sulfuric, nitric, acetic. By means of a clean glass rod transfer a drop of each of the dilute solutions to a piece of blue litmus paper, (a) Note the result in each case, (b) Taste one drop of the dilute solutions (rinse the mouth with water after tasting). Compare the formulas of the acids, (c) In what respect are the acids similar in composition ? 2. Bases. In a similar way try the effect on red litmus paper of a solution of each of the following bases : sodium hydroxide (recall Exercise 30), potassium hydroxide, calcium hydroxide. (d) Do they affect the blue litmus paper? (e) Taste a drop of the calcium hydroxide solution. [60] Compare the formulas of the bases. (/) In what respect are the bases similar in composition? 3. Salts. Dilute 5 cc. of the ordinary laboratory solution of sodium hydroxide (i part of the hydroxide by weight to 10 parts of water) with an equal volume of water. To this solu- tion add 4 or 5 drops of the ordinary concentrated hydrochloric acid. Stir the resulting solution with a glass rod and test its action on blue and on red litmus paper, (g) Has it acid or basic properties? Now continue to add the acid drop by drop until the result- ing solution is neutral (that is, has no effect on either blue or red litmus paper) or is, at most, slightly acid, (h) Write the equation for the reaction between the hydroxide and the acid. Now pour the solution into an evaporating-dish and evaporate to dryness. (i) What compound remains? (;) Taste it. (k) What is the name given to the compounds formed by the action of acids on bases ? 4. (/) Characterize acids and bases as to composition; as to their action on litmus ; as to taste ; as to their interaction with each other. EXERCISE 32 THE RATIO OF ACID TO BASE IN NEUTRALIZATION Apparatus. 2 burettes and supports, as shown in Fig. 61; 2 small beakers and stirring-rod; graduated pipette. Materials. Sodium hydroxide solution prepared by adding 20 cc. of the laboratory reagent to 100 cc. water; i cc. sulfuric acid (use gradu- ated pipette) added to 100 cc. water and mixed thoroughly; a few drops of a phenolphthalein solution (R. S.). (Two students may work together.) 1. Rinse out a burette, first with distilled water and then with a little of the solution of sodium hydroxide. Support the burette (Fig. 61) and pour into it the hydroxide solution until the level of the liquid is i or 2 cm. above the zero mark. Turn the stopcock and let the solution slowly flow out until the bot- [61] torn of the" curved surface (Fig. 3) of the liquid in the burette is on a level with the zero mark. In a similar way fill a second burette with the acid solution. Now let exactly 1 5 cc. of the acid solution flow into a small beaker, add two drops of phenolphthalein solution, and run in 2 or 3 cc. of the hydroxide solution. Notice that where the liquids come in contact a reddish color is pro- duced, which disappears quickly on stirring. Run in more of the solution, a little at a time, until the color fades slowly, and then a drop at a time until the entire liquid, on stirring, remains colored faintly pink. This marks ap- proximately the point of neutralization. Record the number of cubic centimeters of the hydroxide solution used in the table below. Repeat the experiment, FIG. 61. Graduated tubes (burettes) for measuring volumes of liquids using 30 cc. of the acid, and again record in the table the number of cubic centimeters of the hydroxide solution used to neutralize the acid. First Experiment Volume of hydroxide solution used to neutralize 15 cc. of the acid cc. Volume of hydroxide solution required to neutralize i cc. of acid (calculated) Second Experiment Volume of hydroxide solution used to neutralize 30 cc. of the acid Volume of hydroxide solution required to neutralize i cc. of acid (calculated) 2. (a) What do the results of the experiments prove ? cc. cc. cc. 62] EXERCISE 33 CARBONIC ACID AND ITS SALTS (CARBONATES) Apparatus. Hydrogen generator, as used for preparing carbon dioxide in Exercise 23 ; small beaker ; 5 test tubes. Materials. Pieces of marble for generating carbon dioxide; hydro- chloric acid ; blue litmus paper ; 5 cc. sodium hydroxide solution diluted with 10 cc. water ; i g. of each of the common carbonates, such as sodium carbonate, magnesium carbonate, calcium carbonate ; 25 cc. limewater (R. S.). 1. When carbon dioxide is passed into water, a portion of the gas combines with the water to form a compound known as car- bonic acid ( H 2 O + CO 2 - > H 2 CO 3 ) . This is a very weak acid and so unstable that it can be obtained only in dilute solutions. If an attempt is made to concentrate the solution by evaporat- ing the water, the acid decomposes again into water and carbon dioxide. The salts of this acid (the carbonates), on the other hand, are stable, and many of them are important and common compounds. Thus, calcium carbonate (CaCO 3 ) is the chief constituent of limestone, while sodium carbonate (Na 2 CO 3 ) is common washing soda. Generate carbon dioxide (Fig. 53) and pass the gas through 25 cc. of water, (a) Taste the liquid, (b) Is the acid formed strong enough to affect blue litmus paper? 2. Pass carbon dioxide through 5 cc. of a solution of sodium hydroxide until the gas is no longer absorbed (the carbon dioxide combines with the water present to form carbonic acid. This acid then reacts with the base, sodium hydroxide, to form a salt and water). Evaporate the solution to dryness. (c) What is the product left in the dish? (d) Write the equa- tion for its formation, (e) Could a solution of sodium hy- droxide be used in place of a solution of calcium hydroxide (limewater) in testing for carbon dioxide? [63] 3. Examine the physical properties of such carbonates as are available. (/) What ones are soluble in water (p. 304 of text) ? Test the action of hydrochloric acid or sulfuric acid on each by adding i or 2 drops of the acid to o.i g. of the carbonate in a test tube. What evidences have you that a gas is evolved? (g) Test the gas to determine whether or not it is carbon dioxide (Fig. 54). All carbonates evolve carbon dioxide when treated with hydrochloric or sulfuric acid. This reaction serves as a good test for carbonates. EXERCISE 34 A METHOD FOR DETERMINING WHETHER A GIVEN LIQUID IS A CONDUCTOR OF ELECTRICITY (OPTIONAL) Apparatus. Current from electric-lighting system ; apparatus as shown in Fig. 62. B is a plug for connecting the apparatus with any ordinary electric-lighting system. C is an ordinary incandescent lamp. A is a small bottle (60 cc.). The wires are the common insulated cop- per wires, but the insulation is removed from that portion of the wires which extend inside the bottle A. The apparatus can be purchased from supply houses, but is easily made. Materials. 5 g. common salt ; 5 g. sugar ; 5 cc. sodium hydroxide solution added to 20 cc. water ; 3 cc. sulfuric acid added to 20 cc. water ; tap or well water ; 10 cc. hydrochloric acid ; (10 cc. of a benzene solution of hydrogen chloride). 1. Obtain from your instruc- tor the apparatus shown in Fig. 62. Polish the ends (elec- trodes) of the copper wires that extend into the bottle A with emery paper until they FIG. 62. Apparatus for determining are bright and free from oxide. whether or not a lic * uid is a conduc - ....... , , tor of electricity At the beginning of each ex- periment see that the electrodes are bright and dry and that the bottle is also perfectly clean and dry. Unscrew a lamp C from a convenient socket in the laboratory, screw it loosely [641 into the socket on your apparatus, and attach the apparatus to the empty socket on the lighting system by means of the ex- tension cord and plug B. Every time a change is to be made in the cell, loosen the lamp C in the socket, and do not screw it down to make contact until all the connections of the cell have been arranged. 2. Partly fill the bottle A with dry, powdered salt, dip the electrodes into the powder, arrange the connections at the binding-posts, and screw down the lamp C. (a) Does the salt conduct the electric current? 3. (b) Repeat 2, using distilled water. 4. (c) Repeat 2, using a solution of the salt in distilled water. 5. (d) Test the conductivity of the following substances and interpret the results : dry, powdered sugar ; a solution of sugar in water; tap or well water; distilled water containing a few drops of sulfuric acid; distilled water containing a few drops of hydrochloric acid ; a solution of sodium hydroxide, (e) How do we account for the fact that solutions of some compounds conduct the electric current while others do not? 6. Secure from your instructor 10 cc. of a benzene solution (benzene is inflammable) of hydrogen chloride (easily prepared just as an aque- ous solution is prepared, as described in Exercise 29). (/) Test its con- ductivity, (g) Test its effect on blue and on red litmus paper, (h} Does it dissolve zinc ? (i) How do you account for the difference in properties between a benzene solution of hydrogen chloride and an aqueous solu- tion of the same gas ? 7. (;) Define the terms acid, base, and salt from the stand- point of the ionization theory. 65] EXERCISE 35 THE DISPLACEMENT OF METALS FROM THEIR COMPOUNDS (THE DISPLACEMENT SERIES) Apparatus. 4 test tubes; test-tube rack. Materials. 4 clean and bright strips each of zinc and copper (i cm. x 10 cm.); 0.5 g. lead nitrate dissolved in 10 cc. water; 0.5 g. copper nitrate dissolved in 10 cc. water; 0.5 g. mercuric nitrate dis- solved in 10 cc. water; 3 cc. sulfuric acid dissolved in 10 cc. water. 1. Pour into separate test tubes to a depth of 4 or 5 cm. solu- tions of the following compounds : lead nitrate, dilute sulfuric acid, copper nitrate, mer- curic nitrate. Set the tubes in a rack in the order given above and label them A, B, C, and D respectively (Fig. 63). Now place in each tube a strip of zinc. (It is con- venient to have a strong thread attached to the upper part of each strip so that the strip may easily be withdrawn from the tube. The strips should be only partly immersed in the solution.) Note any change taking place in the appearance of the zinc. After twenty minutes withdraw the strips and wipe them on a piece of white paper, (a) Note any evidence tending to show that the zinc has displaced the lead, hydrogen, copper, and mercury from their compounds. (Metals in a very finely divided form are black, as a rule.) (b) Account for any change in the color of the copper nitrate solution. [661 FIG. 63. Testing the action of different metals on solutions of salts 2. Repeat experiment i, substituting for the zinc a strip of copper, (c) Contrast the results obtained with those obtained in i. (d) How do you account for the change in the color of the solution of mercuric nitrate after the addition of the copper strip? (e) Are your results in accord with the table of the displacement series given on page 161 of text? EXERCISE 36 THE PREPARATION AND PROPERTIES OF AMMONIA Apparatus. Test tube; hard-glass test tube fitted with cork and tubing as shown in Fig. 64 ; graduated tube ; three 250-00. wide-mouthed bottles ; 2 pieces of window glass ; large beaker ; glass rod. Materials. Solution of sodium hydroxide (the ordinary desk solution will serve) ; 9 g. ammonium chloride ; 15 g. powdered calcium hydroxide (slaked or hydrated lime,Ca(OH) 2 ); strip of red litmus paper; strip of blue litmus paper ; hydrochloric acid ; splint. 1. Dissolve 0.5 g. of ammonium chloride in 3 or 4 cc. of water in a test tube and heat to boiling, (a) Note the odor. Now add 3 cc. of a solution of sodium hydroxide to the hot solution of ammonium chloride and continue the heating. (b) Again note the odor, (c) Moisten a strip of red litmus paper and hold it at the mouth of the tube but not in contact with it. (d) Dip the end of a glass rod in a concentrated solution of hydrochloric acid and hold it in the mouth of the test tube. Dense white fumes of ammonium chloride (NH 4 C1) are formed. (e) Complete the following equations: NH 4 Cl + NaOH - > NH 3 + H 2 O >- NH 4 OH 2. Usual laboratory method for preparing ammonia. This differs from the method used in i only in the fact that the less expensive calcium hydroxide (slaked lime) is substituted [67] for the sodium hydroxide. The form of apparatus used is shown in Fig. 64. The bottle B (250-00.) contains 2500. of water. The glass tube C extends through a hole in a cardboard resting on the mouth of the bottle. The end of the tube must just touch the water in the bottle. Place in the tube A a mixture of 15 g. of powdered slaked lime and 8 g. of ammonium chloride. Connect the tube as shown in Fig. 64 and heat the mixture gently, beginning with that portion near the mouth of the tube and gradu- ally extending the heat to the other portions. As soon as the gas is evolved freely (as shown by the bubbles at the end of the tube C), bring the tube C to an upright position, as FIG. 64. Preparing ammonia by heating a mix- ture of ammonium chloride and calcium hy- droxide (slaked lime) shown in the dotted lines, and collect two bottles of the gas. To do this, bring the bottles successively down over the exit tube, leave each in this position until a drop of hydrochloric acid on the end of a glass rod fumes strongly when held at the mouth of the bottle ; then withdraw the bottle, cover its mouth with a glass plate, and set it aside, mouth downward. When both bottles are filled, bring the tube C into the bottle B again and continue to heat the mixture gently as long as any gas is generated. (/) Write the equations for all the reactions involved. 3. Properties and chemical conduct of ammonia, (g) Note the color and odor of the gas. (h) Is it heavier or lighter than air? (i) Test a bottle of the gas with a burning splint. [68] Devise a simple experiment for finding out whether or not ammonia is soluble in water. After your method is approved by the instructor, try it out with the remaining bottle of the gas. (;) Describe the results. 4. Properties of ammonium hydroxide, (k) Note the odor of the liquid in the bottle B. (I) Try its effect on blue and on red litmus paper, (m) How does it compare with the aqua ammonia of the druggist in its odor and its action on litmus? (n) Does the gas combine with the water or is it simply dis- solved in the water ? (0) Give reasons for your answer. Now neutralize the liquid with hydrochloric acid and evaporate just to dry ness (Fig. 58). (/>) Compare the residue with the am- monium chloride used in experiment i. 5. (q) Summarize the properties and chemical conduct of ammonia. EXERCISE 37 THE PREPARATION AND PROPERTIES OF NITRIC ACID Apparatus. Glass retort (150-00.), test tube, and beaker (500-00.), arranged as shown in Fig. 65; funnel; evaporating-dish. Materials. 12 g. sodium nitrate ; 10 cc. sulfuric acid ; small piece of tin; small strip of copper. Caution. The students must remember that both sulfuric acid and nitric acid are very corrosive and must exercise care in handling them. 1. Preparation of nitric acid. Arrange an apparatus like that shown in Fig. 65. Put in the retort A about 12 g. of sodium nitrate and 10 cc. of sulfuric acid, pouring the latter through a funnel placed in the tubulus B of the retort. Heat the mix- ture gently with a small flame. Nitric acid is set free, distills over, and is condensed in the test tube C, which is kept cold by being partly immersed in ice water in the beaker D. (a) Write the equation for the reaction between the sulfuric acid and the sodium nitrate. [69] 2. Properties and chemical conduct of nitric acid. When nitric acid is heated, a part of it is decomposed into water, nitrogen dioxide, and oxygen. On this account it is a good oxidizing agent. To test its oxidizing properties, put a small piece of tin in a test tube, cover it with a little nitric acid, and gently heat (hood). The white product formed is composed mainly of tin and oxy- gen, the latter being supplied by the nitric acid. Pure nitric acid is colorless, (b) How do you account for the color of the acid which FIG. 65. The preparation of nitric acid by the action of sulfuric acid on sodium nitrate you have prepared? Place a small strip of copper in an evaporating-dish (hood) and add some of the acid you have prepared, a few drops at a time, until the copper is just dissolved. Evaporate the solution to dryness (Fig. 58). (c) Note the appearance of the residue, (d) Since copper is below hydrogen in the displacement series, how do you account for the fact that nitric acid dissolves the metal (consult text) ? Save the residue in the dish ((e) what is it?) for use in the following exercise. [70 EXERCISE 38 THE PROPERTIES OF THE SALTS OF NITRIC ACID (NITRATES) Apparatus. Evaporating-dish containing the copper nitrate prepared in Exercise 37 ; 5 test tubes in test-tube rack; medicine dropper. Materials. Strip of copper ; crystal of lead nitrate ; crystals of such nitrates as are available, including sodium nitrate and potassium nitrate ; sulfuric acid ; 2 g. ferrous sulfate dissolved in 10 cc. water. 1. Properties of nitrates. Heat the dish (hood) containing the copper nitrate, prepared in Exercise 37, with a small flame. (a) Note the color of the gas evolved, also the color of the residue, (b) Compare the residue with the crust of copper oxide prepared by holding a strip of copper in the tip of a flame. Place a crystal of lead nitrate in the evaporating-dish and heat gently, (c) Compare with the results obtained in i. Place a small crystal of such nitrates as are available in your laboratory in separate test tubes and test their solubility in water; (d) What nitrates are insoluble in water (consult text) ? 2. How to detect the presence of a nitrate. Dissolve a crystal of sodium nitrate in 2 or 3 cc. of water in a test tube, add drop by drop an equal volume of sulfuric acid, mixing the liquids as the acid is added, then cool the mixture. The sulfuric acid acts on the nitrate, liberating nitric acid. Now tip the tube slightly and gently pour 2 or 3 cc. of the solution of ferrous sulfate down the side of the tube, so that it floats on the heavier liquid, and set the tube aside, being careful not to mix the two liquids. A brown ring soon forms where the liquids meet. Repeat the experiment, using potassium nitrate. This is a good test for nitrates. The brown ring is due to the presence of a com- pound formed by the action of ferrous sulfate on nitric acid. Secure one or more compounds from your instructor and test to see if they are nitrates, (e) Record your results. [71] EXERCISE 39 THE PREPARATION AND PROPERTIES OF SOME OF THE OXIDES OF NITROGEN Apparatus. Hard-glass test tube, with delivery tube, as used in pre- paring oxygen (Fig. 28); 3 wide-mouthed bottles (250-00.); pneumatic trough; hydrogen generator (Fig. 35)52 glass plates. Materials. 8g. ammonium nitrate; wooden splints; 5 small strips of copper; 10 cc. nitric acid. 1. Nitrous oxide. Put 6 or 8 g. of ammonium nitrate in the hard-glass test tube used in the preparation of oxygen (Fig. 28). Attach a delivery tube and heat gently, applying no more heat than is necessary to cause a slow evolution of the gas. As soon as the gas is regularly evolved, collect two or three bottles of it over water. Notice the water deposited on the sides of the test tube, (a) What is the source of it? (b) Note the color, odor, and taste of the gas. (c) Test it with a glowing splint, (d) Account for the result, (e) How can you distin- guish between nitrous oxide and oxygen ? 2. Nitric oxide and nitrogen dioxide. Put a few pieces of copper in your hydrogen generator (hood) (Fig. 35), just cover them with water, and add 2 or 3 cc. of nitric acid. Collect over water two bottles of the evolved gas, adding more nitric acid to the liquid in the generator if necessary to secure the required amount of gas. (/) Compare the color of the gas in the generator with, that collected in the bottles and account for any difference. (g) Write the equations for all the reactions involved. (h) Uncover one of the bottles of the gas and account for the result, (i) Test the gas in the second bottle with a burning splint. (;) Which is the more stable, nitrous oxide or nitric oxide? (k) Give reasons for your answer. 72] EXERCISE 40 THE PROPERTIES AND CHEMICAL CONDUCT OF SULFUR Apparatus. 3 test tubes; smallest-sized beaker; magnifying-glass ; porcelain crucible ; pipestem triangle ; large beaker ; steel forceps. Materials. 5 cc. carbon disulfide ; 20 g. powdered brimstone ; strip of copper foil (0.5 x 3 cm.) ; 5 g. iron powder. 1. Properties of sulfur, (a) Examine the physical prop- erties of a piece of brimstone. Pour 2 or 3 cc. of carbon disul- fide (hood) over 2 g. of powdered brimstone in a test tube. (Keep carbon disulfide away from flame and do not inhale the vapor.} Cover the mouth of the tube with the thumb and shake the contents gently until the sulfur is dissolved, adding more carbon disulfide if necessary. Pour the clear solution into a small beaker, cover the beaker loosely with a filter paper, and set it aside in the hood. The carbon disulfide soon evapo- rates, the sulfur being deposited in crystals, (b) Examine these with a magnifying-glass, noting their general shape. Half fill a test tube with powdered brimstone and heat it gently until the sulfur is just melted, (c) Note the properties of. the liquid. Now apply a stronger heat and observe that the liquid becomes darker, and at a certain temperature (200- 250) is so thick that the tube may be inverted without spill- ing it. Finally, increase the heat until the sulfur boils (448), and then slowly pour the boiling liquid into a beaker of cold water, (d) Examine the product, (e) What name is given to this form of sulfur ? Expose it to the air for an hour or longer. (/) Have its properties remained unchanged? Fill a porcelain crucible with powdered brimstone and apply a very gentle heat until the sulfur is just melted. Withdraw the flame and examine the liquid carefully as it cools. Crystals soon begin to form on the surface of the melted sulfur, rapidly extending from the circumference toward the center. Before [73] they reach the center grasp the crucible with the forceps and quickly pour off the remaining liquid and examine the crystals. (g) Compare them in shape with those deposited from the solution of carbon disulfide. (h) In how many forms have you obtained sulfur? 2. Chemical conduct of sul- fur. Burn a small piece of sulfur. (/') Notice the appear- ance of the burning sulfur and the odor of the gas (SO 2 ) formed. Boil a little sulfur in a test tube and drop a small strip of hot copper foil (Fig. 66) in the boiling liquid. (;) Is there any visible evidence of FIG. 66. Dropping a piece of copper foil into boiling sulfur a chemical change? (k) What is formed ? Grind together 5 or 6 g. of iron powder with an equal weight of sulfur, transfer the mixture to a test tube, and heat it strongly in a Bunsen flame. (/) Describe the results. Retain the solid formed for use in the following exercise. 3. (m) Summarize the properties and conduct of sulfur. EXERCISE 41 THE PREPARATION AND PROPERTIES OF HYDROGEN SULFIDE Apparatus. Hydrogen generator and tubes, as shown in Fig. 67 ; 2 wide-mouthed bottles (250-00. and 6o-cc.) ; funnel ; evaporating-dish. Materials. 10 g. ferrous sulfide (in pieces as big as a bean or larger) ; 20 cc. hydrochloric acid added to 20 cc. water ; blue and red litmus papers ; silver coin ; filter paper. 1. (Hood.) Attach a delivery tube to the hydrogen gen- erator, as shown in Fig. 67. Put into the generator A a few [74] o JR TT pieces of ferrous sulfide (FeS) and insert the stopper. Now pour a little water through the funnel tube of the generator until the end of the tube just dips below the surface of the water ; then pour in a few cc. of the hydrochloric acid, adding more from time to time, if necessary, to maintain a gentle evolution of the gas. (a) Write the equation. The gas escapes into the bottle B, which gradually becomes filled, (b) Very cautiously note the odor (Caution. The gas is poisonous if inhaled in concentrated form) ; (c) also note the color of the evolved gas. Continue the evo- lution of the gas until it is ignited by a flame held at the mouth of the bottle B. (d) Ac- count for the deposit formed on the sides of the bottle when the gas burns. 2. Replace the bottle B with a 6o-cc. bottle half filled with water, and allow the gas from the generator (add more acid if necessary) to bubble through the water for one or two min- utes. Test the resulting solution with blue and with red litmus paper, (e) What is the solution called? (/) How does it compare with the so-called "sulfur water" of many springs? (g) Drop a silver coin into the solution and account for the results, (h) Why do certain foods blacken silver spoons? 3. Transfer to a test tube a piece of the solid formed in 2, Exercise 40, by heating a mixture of iron and sulfur and add i or 2 cc. of dilute hydrochloric acid, (i) What gas is evolved (cautiously note the odor) ? (j) Account for its formation. 4. (k) Summarize the properties of hydrogen sulfide. B FIG. 67. Preparing hydrogen sulfide by the action of hydrochloric acid on ferrous sulfide [75 EXERCISE 42 THE PREPARATION AND PROPERTIES OF THE SALTS OF HYDROSULFURIC ACID (SULFIDES) Apparatus. Hydrogen generator and connections, as shown in Fig. 68 ; 6 test tubes ; beaker ; funnel ; watch glass ; iron spoon. Materials. Ferrous sulfide and dilute hydrochloric acid, as used in Exercise 41 ; separate solutions of silver nitrate, copper, sulfate, cad- mium chloride, lead nitrate, and sodium chloride, made by dissolving about 0.5 g. of the solid in 5 cc. water (solutions on reagent shelf may be used) ; sulfuric acid ; lead acetate (R. S.) ; 5 g. sulfur; 3 g. lime. 1. Preparation of sulfides. (Hood.) Charge the hydrogen sulfide generator as in Exercise 41 and pass a few bubbles of the gas (Fig. 68) through each of the following solutions: silver nitrate, copper sulfate, cadmium chloride, sodium chloride, lead nitrate. The exit tube C, through which the gas bubbles into the solu- tions, must be thoroughly cleaned each time, (a) Note the color of the precipitate obtained in each case. Write the equations for the reac- tions involved, (b) Do any of the solutions fail to give a precipitate? (c) How do you O A FIG. 68. Preparing sulfides of the metals by passing hydrogen sulfide through a solution of their salts account for this ? Intimately mix 5 g. of sul- fur with 3 g. of powdered lime. Transfer to a beaker and add i5occ. of water. Stir the mixture and heat just to boiling for ten minutes. Now fill a test tube with the resulting mixture, cork the tube loosely, and set it aside until the beginning of the next laboratory period; then examine, (d) Describe the [76] results., (e) For what is the solution used (consult text) ? (/) What is its composition (consult text) ? 2. Test for hydrogen sulfide. Dip a strip of filter paper into a solution of lead acetate. Remove the cork from the hydrogen sulfide generator and insert the paper for a moment, (g) Note and account for the results. This serves as a convenient test for the gas. (h) What property would also serve to detect the gas if present in any marked quantity? 3. Test for sulfides. Prepare some dilute sulfuric acid by adding (care) 2 or 3 drops of the acid on your desk to i cc. of water. Place a small bit of ferrous sulfide (FeS) on your watch glass and moisten it with the dilute acid. Cautiously note the odor. Most of the sulfides when treated in this way evolve hydrogen sulfide, which can be detected by its odor and by its action on paper moistened with lead acetate solution. All sulfides when heated in air evolve sulfur dioxide (formed by the combustion of the sulfur present), which has the char- acteristic odor of burning sulfur, (i) Heat a little ferrous sul- fide on an iron spoon in the flame of the burner and note the odor. EXERCISE 43 SULFUR DIOXIDE AND SULFUROUS ACID Apparatus. 25o-cc. flask fitted with funnel tube and glass exit tube, as shown in Fig. 69 ; 3 bottles (250-00.) ; watch glass ; medicine dropper. Materials. 10 g. copper ; sulfuric acid ; splint ; blue litmus paper ; crystal of sodium sulfite ; strips of colored calico or a red flower. 1. (a) By what method have you already prepared sulfur dioxide ? 2. Preparation of sulfur dioxide and sulfurous acid by the action of sulfuric acid on copper (laboratory method). Place about 10 g. of copper turnings or small pieces of sheet copper in a generator arranged as in Fig. 69. Add 250:. of concen- [77] trated sulfuric acid and apply a gentle heat. As soon, as the action begins, lower the flame, regulating it so as to obtain a uniform evolution of the gas. Collect two bottles of the gas by displacement of air; then cause it to bubble through 2 5 cc. of water as long as any is dissolved, (b) Write the equation for the reaction of sulfuric acid on copper. 3. Properties and chemical conduct of sulfur dioxide and sulfurous acid, (c) Note the odor of the gas. (d) Is the gas combustible? (e) Test with blue litmus paper the liquid formed by passing the gas FIG. 69. Preparing sulfur dioxide by the action of sulfuric acid on copper through water. (/) Does the gas combine with the water or simply dissolve in it ? (g) Give reasons for your answer, (h) Immerse in the liquid some small strips of colored calico or some petals of a red flower and note any results. 4. Salts of sulfurous acid; the sulfites. Place a small crystal of some sulfite, such as sodium sulfite (Na 2 SO 3 ), on a watch glass and moisten it with 2 or 3 drops of sulfuric acid, (i) Note the odor of the evolved gas. All sulfites evolve sulfur dioxide when treated with sulfuric acid. This reaction serves as a good test for sulfites. It also serves as a method for preparing sulfur dioxide. 5. (j) Enumerate three methods for preparing sulfur dioxide. 6. (k) Briefly summarize the properties and chemical con- duct of sulfur dioxide. [78] EXERCISE 44 A STUDY OF SULFURIC ACID Apparatus. Stirring-rod ; test tubes ; medicine dropper. Materials. Sulfuric acid ; 0.5 g. sugar ; wooden splint ; a small piece of zinc; piece of charcoal the size of a pea; barium chloride solution (R.S.); hydrochloric acid. 1. Properties and chemical conduct of sulfuric acid. By means of a glass rod place i or 2 drops of sulfuric acid on a wooden splint, and after two or three minutes (a) note the results produced. Put about 0.5 g. of sugar in a test tube and add 3 or 4 drops of the acid, (b) Note and account for the change produced. Heat a bit of charcoal in a test tube with i or 2 cc. of con- centrated sulfuric acid, (c) What gas is evolved (odor) ? (d) Account for its formation, recalling that carbon has a strong affinity for oxygen. In the preparation of hydrogen (Exercise 9) the directions called for dilute sulfuric acid, (e) Determine whether the concentrated acid will do as well, by pouring 2 or 3 cc. of the acid over a bit of zinc in a test tube (if no action takes place, heat the mixture gently and test the gas evolved both by a lighted splint and by noting its odor). (/) Account for the difference in the action on zinc between the dilute and the concentrated acid. Recall the action of sulfuric acid on sodium chloride (Exer- cise 29) and on sodium nitrate (Exercise 37). (g) What prop- erty of sulfuric acid enables it to be used in the preparation of other acids ? 2. Test for sulfuric acid. Add 3 drops of sulfuric acid (care) to 5 cc. of water in a test tube. To this add a few drops of a solution of barium chloride. The chloride reacts with the acid to form barium sulfate (BaSO 4 ), which is insoluble and hence [79] separates, as fast as formed, as a white precipitate, (h) Write the equation for the formation of the barium sulfate. Now add to the precipitate 4 or 5 drops of hydrochloric acid, (i) Does the precipitate dissolve ? The formation of a white precipitate with barium chloride, insoluble in hydrochloric acid, consti- tutes a good test for sulfuric acid. EXERCISE 45 SALTS OF SULFURIC ACID (SULFATES) Apparatus. 6 test tubes. Materials. Crystals or small amounts (o.i g.) of the sulfates avail- able in the laboratory; 2 cc. barium chloride solution (R.S.); hydro- chloric acid. 1. Examine the physical properties of such sulfates as are available. Test the solubility of each in water by adding about 0.5 g. of the sulfate to a test tube nearly filled with water and shaking the mixture, (a) What sulfates are insoluble (consult text) ? 2. Prepare a dilute solution of different sulfates by dissolv- ing a crystal of each in 2 or 3 cc. of water. Add to each i drop of barium chloride solution. Now add 2 drops of hydrochloric acid to the mixture in each tube, (b) Does the precipitate dis- solve? All soluble sulfates give in solution a white precipitate (BaSO 4 ) with barium chloride solution, which precipitate is insoluble in hydrochloric acid. This reaction serves as a good test for sulfates. It will be noted that both sulfuric acid and its salts give with barium chloride the same product; namely, a white precipitate of barium sul- fate. This is evident from the following facts : It will be recalled that both acids and salts are ionized in solution. In the case of sulfuric acid and sulfates, ions are formed as follows : H 2 S0 4 >-H+ H+ + S0 4 Na~S0 4 >-Na+, Na+-f SO, CuS0 4 > Cu+ + + S0 4 [801 Likewise, barium chloride solution contains the ions Ba++ and Cl~, Cl~. Now when a solution of barium chloride is mixed with any so- lution containing the SO 4 ion, the two ions Ba++ and S0 4 unite to form the insoluble BaSO 4 , which precipitates; hence the reaction proceeds to completion (paragraph 2, p. 179 of text). The barium chloride test is therefore really a test for the presence of the SO 4 ion. Since only sulfuric acid and its salts give this ion, however, it is cus- tomary to say that it is a test for sulfuric acid and the sulfates. EXERCISE 46 THE PREPARATION AND PROPERTIES OF HYDROGEN FLUORIDE Apparatus. Piece of window glass; small lead dish (laboratory outfit). Materials. 2 or 3 small pieces of paraffin (size of a pea) ; 3 g. fluor- ite (CaF 2 ) ; sulfuric acid. Precaution. Hydrogen fluoride is very corrosive and must not be inhaled ; neither must its solution be brought in contact with the skin. 1. Place some pieces of paraffin on a glass plate and gently warm the plate over a small flame. When the paraffin is melted, tilt the plate about so as to form a uniform layer of the wax. When the wax is cold, scratch your name through the wax with a pin (Fig. 70). Place 3 g. of fluorite in a lead dish and add suffi- FlG . 70 . Preparing a glass plate for etching cient sulfuric acid to make a paste of it. Cover the dish tightly with the waxed side of the glass plate and set it in the hood for an hour ; then scrape off the paraffin and examine the glass, (a) Describe the-results. (b) Write the equations for all the reactions involved. [81 EXERCISE 47 THE PREPARATION AND PROPERTIES OF BROMINE Apparatus. Retort, test tube, and beaker, as shown in Fig. 71 ; funnel. Materials. 3 g. sodium bromide or potassium bromide ; 4 g. manga- nese dioxide ; 10 cc. sulfuric acid dissolved in 40 cc. water ; strips of col- ored calico; i cc. carbon tetrachloride ; i cc. of chlorine water (R. S.). Precaution. The vapor of bromine must not be inhaled. 1. Preparation of bromine. Put into the retort (A, Fig. 71) a mixture of 2 g. of potassium bromide or of sodium bromide and 4 g. of manganese dioxide, and add to this through a funnel the cold dilute solution of sulfuric acid prepared as directed above. Shake the re- tort so as to mix the contents thoroughly. Note that the test- tube receiver C con- tains sufficient water to allow the end of the retort to dip just below its surface. Now heat the retort gently. The bromine is liberated and dis- JM1 / \ TIT , tills over, (a) Write FIG. 71. Preparing bromine by the action of Sul- * ur * c ac ^ on a Imxture f manganese dioxide and sodium bromide the equation for the reaction. Continue the heating until all the bromine has distilled over. Remove the stopper from the retort before the heat is withdrawn. 2. Properties of bromine, (b) Note the properties of the bromine collected in the bottom of the test tube, (c) Has any dissolved in the water (note the color of the water) ? (d) What property is implied in the name of the element? Add about 0.5 cc. of the aqueous bromine solution to i cc. of carbon [82] tetrachloride. Note that the bromine solution does not mix with the carbon tetrachloride but floats on top of it. Now place your thumb over the mouth of the tube and shake the mixture vigorously for a few seconds ; then set the tube aside until the two liquids separate. The bromine, being more soluble in carbon tetrachloride than in water, is taken up by the former liquid. (e) What is the color of the carbon tetrachloride solution? Test the bleaching property of bromine by immersing strips of colored cloth in the aqueous solution. (/) How does it compare with chlorine as a bleaching agent? 3. Action of chlorine on sodium bromide. Dissolve a bit of sodium bromide as large as a grain of wheat in 2 cc. of water. (g) What is the color of the solution ? Now add to the solution 1 cc. of chlorine water. The chlorine displaces bromine from sodium bromide just as zinc displaces copper from a copper salt (see displacement series, Exercise 35). (h) Account for the change in the color of the solution. 4. (i) Summarize the properties and conduct of bromine. EXERCISE 48 THE PREPARATION AND PROPERTIES OF IODINE Apparatus. Beaker (250-00.) and evaporating-dish as shown in Fig. 72 ; 2 test tubes ; stirring-rod. Materials. 4 g. sodium iodide (or potassium iodide) ; 4 g. powdered manganese dioxide; sulfuric acid; 2 cc. alcohol; 2 cc. carbon tetra- chloride; 10 cc. chlorine water (R.S.); 10 cc. starch solution (R.S.). 1. Preparation of iodine. Intimately mix on paper 3 g. of powdered sodium iodide and 2 g. of manganese dioxide. Place the mixture in the bottom of the beaker A (Fig. 72). Nearly fill the evaporating-dish B with cold water. Now remove the evaporating-dish, add 5 cc. of sulfuric acid to the mixture in the beaker, and stir it through the mixture ; then at once place the evaporating-dish back on the beaker as shown in the figure. Apply a very gentle heat to the mixture in the beaker, moving [83] B A \NaI \MnO, \H 2 S0 4 the burner about so as to heat the mixture uniformly. Note the colored vapor formed, which slowly condenses on the sides of the beaker and the bottom of the evaporating-dish in the form of grayish-black crystals. Finally withdraw the flame and let the beaker stand until the vapor is nearly all condensed. (a) What is the substance? (b) Account for its formation. (c) What property does the name of the substance suggest ? 2. Properties of iodine. By means of a glass rod transfer a little of the iodine collected on the sides of the beaker in i to a test tube half filled with water, and shake it for one or two minutes, (d) Is the iodine soluble in water (note the color of the water) to any extent? (Set the tube and contents aside for use in 4, below.) Repeat, using alcohol in place of water, (e) Compare the solubility of the iodine in water and in alcohol. (/) What is the solution in alcohol called.? Dissolve a small bit of the iodine in 2 cc. of carbon tetrachloride. (g) Note the color of the solution. 3. Action of chlorine on sodium iodide. Dissolve a bit of sodium iodide as large as a grain of wheat in 2 cc. of water in a test tube, (h) What is the color of the solution? Now add to the solution i cc. of chlorine water, (i) Account for the change in the color of the solution. 4. Action of iodine on starch. Place two test tubes in your test-tube rack and label them No. i and No. 2. Half fill each with starch solution. To No. i add a few drops of the aqueous solution of iodine reserved in experiment 2, above. To No. 2 add a bit of sodium iodide about as large as a grain of wheat and shake the mixture until the iodide dissolves. (;') Does free iodine change the color of starch solution?* (k) Does [84] FIG. 72. Preparing iodine by the action of sulf uric acid on a mixture of sodium iodide and sulfuric acid iodine in combination change the color of starch solution? Now add i or 2 cc. of chlorine water to tube No. 2 and shake the mixture. (/) Note and account for the results. (If the color is very deep, pour out a portion of the liquid and replace it with water.) 5. (m) Summarize the properties and conduct of iodine. EXERCISE 49 THE COMPOUNDS OF THE HALOGENS (CHLORINE, BROMINE, AND IODINE) WITH HYDROGEN Apparatus. 3 test tubes. Materials. A solution of sulfuric acid prepared by adding (care) 10 cc. of the concentrated acid to 2 cc. of water; i g. each of sodium chloride, sodium bromide, and sodium iodide; 3 strips of blue litmus paper. 1. Place three test tubes in your rack and label them No. i, No. 2, No. 3, respectively. In No. i put about i g. of sodium chloride, in No. 2 a like weight of sodium bromide, and in No. 3 the same weight of sodium iodide. Now add to No i, drop by drop, 2 cc. of the sulfuric acid, shaking the tube after each addition and waiting for the reaction to subside. Note that a colorless gas is evolved which escapes from the tube and attracts moisture from the air, forming a mist (this is more noticeable if you blow gently across the mouth of the tube}. Moisten a strip of blue litmus paper with water and hold it at the mouth of the tube, (a) What is the gas evolved (Exercise 29) ? (b) Write the equation for its formation. 2. In a similar way add 2 cc. of the sulfuric acid to tube No. 2, as directed above. Note the colorless gas evolved (blow gently across the mouth of the tube), (c) Test it with blue litmus paper as before, (d) What is the gas? (e) Write the equation for its formation. (/) Is a colored substance also formed in the reaction? (g) Recalling that hydrogen bromide is unstable, account for the formation of the colored substance. [85] 3. Now add 2 cc. of the sulfuric acid to tube No. 3. (h) Is a colorless gas formed as before (blow across the mouth of the tube) ? (i) Test with blue litmus paper as directed above. (j) What is the colored product formed (hydrogen iodide is even less stable than hydrogen bromide) ? (k) Do you recog- nize (odor) any gas evolved in addition to hydrogen iodide? (/) Account for the formation of this gas, recalling that hydro- gen iodide is unstable and that nascent hydrogen is a strong reducing agent. 4. (m) Why is the litmus paper used in the above experi- ments moistened before using? (n) Contrast in properties hydrogen chloride, hydrogen bromide, and hydrogen iodide. (o) Give the names of the aqueous solution of each. EXERCISE 50 THE SALTS OF THE BINARY ACIDS OF THE HALOGENS: CHLORIDES, BROMIDES, AND IODIDES Apparatus. 3 test tubes ; mortar and pestle. Materials, i g. each of sodium chloride, sodium bromide, sodium iodide; i cc. silver nitrate solution (R.S.); nitric acid; 10 cc. chlorine water (R.S.); 5 cc. carbon tetrachloride; 2g. manganese dioxide; sul- furic acid. 1. Test for chlorides, bromides, and iodides. Place three test tubes in your rack and label them No. i, No. 2, and No. 3, respectively. Put into No. i a bit of sodium chloride as large as a grain of wheat, in No. 2 put a like amount of sodium bro- mide, and in No. 3 the same amount of sodium iodide. Now add to each tube about 2 cc. of water and shake the mixtures until the solids are dissolved; then add to each tube 2 or 3 drops of silver nitrate solution, (a) Describe the results. (b) Write the reaction in each case. Add to each tube 4 or 5 drops of nitric acid and shake the mixture, (c) Does the pre- cipitate dissolve? The reaction with silver nitrate serves to detect the presence of chlorides, bromides, and iodides. [86] 2. How to distinguish between chlorides, bromides, and iodides. Arrange three test tubes as directed in experiment i, above. Thoroughly mix in a mortar a bit of sodium chloride as large as a pea with an equal amount of manganese dioxide and transfer the mixture to tube No. i. Put in tube No. 2 a similar mixture of sodium bromide and manganese dioxide, and in tube No. 3 a like mixture of sodium iodide and man- ganese dioxide. Set the tubes in the hood and add to each 4 or 5 drops of sulfuric acid. If the reaction is not marked, heat the tubes gently, (d) How can you distinguish between chlorides, bromides, and iodides? Again arrange three clean test tubes in your rack. Prepare in No. i a solution of sodium chloride as directed in experi- ment i, above; in a similar way prepare in tubes No. 2 and No. 3 a solution of sodium bromide and of sodium iodide re- spectively. Now add to each solution about i cc. of carbon tetrachloride (note that the tetrachloride does not mix with the water but sinks to the bottom of the tube). Shake the mix- tures and then set them in the rack for a few seconds until the liquids separate, (e) Note the color of the carbon tetra- chloride. Now add to each tube about 2 cc. of chlorine water and again shake the contents of the tubes vigorously ; then set the tubes aside until the liquids again separate. (/) Now note the color of the carbon tetrachloride. (g) What is the function of the chlorine water? (h) Describe in detail the method for distinguishing between chlorides, bromides, and iodides by using chlorine water and carbon tetrachloride. Note that the silver nitrate test will enable you to tell whether or not a given compound belongs to the group composed of chlorides, bro- mides, and iodides. Either the test with manganese dioxide and sulfuric acid or with chlorine water and carbon tetra- chloride will enable you to distinguish the three members of the group from each other. 3. Obtain from your instructor an unknown sample of a chloride, bromide, or iodide and determine its identity. [87] EXERCISE 51 THE PROPERTIES OF GASOLINE AND KEROSENE; ACETYLENE Apparatus. 2 test tubes ; 250-00. wide-mouthed bottle ; medicine dropper or pipette. Materials. Filter paper ; i cc. cottonseed oil ; wooden splint ; 3 cc. gasoline ; 3 cc. kerosene ; a bit of calcium carbide (CaC 2 ) the size of a bean. 1. Properties of gasoline and kerosene. (Gasoline is easily ignited. The student must keep it away from all flames.) Draw two circles (as large as a silver dollar) on a filter paper. Mark one circle G and the other K. Within the circle marked G place i drop of gasoline (use a medicine dropper) and within the circle marked K place i drop of kerosene. Suspend the paper so that both sides of the paper are exposed to the air, and note from time to time, (a) Which product is the more volatile ? Pour about 2 cc. of gasoline into a test tube and add 2 drops of some fat or oil such as cottonseed oil. (b) Does the oil dis- solve in the gasoline? (c) What use does this suggest for gasoline ? Pour about i cc. of gasoline into a test tube and add a like volume of water, (d) Do the two liquids mix? (e) Which is the heavier? (/) Repeat, using kerosene, (g) Can burning gasoline be extinguished by water ? Gently warm a 250-0:. wide-mouthed bottle by rotating it above a flame. Add to the warm bottle 2 or 3 drops of gasoline, place the palm of your hand tightly over the mouth of the bottle, and shake the bottle vigorously. Remove your hand and, standing at arm's length, bring a lighted splint to the mouth of the bottle, (h) Record the results, (i) What ap- plication of gasoline is based on the property noted in this experiment ? [88] 2. Acetylene. Nearly fill a test tube with water and drop into it a small piece of calcium carbide. (;) What is the gas evolved? (k) Write the equation for its preparation. (/) Ascertain by holding a lighted splint at the mouth of the tube whether the gas is inflammable. EXERCISE 52 SOME DERIVATIVES OF METHANE : CHLOROFORM, CARBON TETRACHLORIDE, IODOFORM Apparatus. Test tubes; beaker (ioo-cc.); glass rod. Materials. 2 cc. chloroform ; i cc. cottonseed oil ; 3 cc. carbon tetra- chloride ; splint ; 2 cc. alcohol ; 5 cc. iodine solution (R. S.) ; sodium hydroxide solution. 1. Chloroform, (a) Note its odor. Add about i cc. of chloro- form to an equal volume of water, (b) Does it mix with Water? (c) Is it heavier or lighter than water? Add 2 drops of an oil (such as cottonseed oil) to 2 cc. of chloroform, (d) Is chloroform a good solvent for oils? (e) Determine whether chloroform will burn by dipping the end of a glass rod into the liquid and then bringing it in contact with the edge of a flame for an instant. 2. Carbon tetrachloride. (/) Repeat all the experiments listed under chloroform, substituting carbon tetrachloride for the chloroform, (g) Pour about 2 cc. of carbon tetrachloride into a small beaker (100 cc.) and heat it until the vapor of the liquid fills the beaker ; then thrust a lighted splint into the vapor. Mention two important commercial uses of carbon tetrachloride illustrated in the above experiments, (h) What is the great advantage of carbon tetrachloride over gasoline as an agent in cleaning clothes? 3. lodoform. Pour about 2 cc. of alcohol into a small beaker and add 5 cc. of iodine solution. Now add to the mixture a solution of sodium hydroxide, drop by drop, stirring the liquid after each addition. Continue until the color of the iodine is [891 completely discharged. Note the formation of a yellowish solid (iodoform). (i) Note its odor. (;') What is the chief use of the compound ? EXERCISE 53 A STUDY OF FLAMES Apparatus. Wire gauze; porcelain dish; blowpipe. Materials. Charcoal (size of a bean) ; 5 cc. limewater (R. S.) ; can- dle; wooden splint; piece of charcoal 8x3x2 cm.; bit of lead as large as a pea; 2 g. lead oxide. 1. Parts of a flame, (a) Note and account for the difference between the combustion of a wooden splint and that of a piece of charcoal, (b) What are the con- ditions necessary for the production of a flame? (c) Light a candle and place it so that the flame is against a black background and is not dis- turbed by air drafts; then note the different cones in the flame. Test the relative tem- . .... FIG. 73. Using a blowpipe to form reducing and cxi- peratures of dif- dizing flames ferent parts of the flame by means of narrow strips of splints, (d) Draw a dia- gram in your notebook showing the different parts of the flame and noting the color of each of the cones. Extinguish the candle flame and hold a lighted splint 2 or 3 cm. from the wick in the little column of smoke rising from the wick, (e) Note and account for the result. [90] 2. Products of combustion. (/) What two elements consti- tute the main percentage of ordinary fuels? (g) What products form when these elements burn in air or oxygen? (h) Devise and describe simple experiments to show the presence of these products in the gases evolved by the burning candle. 3. Kindling temperature, (i) What is meant by the kindling temperature of gases? When a lamp is first lighted, a film of liquid often spreads over the chimney for an instant, (j) Ex- plain. Press a piece of wire gauze halfway down on a Bunsen flame. Notice that the flame does not extend above the gauze, (k) Is this due to the absence there of gases that are combustible (test for their presence by means of a lighted splint) ? Turn off the gas, then turn it on and ignite it over a piece of wire gauze held horizontally 4 or 5 cm. above the top of the burner. (/) Note the results and explain, (m) How does the miner's safety lamp prevent explosions? 4. Luminous flames. Hold a porcelain dish in a small lumi- nous Bunsen flame, (n) Account for the deposition of carbon. (0) Does the nonluminous flame deposit carbon? (p) To what is the luminosity of the flame due? Recall the experiment on the Bunsen flame in Exercise 2. 5. Use of the blowpipe. Close the openings on the Bunsen burner so as to secure a luminous flame ; then lower the flame until about 3 cm. high. Now place the end of the blowpipe just inside the lower part of the flame and blow gently through the blowpipe (Figs. 73, 74). The flame will be bent over, as shown in the figures. Practice this until you can produce a continuous and steady flame by forcing a portion of the exhaled [911 Reducing flame Oxidizing flame FIG. 74. Showing the location of the reducing and the oxidizing flames air through the blowpipe by constant tension of the muscles of the cheek. It will be noted that the flame so produced consists of two cones, one inside the other. The inner cone being rich in carbon monoxide is a reducing flame ; the outer cone being very hot and in contact with oxygen of the air is an oxidizing flame. Make a shallow cavity near the end of a piece of charcoal and place in this a bit of lead. Now heat this in the oxidizing flame as shown in Fig. 73. The lead is changed to lead oxide (PbO), a yellow solid which collects about the cavity on the surface of the charcoal. Clean the charcoal and place in the cavity a paste of lead oxide (PbO) made by adding a little water to 2 g. of the oxide and mixing. Now heat this in the reducing flame (hold the charcoal so that the oxide is in the tip of the inner cone). The oxide will be gradually reduced to a bead of metallic lead. NOTE. Save the charcoal for future experiments, but before return- ing it to your desk, pour some water into the cavity to extinguish any fire which may be smoldering in the interior of the charcoal; otherwise it is a source of danger from fire. Indeed, to avoid all danger from fire, it would be better if the charcoal used by the students were kept in some noncombustible vessel such as a crock or pneumatic trough. EXERCISE 54 SOME COAL-TAR COMPOUNDS (OPTIONAL) Apparatus. Test tubes; 25o-cc. flask, fitted with stopper and glass tube as shown in Fig. 75; glass rod; 25o-cc. beaker. Materials. 10 cc. benzene; 2 drops of cottonseed oil; nitric acid; sulfuric acid ; i or 2 cc. aniline ; 5 g. bleaching powder. NOTE. The student should first start experiment 2; while the liquids are being heated, experiment i can be performed. Caution. Benzene is very inflammable and must be kept away from all flames. 1. Benzene (C 6 H 6 ). (a) What is the distinction in com- position between benzene and benzine? (b) Note the odor [92] of benzene, (c) Add about i cc. of benzene to an equal vol- ume of water, (d) Does it mix with water? (e) Is it heavier or lighter than water? Add 2 drops of cottonseed oil to 2 cc. of benzene. (/) Is it a good solvent for oils? (g) Dip the end of a glass rod into the liquid and touch it to the edge of a flame for an instant, (h) Is benzene inflammable ? 2. Nitrobenzene (C 6 H 5 NO 2 ). Pour 8cc. of nitric acid into a 250-0:. flask and add (care), drop by drop, with constant motion of the flask so as to mix the liquids, 10 cc. of sulfuric acid, cooling the mixture all the time by allowing cold water to run on the outside of the flask. When the mixture is cold add, drop by drop, 6 cc. of benzene, mixing the liquids thoroughly after each addition of benzene. Now connect the flask with a cork and glass tube (Fig. 75) and heat the mixture very gently (not to boiling point). The tube acts as an air condenser to prevent the escape of the benzene. During the heating mix the liquids in the flask every few minutes by gently rotating the flask. Continue the heating for about half an hour ; then disconnect the flask, cool it, and pour the contents into a 250-0:. beaker filled with cold water. Stir the mixture with a glass rod, and after the oil (nitrobenzene) settles to the bottom, decant the clear liquid, leaving the oil in the beaker. Fill the beaker again with water, stir, and decant as before. In this way the acids are washed away, leaving the nitrobenzene pure. The nitric acid reacts with the benzene to form nitrobenzene and water as shown in the following equation: FIG. 75. Preparing ni- trobenzene by heating benzene and a mixture of nitric and sulfuric acids CEL + HNO, C 6 H 5 N0 2 [93] The sulfuric acid assists by absorbing the water formed in the reaction, (i) Record the color of the nitrobenzene; also its odor (poisonous if too much is inhaled) and density as com- pared with water. The above is the first step in the commercial production of aniline, which is the source material for many dyes. The nitro- benzene is converted into aniline by reducing it : C 6 H 5 NO 2 + 3H 2 > C 6 H 5 NH 2 (aniline) + 2H 2 O 3. Aniline (C 6 H 5 NH 2 ). (j) Note the properties (color, odor, solubility in water) of aniline. Add one drop of aniline to 100 cc. of water in a flask and shake the mixture. The aniline soon dissolves in the water. Place about i g. of bleaching pow- der in a beaker, add 2 5 cc. of water, and stir the mixture thor- oughly with a glass rod ; then filter and add i or 2 cc. of the filtrate to the aniline solution and mix thoroughly. If no change in color takes place, add more of the filtrate, 2 or 3 cc. at a time. (k) Record your results. This reaction serves as a delicate color test for aniline. EXERCISE 55 THE SUGARS Apparatus. 3 test tubes; 2 small beakers; stirring-rod. Materials. 10 cc. each of Fehling's solution A and B (R. S.) ; 5 cc. commercial glucose or corn sirup; 2 g. sucrose; i g. each of sweets such as candy, honey, molasses ; 2 or 3 g. sodium carbonate dissolved in as little water as possible; red litmus paper; hydrochloric acid. 1. The action of Fehling's solution on dextrose (grape sugar). The most common test for dextrose is the reaction with Fehling's solution. The latter is prepared by mixing equal volumes of solutions A and B, prepared as directed in the Appendix. Pour into a test tube about i cc. each of solutions A and B. When thoroughly mixed, the resulting solution should be deep blue, but perfectly clear. Heat the blue solution nearly to [94] boiling, add i or 2 drops of commercial glucose (corn sirup, procured at any grocery, will do as well), and continue the heating for a few moments. The copper sulfate in the solu- tion is reduced to cuprous oxide by the dextrose, and this separates in the form of a red or yellow solid. Levulose will act in the same way. Dissolve samples of candy, honey, and molasses in a little water and test for the presence of dextrose and levulose in these sweets, (a) Note the results obtained. 2. The action of Fehling's solution on sucrose. Try the action of Fehling's solution on sucrose as in i. (b) Note the results obtained. Now dissolve about 0.5 g. of the sugar in 5 cc. of water in a test tube and add 3 or 4 drops of concentrated hy- drochloric acid. Place the tube in a beaker of boiling water and leave it there for about five minutes; then pour the solution into a small beaker, cool the solution, and neutralize the acid present by adding a concentrated solution of sodium carbonate until the resulting mixture is just alkaline (test with red litmus paper). Now test this with Fehling's solution as in i. (c) Ac- count for the result. EXERCISE 56 THE COMPOSITION OF MILK Apparatus. Evaporating-dish ; stirring-rods. Materials. 150-00. milk; acetic acid (R. S.); Fehling's solution (R.S.) ; one half junket tablet (these tablets may ordinarily be obtained from any druggist; they may always be had at very little cost by ad- dressing Chr. Hansen's Laboratory, Little Falls, New York). 1. Determination of the solids and the water in milk. Place a short stirring-rod in a small evaporating-dish and accurately weigh the two together, recording the weights in the table below. Introduce about 20 cc. of milk and again weigh. Now evapo- rate the milk to dryness (Fig. 58), occasionally stirring it with the rod to break the scum (protein matter), which would other- wise retard evaporation. While the evaporation is taking place proceed with 2. [95] When the residue is perfectly dry, carefully wipe the outside of the dish, cool, reweigh, and record the weight. From your results calculate the percentages of solids and water in the milk. Pure milk contains not less than 12 per cent of solid matter. Consult your state laws as to the minimum amount of solid matter allowed in milk sold in the state. Weight of evaporating-dish and stirring-rod ... g. Weight of evaporating-dish, stirring-rod, and milk . g. Weight of milk taken (calculate) g. Weight of dish, rod, and residue left after evaporation g. Weight of solids in milk taken (calculate) .... g. Percentage of solids in milk taken (calculate) ... % Percentage of water in milk taken (ioo% % of solids) v ?, % 2. The separation of the protein (casein) in milk by rennin. Dissolve about one half of a so-called "junket" tablet in a little cold water and add the solution to about 100 cc. of sweet milk heated until just lukewarm. Stir the solution, then cool it and set it aside until the rennin contained in the tablet causes the separation of the curd (casein). Break up the curd by stirring, and filter it. Save the filtrate for further tests, (a) For what is the curd used? 3. The separation of the protein in milk by acid. Add i or 2 drops of acetic acid (vinegar will serve) to 5 cc. of milk, mix thoroughly, and set aside. The presence of an acid causes the casein to separate (hence the appearance of sour milk). 4. The separation of the lactose in milk. Evaporate the fil- trate reserved in 2, refiltering it if more solid matter separates. (b) Taste the residue, (c) Test it with Fehling's solution (Exercise 55). 5. (d) Enumerate the different constituents you have found in the milk. 96] EXERCISE 57 THE DETERMINATION OF THE FAT PRESENT IN MILK (OPTIONAL) Apparatus. A Babcock milk tester (Fig. 76) consisting of a centrifu- gal machine (^4), 2 test bottles (B), pipette made to deliver 17.6 cc. (C), and a small cylinder (D) graduated to hold 17.5 cc. ; beaker (5oo-cc.). Materials. Pint bottle of the milk to be tested ; sulfuric acid (con- centrated, density 1.82 to 1.83; the ordinary commercial sulfuric acid serves well) ; 100 cc. boiling water. NOTE. The most highly prized content of milk is the fat. This is sometimes in part removed by unscrupulous dealers and sold for cream or used in making butter; or water is added to the milk, which reduces -q ( IWfcri 10 - - # jal B )(- B } E D FIG. 76. The apparatus used in determining the percentage of fat in milk by the Babcock method the percentage of fat. To protect the public, laws have been passed by^ the different states as well as by the Federal government fixing the mini- mum percentage of fat in milk sold on the market. Normal milk con- tains from 3 per cent to 5 per cent of fat, averaging about 4 per cent. The laws of most of the states require not less than 3 per cent. The method ordinarily used for determining the fat in milk was devised by Professor Babcock and is known as the Babcock test. [97] In this test a definite volume of milk is mixed with sulfuric acid in a so-called test bottle, the neck of which is graduated so as to read per- centages of fat. The heat evolved in the mixing of the two is sufficient to destroy the casein of the milk but leaves the fat. The bottle is then whirled in a centrifugal machine; in this way the fat, being light, is finally drawn into the neck of the bottle, and the amount present can be read off. In order to balance the centrif- ugal machine properly it is neces- sary to have two test bottles, equally filled, opposite each other. Two different samples can therefore be tested at the same time, or in case only one sample is to be tested, both bottles can be filled with samples of the same milk, and the results compared. 1. Introducing the milk and acid into the test bottles. The milk to be tested is first mixed thoroughly by pouring it from the bottle into a beaker, and vice versa, three or four times. By means of the pipette, exactly i7.6cc. of the milk is then transferred to each of the test bottles, as shown in Fig. 77. Next fill the 17.5 cc. cylinder with the sulfuric acid to the graduation mark ; then, holding each of the test bottles in turn at an angle, slowly pour the 17.50:. of acid down the wall of the bottle, turning the bottle at the same time so as to wash down the neck of the bottle any milk .adhering to the wall. The acid, being heavier than the milk, sinks to the bottom of the bottle. 2. Mixing the acid and milk. The milk and acid in each bottle is now carefully mixed by gently rotating the bottle. Considerable heat is developed in the process. Care must be taken not to throw the mixture into the neck of the bottle. [98] FIG. 77. Showing the proper way of adding milk to the test bottle, determining the fat in milk Continue until the acid and milk are thoroughly mixed (the layer of acid at the bottom of the bottle must entirely dis- appear with the formation of a dark homogeneous liquid). 3. Separating the fat. The two bottles are at once placed opposite each other in the containers (E, E, Fig. 76) of the centrifugal machine, and the bottles whirled for four or five minutes. The rate of whirling varies with the machine (di- rections are given with each machine). The machine is then stopped, and hot (nearly boiling) water is added to each bottle until the liquid reaches nearly to the bottom of the narrow neck. The bottles are again whirled for one minute. The machine is again stopped, and hot water is added until the lower part of the fat column reaches about to the i or 2 per cent mark on the neck. The bottles are again whirled one or two minutes. The fat should now be clear and should come within the percentage marks on the bottle. By taking the lower and upper readings of the fat column and subtracting, the percentage of the fat in the milk is obtained. 4. (a) Give the results of your tests. EXERCISE 58 A STUDY OF STARCH Apparatus. Microscope; 2oo-cc. beaker; stirring-rod; 3 test tubes. Materials, i cc. of iodine solution (R. S.) ; o.i g. flour (largely wheat starch) ; 10 g. corn starch ; piece of bread ; hydrochloric acid ; 3 g. sodium carbonate dissolved in a little water ; red litmus paper ; starch solution (R.S.); Fehling's solution (R.S.) 1. Microscopic appearance. Examine under the microscope the appearance of starch from different sources (corn, wheat) when magnified, (a) Draw diagrams of the starch granules. 2. Actions of acids on starch. Try the action of starch solu- tion on Fehling's solution (as in Exercise 55). (b) Note your results. [99] Add 2 cc. of hydrochloric acid to 50 cc. of starch solution in a beaker and boil the contents gently for thirty minutes, allowing the solution to concentrate to about 2 5 cc. Cool the liquid, neutralize with sodium carbonate, and again test the solution with Fehling's solution, (c) Again note the results and explain. 3. Test for starch. Recall the action of iodine on starch (Exercise 48). This constitutes a good test for starch. Test different foods (such as bread, potatoes, and corn meal) for starch. To do this, boil about 5 g. of the food with 100 cc. of water, stirring the mass thoroughly so as to break it into small pieces ; then filter it and cool the filtrate. Now stir the filtrate with a glass rod, the end of which is first dipped into a solution of iodine. 4. The action of heat on starch. Place 3 or 4 g. of starch in a test tube and heat slightly for ten or fifteen minutes, stirring it often with a glass rod and regulating the heat so as not to burn the starch (the same results may be obtained by heating a piece of bread in an oven until it is dry and crisp). How does the product differ in taste from the original starch ? The heat changes a part of the starch into an isomeric compound known as dextrin, (d) For what is dextrin used? EXERCISE 59 TEXTILE FIBERS; PAPER Apparatus. 4 small beakers or test tubes ; stirring-rod ; (evaporating- dish; 2 large beakers; microscope; 2.5o-cc. flask fitted with stopper and tube as in Fig. 75). Materials. 3 strips each of uncolored cotton, pure wool (the kind known as nun's veiling is apt to be pure), silk, and linen cloth (3 cm. xiscm.); 50 cc. sodium hydroxide solution; strip of filter paper; hydrochloric acid ; sulfuric acid ; (3 strips of filter paper 2 cm. x 10 cm. ; ammonium hydroxide ; sodium hydroxide, desk solution ; piece of old white cotton cloth). 1. Effect of heat upon textile fibers. Ignite the end of a strip of cotton cloth in a Bunsen flame ; then withdraw it from the [100] flame, (a) Note the bdor;o? tlie 3&ftapg ;# dtii; (6) Does the cloth when ignited continue to burn? Repeat, using strips of wool, silk, and linen, (c) Can you distinguish in this way between vegetable fibers (cotton, linen) and animal fibers (wool, silk) ? 2. How to distinguish between vegetable fibers (cotton, linen) and animal fibers (wool, silk). Place a strip of each kind of cloth in small beakers, cover the cloth with sodium hydroxide solution, and boil the liquid for ten minutes, replac- ing the water as it evaporates (the cloth must always be com- pletely covered with the liquid) ; then set the beakers aside until cool, (d) Record the results. Cloth sold as woolen often contains considerable cotton, (e) How could you detect this adulteration? It will be of interest to test samples of woolen cloth to see if they are pure. 3. How to distinguish between the animal fibers. Immerse strips of silk and wool in concentrated hydrochloric acid and (/) note the change after they have stood a few minutes. 4. How to distinguish between the vegetable fibers. Immerse strips of cotton and linen in concentrated sulfuric acid for two minutes, (g) Record the results. 5. Miscroscopic appearance of textile fibers. Examine the appearance of each kind of fiber when magnified, (h) Com- pare with the diagrams given in your text. 6. Parchment paper. Pour 20 cc. of sulfuric acid (care} slowly and with constant stirring into a beaker containing locc. of water. Pour the solution into an evaporating-dish and allow to cool. Draw strips of filter paper slowly through the acid and then immerse them in a large beaker of water. Finally, wash the strips in a large beaker of water containing 5 or 10 drops of ammonium hydroxide. (i) When the strips are dry compare their properties with those of the untreated paper. 7. Paper pulp. Cut into short, thin strips a piece of old white cot- ton cloth. Introduce about 2 g. of these strips into a 25o-cc. flask and add about 20 cc. of a solution of the sodium hydroxide on your desk. Insert in the mouth of the flask a stopper through which passes a glass noii tube (Fig. 75) ; h%i? JiQ^tVtae flr.s-k until t'he liquid just boils, for two or three hours. When cool decant the liquid and wash the residue several times with water until it is free from sodium hydroxide. This residue is a form of pulp used in making fine writing paper. By beat- ing the pulp until it is very fine, straining it through a fine-wire sieve, and then pressing it with a hot iron, it is possible to obtain a coarse kind of handmade paper. EXERCISE 60 THE PREPARATION AND PROPERTIES OF COMMMON ALCOHOL Apparatus. One 2ooo-cc. flask (or bottle) connected with tube and bottle, as shown in Fig. 78 ; test tube ; stirring-rod ; apparatus shown in Fig. 57; evaporating-dish ; distilling apparatus (Fig. 41). Materials. 200 g. molasses or corn sirup ; cake of yeast ; 50 cc. lime- water (R. S.) ; 25 cc. alcohol ; small amounts (size of a pea) of sugar, starch, salt; i cc. cottonseed oil; 5 cc. iodine solution (R. S.) ; sodium hydroxide solution; soda lime (a mixture of sodium hydroxide and cal- cium hydroxide) sufficient to fill tube C (Fig. 78). 1. Preparation of alcohol. (It is suggested that this experi- ment be performed by the instructor or by students selected by the instructor ; after the alcohol is generated, the liquid may be di- vided among the differ- ent members of the class who will then test for the alcohol as directed in 4.) Dissolve about 200 g. of ordinary molasses (or sirup) in 2000 cc. of water in the flask A (Fig. 78). Grind a cake of yeast with a little water and add it to the solution in A. Connect the flask as shown in the figure (the bottle B contains limewater and the tube C contains soda [102] FIG. 78. Preparation of alcohol by the fermen- tation of molasses lime). Set the apparatus aside in a warm place (30 is best) for two or three days. Note that a gas is evolved in A and bubbles through the limewater in B. (a) Write the equation for the reaction taking place in A and B. 2. Properties of alcohol, (b) Determine the boiling point of alcohol, using the apparatus shown in Fig. 57. (c) Pour a few drops of alcohol into an evaporating-dish, ignite, and note the characteristics of the flame. (d) Determine whether alcohol is a good solvent for sugar, salt, starch, and oils, such as cottonseed oil. (e) Does alcohol mix with water. (/) Contrast the properties of alcohol with those of gasoline. 3. Test for alcohol. Pour 2 cc. of alcohol into a test tube and add to this 5 cc. of iodine solution. Now add a solution of sodium hydroxide, one drop at a time (mix after the addition of each drop), until the iodine color vanishes; then warm gently and set aside for a few minutes. A yellow precipitate of iodoform (Exercise 52), of characteristic odor, forms. (If the amount of alcohol present is small, the iodoform may not separate, but its presence will be revealed by its odor.) 4. When the fermentation of the sugar in A (Fig. 78) is complete, divide the liquid so that each student or group of students will have from 150 to 200 cc. Pour the liquid into a flask and distill (Fig. 41) 3 or 4 cc. (g) Dip the end of a glass rod in the distillate and touch it to the edge of a flame. Test the remainder of the filtrate for alcohol as in 3 above. EXERCISE 61 THE COMPOSITION OF FLOUR Apparatus. Beaker (500-0:.); porcelain crucible; pipestem triangle. Materials. 50 g. flour; iodine solution (R.S.) for testing for starch; cheesecloth (from 12 to 15 cm. square). 1. Weigh out about 25 g. of flour and mix with just enough water to form a stiff dough, working it in the hands until it [103] becomes smooth and elastic. Place the dough on a piece of cheesecloth, then fold the cloth about the dough and tie it with a string so as to form a little bag. Nearly fill your largest beaker with water, immerse the bag and contents in the water, and repeatedly squeeze the bag between the fingers. Note that the water becomes cloudy. Retain a portion of this cloudy liquid for tests in 2. Continue the washing in fresh portions of water until the resulting wash water remains clear. The action may be has- tened by working the dough in a small stream of running water. The residue is the nitrogenous constituent of flour and is known as gluten. Burn a portion of the gluten and (a) note the odor. 2. Test separate portions of the cloudy liquid reserved in i for starch (Exercise 58) and for sugar (Exercise 55). (b) Record your results. 3. Place about o.i g. of flour in a porcelain crucible, heat it with the Bunsen flame (Fig. 32), and gradually increase the heat until only a white residue remains. The residue is mineral matter. 4. (c) Enumerate the different constituents you have found in the flour. EXERCISE 62 THE ACTION OF PRESERVATIVES (OPTIONAL) Apparatus. Two 250-00. bottles or beakers; soo-cc. beaker; 2 test tubes. Materials. 300 cc. sweet milk ; drop of formalin ; 10 cc. hydrochloric acid to which is added one drop of a solution of ferric chloride (R. S.) ; i g. sodium benzoate ; loog. tomato catchup. 1. The action of formaldehyde on milk. Thoroughly clean two small bottles with hot water and half fill each with sweet milk. Add to the milk in one of the bottles one drop of formalin and mix thoroughly. Now pour about 3 cc. of milk from each of the two bottles into separate test tubes ; add to each an equal volume of the hydrochloric acid to which has been added one [104] drop of ferric chloride solution (the ordinary commercial hydrochloric acid serves the purpose well, since it usually con- tains a trace of ferric chloride as an impurity). Mix the contents of each of the tubes thoroughly and set them in a beaker of boiling water (Fig. 79). Note any change in color, (a) How can you detect the pres- ence of formaldehyde in milk? (b) What is the distinction between formalin and formaldehyde ? Set the two bottles containing the re- mainder of the milk aside and examine from day to day, noting when the milk in each becomes sour. 2. The action of sodium benzoate on tomato catchup. The student may like- wise study the action of sodium benzoate in preventing the fermentation of tomato catchup. Pour the catchup in small beak- ers, or bottles, adding the benzoate to one of the samples, mixing it thoroughly. Allow the samples to stand exposed to the air and (c) note which is the first to sour (odor and taste). In such cases the weight of the preservative added to the catchup should be from o.i to 0.2 per cent of the weight of the catchup. FIG. 79. Heating liquids in test tubes, by placing them in boiling water 105 EXERCISE 63 ACETIC ACID : A STUDY OF VINEGAR Apparatus. Evaporating-dish ; beaker (ioo-cc.); graduated test tube; (burette; graduated pipette ; 250-00. flask). Materials. 5 cc. acetic acid (R. S.) ; 30 cc. different kinds of vinegar, such as cider and distilled or white ; i cc. phenolphthalein solution (R. S.); ordinary desk sodium hydroxide solution; (sodium hydroxide solution of known strength. A so-called normal solution serves the pur- pose well. This contains 40 g. of the hydroxide in 1 1. of solution and may be purchased at any supply house). 1. The properties of acetic acid. Pour about 5 cc. of acetic acid into a small beaker, (a) Note its odor, (b) Test it with blue litmus paper, (c) Add to the acid about 50 cc. of water, mix thoroughly, and taste one drop. Now add to the dilute acid 2 or 3 drops of phenolphthalein solution and then add, drop by drop, the sodium hydroxide solution on your desk, stirring the liquid thoroughly after each addition. Continue until the solution is neutral (see Exercise 31). The reaction is expressed by the following equation : NaOH + H C 2 H 3 O 2 ^NaC 2 H 3 O 2 + H 2 O (acetic acid) (sodium acetate) The sodium acetate formed is a white solid which may be re- covered by evaporating the water, (d) To what class of com- pounds does sodium acetate belong ? 2. Determination of the solids in vinegar (quantitative). In this experiment different students should use different kinds of vinegar and compare results. Weigh a small evaporating^ dish and record the weight in Table I. Pour into the dish a definite volume (say 25 cc.) of vinegar. Evaporate the vinegar to complete dry ness (Fig. 58) ; then carefully wipe the bottom of the dish with a dry towel and again weigh, recording the weight in the table. [106] From your results calculate the amount of solid matter in TOO cc. of the vinegar. Pure cider vinegar should contain not less than 1.6 g. of solids in 100 cc. of vinegar (this is the limit fixed by the Federal government as well as by the statutes of many of the states). Distilled vinegar or white vinegar, on the other hand, contains only a trace of solid matter, (e) Note the odor and taste of the solid matter obtained from the vine- gar. The solids from pure cider vinegar should have an odor and taste suggestive of baked apples. The character of the solids varies according to the source of the vinegar. TABLE I Weight of evaporating-dish g. Weight of evaporating-dish and residue . . , . . g. Weight of solids (residue) in volume of vinegar taken (calculate) g. Weight of solids in 100 cc. of vinegar (calculate) . g. 3. Determination of the acidity of vinegar. The Federal statutes require that all vinegar sold shall contain not less than 4 g. of acetic acid in 100 cc. of vinegar. The amount of acid present may be deter- mined in the following way : Prepare or purchase a dilute solution of sodium hydroxide of known strength. If a normal solution of sodium hydroxide is used, dilute ex- actly 10 cc. of it to 100 cc. with water and mix thoroughly, i cc. of this diluted solution then contains exactly 0.004 g. of sodium hydroxide, which is a convenient strength to use. By means of a graduated pipette (or burette) run into a 25o-cc. flask exactly 5 cc. of the vinegar to be tested and dilute with about 50 cc. of water. Add to this 2 drops of phenolphthalein solution. Next fill a burette with the sodium hydroxide solution and run this, drop by drop, into the flask until the solution is neutral, following the directions given in Exercise 32. The liquids must be mixed after each addition of the hydroxide by gently rotating the flask. From the volume of sodium hydroxide solution used, calculate the weight of the hydroxide required to neutralize the acetic acid in the vinegar (see equation in i, above). From this result calculate the weight of acetic acid present in the 5 cc. of vinegar taken; then from this, the weight of acetic acid in 100 cc. of vinegar. (/) Record the results obtained in Table II. [107] TABLE II Weight of sodium hydroxide in i cc. of the solution used g. No. of cc. of hydroxide solution used to neutralize the acid in 5 cc. of vinegar Weight of sodium hydroxide required to neutralize the acid in 5 cc. of vinegar (calculate) ...... g. Weight of acetic acid in 5 cc. of vinegar (calculate) . . g. Weight of acetic acid in 100 cc. of vinegar (calculate) g. EXERCISE 64 ESTERS : FATS AND OILS Apparatus. 25o-cc. flask ; test tubes ; stirring-rod. Materials. 10 cc. glacial acetic acid (R.S.); sulfuric acid; 10 cc. alcohol ; 2 or 3 cc. fats and oils, such as cottonseed oil, olive oil, lard, butter, and cheese; 5 cc. carbon tetrachloride (R.S.) ; piece of white writing paper. 1. Preparation of a simple ester (ethyl acetate), (a) What is an ester ? Ethyl acetate is an example of a simple ester. It is a colorless liquid boiling at 78 and has a rather pleasant odor. It is derived from acetic acid (H C 2 H 3 O 2 ) by replacing one atom of hydrogen by the univalent radical known as ethyl (C 2 H 5 ). This change is easily brought about by heating acetic acid with alcohol, thus : H C 2 H 3 2 + C 2 H 5 OH >- C 2 H 5 C 2 H 3 O 2 + H 2 O (acetic acid) (alcohol) (ethyl acetate) Prepare ethyl acetate in the following way: Into a 250-0:. flask pour locc. of glacial acetic acid and add to it (care), drop by drop and with constant mixing, 5 cc. of sulfuric acid and then 3 cc. of alcohol. Apply a gentle heat to the mixture. Ethyl acetate is formed and may be recognized by its charac- teristic fragrant odor. Do not mistake the odor of alcohol for that of ethyl acetate (warm a few drops of alcohol in a test tube and note the difference between its odor and that of the ethyl acetate). The sulfuric acid assists in the reaction be- cause of its affinity for water. [108] 2. Composition and properties of fats and oils, (b) To what class of compounds do the fats belong? (c) Give the name and valence of the hydrocarbon radical present in fats, (d) Give the formulas and names of the three chief constituents of fats and oils, (e) What is the main difference in composition be- tween solid fats and oils? (/) Test the solubility of typical fats and oils in water, alcohol, and carbon tetrachloride as in Exercise 52. There is no simple accurate test for oils and fats, but the following, based on the fact that fats are nonvolatile, will serve fairly well: In different places on a piece of white writing paper rub one drop of various fats, such as cottonseed oil, cream, melted lard, and butter, (g) Note the appearance of the resulting spots when held in front of a light, (h) Heat the paper slightly to see if the spots will disappear, (i) Test different samples of cheese (warm a small piece and rub it on paper) and milk for fats by this method. EXERCISE 65 METHODS FOR DISTINGUISHING BETWEEN BUTTER AND OLEOMARGARINE (OPTIONAL) Apparatus. Iron spoon ; wooden splint (match stick will do) ; loo-cc. beaker. Materials. 10 g. each of fresh butter and oleomargarine (also process butter, if available) ; 50 cc. sweet milk. 1. Foam test. Over a small flame heat gently in a spoon 2 or 3 g. of the sample (butter or oleomargarine). Under these con- ditions butter will melt without sputtering and with the forma- tion of much foam on the surface, while oleomargarine will sputter and give but little foam. Process butter, or renovated butter (rancid butter which has been purified by melting the fat, skimming it off the surface, and churning it with milk under certain conditions), acts like oleomargarine, (a) Record the results of your tests. 2. Sweet-milk test. Pour 50 cc. of sweet milk into a small beaker and heat nearly to boiling. To the hot milk add 4 [109] or 5 g. of the sample and stir it with a wooden splint until the fat is melted, then place the beaker in ice water and continue the stirring until the fat solidifies. Under these conditions butter will solidify in the form of granules which mix with the milk. Oleomargarine, on the other hand, will collect in a single mass so that it can be removed from the milk in one lump with the wooden stirrer. (b) Record your results. EXERCISE 66 PROTEINS Apparatus. Evaporating-dish ; test tubes ; glass rod ; loo-cc. beaker. Materials. Small portion of white of an egg ; 25 cc. milk ; nitric acid ; ammonium hydroxide ; i g. flour ; small strip of woolen cloth. 1. Proteins. Place a small portion of the white of an egg (protein) in a test tube and heat it by dipping the tube into boiling water, (a) Record the results. Pour 20 cc. of milk into an evaporating-dish and heat gently. Note the scum that collects on the surface. Remove the scum with a glass rod, collect other portions of the scum in the same way, and save for further tests. Transfer a portion of the coagulated white of egg to a small beaker and moisten it with 2 or 3 drops of nitric acid, (b) Note any change, (c) Wash the egg free from acid with repeated portions of water, then moisten it with ammonium hydroxide and note change in color. These color changes serve as a test for protein matter. In the same way test for the presence of protein in the scum which separated when the milk was heated, (d) Test other substances for protein, such as flour, woolen cloth, a clipping of a finger nail, recording the results. Nitric acid stains the skin yellow ; (e) suggest an explanation for the change in color. Burn a small bit of different kinds of protein, such as egg, hair, the scum of milk (note the odor). (/) Record your results. [110] EXERCISE 67 PHOSPHORUS AND ITS COMPOUNDS Apparatus. 250-00. wide-mouthed bottle; deflagrating-spoon ; glass plate ; small beaker ; forceps. Materials. Phosphorus half the size of a pea (to be secured from your instructor when needed) ; litmus paper (red and blue) ; 10 cc. ammonium molybdate solution (R. S.) ; ammonium hydroxide ; nitric acid. 1. (Read carefully the precautions given for handling phos- phorus in paragraph 3, Exercise 8.) Cover the bottom of a wide mouthed bottle (250-00.) with water to a depth of about i cm. By means of your forceps place the piece of phosphorus on a deflagrating-spoon and ignite it by touching it with a hot wire. Quickly lower the phosphorus into the bottle and cover the mouth of the bottle with a glass plate. When the phos- phorus ceases to burn, withdraw the spoon and hold it in the Bunsen flame for a few seconds (to insure that all the phos- phorus is burned off the spoon). Cover the bottle with the palm of your hand and shake the water so that the fumes in the bottle are dissolved, (a) Test the solution with litmus paper, (b) What is present in the water? 2. Pour the solution in the bottle into a small beaker, add 2 or 3 cc. of nitric acid, and boil the solution until about half of it evaporates. The nitric acid oxidizes to phosphoric acid all the phosphorus compounds present. Add a few drops of the solution to 10 cc. of a solution of ammonium molybdate and warm gently, (c) Note the result (the compound formed has a very complex composition). Add ammonium hydroxide to the mixture until the liquid is alkaline, (d) Note the result. Again acidify the liquid with nitric acid, (e) Note the result. The formation of a yellow precipitate with ammonium molyb- date, which precipitate is insoluble in nitric acid and soluble in ammonium hydroxide, serves as a good test for phosphoric acid and its salts. [mi EXERCISE 68 SOME COMPOUNDS OF ARSENIC Apparatus. Hard-glass tube about 12 cm. long and 6mm. internal diameter, to be made by the student by sealing the end of a piece of hard-glass tubing (A, Fig. 80) ; magnifying-glass ; glass rod ; iron spoon. Materials. 0.2 g. arsenious oxide ; 2 or 3 g. charcoal in pieces about the size of a grain of wheat. 1. Reduction of arsenious oxide. Into the hard-glass tube introduce an amount of arsenious oxide equal in bulk to about 2 grains of wheat. Cover this to a depth of 2 or 3 cm. with the pieces of charcoal (Fig. 80), which have been previously heated to a high temperature in an iron spoon to expel any volatile mat- ter. See that the inner surface of the tube above the charcoal is per- fectly clean. Incline the tube, and heat (use low flame) the upper portion of the charcoal to a high temperature (Fig. 80) ; then, while maintaining the charcoal at this temperature, gradually bring the lower part of the tube also into the flame. The upper part of the tube must not be heated. The arsenious oxide is FIG. 80. Reducing arsenious ox- Changed into a vapor, which passes ide by hot charcoal over the hot charcoal and is re- duced. The resulting vapor of arsenic condenses on the colder portion of the tube just above the charcoal, (a) Note the appearance of the arsenic. [112] 2. Oxidation of arsenic. Cut the tube as near the bottom as possible and remove the charcoal, pushing it out at the bottom of the tube (if necessary) by a glass rod; then, inclining the tube at an angle of about 45, apply a very gentle heat to that portion of it which contains the deposit of arsenic. The air passing through the tube oxidizes the arsenic, forming small white crystals of As 2 O 3 , which are slowly deposited in the colder portions of the upper part of the tube, (b) Examine them with a magnify ing-glass, (c) Note their form. EXERCISE 69 A STUDY OF ANTIMONY Apparatus. Blowpipe; test tube; beaker (200-00.); stirring-rod; hydrogen sulfide generator (Fig. 68). Materials. Piece of charcoal (8 cm. x 3 cm. x 2 cm.) J 2 pieces of antimony (size of a grain of wheat) ; hydrochloric acid ; nitric acid ; strip of zinc half as long as a test tube and narrow enough to go in a test tube ; 5 g. ferrous sulfide. 1. Heat a bit of antimony on charcoal in the oxidizing flame (Fig. 73). The product is Sb 2 O 3 . 2. Into a test tube introduce a bit of antimony no larger than a grain of wheat and add about 3 cc. of hydrochloric acid and then 2 or 3 drops of nitric acid. After the metal has dis- solved, pour the solution into 100 cc. of water in a beaker. If a precipitate forms, add hydrochloric acid, drop by drop, with constant stirring, until the precipitate dissolves. Half fill a test tube with the resulting solution and insert a strip of zinc, as in Exercise 35. (a) Note the results. Through the remain- der of the solution pass a few bubbles of hydrogen sulfide (Exercise 42). The precipitate is Sb 2 S 3 . (b) Note its proper- ties. This is the compound often used in making red rubber. [113] EXERCISE 70 A STUDY OF BISMUTH Apparatus. Blowpipe; test tube; beaker (200-00.); stirring-rod; hydrogen sulfide generator (Fig. 68). Materials. 2 pieces of bismuth (size of a grain of wheat) ; piece of charcoal (8 cm. x 3 cm. x 2 cm.) ; nitric acid ; strip of zinc as in Exer- cise 69 ; 10 g. ferrous sulfide ; hydrochloric acid. 1. Heat a piece of bismuth on charcoal in the oxidizing flame (Fig. 73). Bi 2 O 3 is formed and is deposited on the charcoal. (a) What is the color of the oxide? (b) Write the equation for its formation. 2. Into a test tube introduce a bit of bismuth and add 4 or 5 drops of nitric acid. If the acid does not entirely dissolve the bismuth, add a few drops more. When the bismuth is dissolved, pour the solution into 100 cc. of water in a beaker. If a precipitate forms, add nitric acid, drop by drop, with constant stirring, until the precipitate dissolves. Half fill a test tube with the solution and insert in it a strip of zinc, as in Exercise 69. (c) Note the results. Through the remainder of the solution pass a few bubbles of hydrogen sulfide. The precipitate is Bi 2 S 3 . (d) Note its properties. 114] EXERCISE 71 COMPOUNDS OF SILICON Apparatus. Evaporating-dish ; stirring-rod. Materials. 2 cc. water glass (solution of Na 2 Si0 3 ) ; hydrochloric acid. 1. (a) Recall the formulas and names of the important acids of silicon. 2. Place 2 cc. of water glass (Na 2 SiO 3 ) in an evaporating- dish, dilute with 10 cc. of water, and add 2 or 3 cc. of hy- drochloric acid. Note the gelatinous precipitate of H 2 SiO 3 . (b) Write the equation for its formation. Evaporate the mix- ture to dry ness (Fig. 24) and heat the dish gently with the bare flame. The silicic acid is decomposed into water and sili- con dioxide, (c) Write the equation for the reaction. When cool, add water, filter, and examine the residue, (d) What is it? 3. (e) Recall the action of hydrofluoric acid on silica, writ- ing the equation for the reaction. EXERCISE 72 COMPOUNDS OF BORON Apparatus. Fine platinum wire (piece 5 cm. long fused in glass tube for handle, as shown in Fig. 81); beaker (ioo-cc.); stirring-rod; funnel; medicine dropper. Materials. 8 g. borax ; sulfuric acid ; i or 2 drops of cobalt nitrate solution (R.S.); filter paper. 1. (a) Write the names and formulas for three important compounds of boron. 2. Make a little loop on the end of a platinum wire and heat it to redness in a Bunsen flame; then quickly bring the loop in contact with some borax and reheat in the tip of the flame (Fig. 81). The borax adhering to the loop will swell up (owing to the expulsion of the water of hydration) and finally form a clear, glassy bead, (b) Note the color imparted to the flame. [115] Moisten the bead with a drop of sulfuric acid and again touch it to the edge of the flame, (c) Note the result. This serves as a simple test for borax. Moisten the bead with a drop of a solution of cobalt compound and re- heat until the bead is transparent when cold. (d) Note the color of the bead now (the depth of color depends upon the amount of cobalt pres- ent). This property serves as a simple test for co- balt. Some of the other metals likewise impart characteristic colors to the bead, as will be explained later. This method for detecting metals is known as the borax-bead test. 3. Dissolve 5 g. of borax in 150:. of boiling water. Care- fully add to the hot solution 2 or 3 cc. of sulfuric acid and stir. The sulfuric acid acts upon the borax as follows : Na 2 B 4 O 7 + H 2 S0 4 + 5H 2 O -r-+ Na 2 SO 4 + 4H 3 BO 3 The boric acid, H 3 BO 3 , is insoluble and separates as a pre- cipitate. Filter off the precipitate ; then place a bit of it on the loop of the platinum wire used in 2, above, and note the color it imparts to the flame, (e) Account for the test for borax given in 2. FIG. 81. Forming a borax bead 116 EXERCISE 73 COLLOIDS; EMULSIONS Apparatus. 5 test tubes; filter; 250-00. flask; funnel. Materials. Crystal of sodium thiosulfate; hydrochloric acid; filter paper; about i5g. clay or garden soil; dilute sulfuric acid made by adding 5 drops of sulfuric acid to 5 cc. of water (care) ; solution of aluminium sulfate (R. S.); 2 g. gelatin; white of egg; 5 cc. kerosene; sufficient thin shavings of white soap cut from a bar of soap to fill the bottom of a test tube to a depth of about 2 cm. 1. Dissolve a crystal of sodium thiosulfate about the size of a pea in 10 cc. of water and add i cc. of dilute hydrochloric acid. Note the separation of finely divided sulfur, which is formed in accordance with the following equation : Na 2 S 2 3 + 2HC1 > 2 NaCl + H 2 O + SO 2 + S {a) Is sulfur soluble in water? Filter the mixture, (b) Does the sulfur collect on the filter paper ? Allow the liquid to stand until the end of the hour, (c) Does the sulfur settle? (d) In what state is this sulfur? 2. Put a lump of moist clay or garden soil about the size of a small marble in a 250-0:. flask and add about 100 cc. of dis- tilled water. Stopper the flask and shake it vigorously. Allow the coarse material to settle for a few minutes. Pour off equal portions of the muddy water into three tubes marked respec- tively A, B, and C. Place tube A in the test-tube rack for comparison. To tube B add i or 2 cc. of dilute sulfuric acid. Shake it vigorously and set it beside tube A. To tube C add i or 2 cc. of a solution of aluminium sulfate and shake the tube vigorously ; then set the tube in the rack with the other two. (e) Note the rate at which suspended material in the three tubes settles. Any electrolyte will serve in place of the two reagents you have used. (/) Why does a river emptying into the ocean fill up at its mouth ? [117] 3. Place in a test tube a sufficient amount of small pieces of dry gelatin to make a layer i or 2 centimeters in depth. Add about 10 cc. of water and heat the water until a clear liquid is obtained. Now immerse the tube in ice water and note the formation of a gel. Again heat the substance until a clear liquid is obtained, and then repeat the cooling process, (g) Does the gel "set" again? 4. Add a small portion of the white of an egg to 10 cc. of cold water and shake the mixture thoroughly. The albumen of the egg is present in the water in the form of a colloid. Divide the mixture into two equal portions. Heat the one portion to boil- ing, (h) Is the colloid precipitated? To the other portion add 2 or 3 drops of nitric acid, (i) Note the results. Make suitable test to determine whether the coagulation of the albumen of the egg is a reversible process. 5. Select two test tubes of the same size. Place in the bot- tom of one to a depth of about 2 cm. some thin pieces of white soap cut from a bar of soap ; then fill the tube about two thirds full of distilled water. Warm the mixture and shake it gently until the soap dissolves. Now fill the other tube about two thirds full of water. Next pour into each tube about 2 cc. of kerosene. Note that the oil floats on the top of the water in each tube. Now take a tube in each hand, close the mouth of the tube firmly with your thumb, and shake the tube and contents vigor- ously for one minute. (;) Note the appearance of the liquids in each tube, (k) What is such a mixture called? Set the tubes aside five or ten minutes (or until the next laboratory period) and again examine the liquids in the tubes. (/) Have the oil and water separated in both tubes? (m) What term is applied to a substance, such as soap, that prevents or at least delays the separation of the liquids in an emulsion ? [118] EXERCISE 74 GENERAL METHODS FOR THE PREPARATION OF THE COMPOUNDS OF THE METALS Apparatus. 6 test tubes. Materials, o.ig. of each of the following salts, dissolved in 5 cc. water: (i) calcium chloride, (2) lead nitrate, (3) barium chloride, (4) ferric chloride, (5) silver nitrate, (6) potassium iodide (solutions of any of these on the Reagent Shelf may be used) ; sodium carbonate solution (R.S.); hydrochloric acid; sulfuric acid; ammonium hydroxide. 1. By the direct union of the elements. Recall the formation of sulfides of copper and of iron (Exercise 40) ; of the chloride of antimony (Exercise 28). (a) .Write the equations for the reactions involved. 2. By dissolving a metal or its hydroxide in appropriate acids. Recall the formation of zinc sulfate (Exercise 9) ; of sodium chloride (Exercise 31) ; of copper nitrate (Exercise 37). (b) Write the equations for the reactions, (c) When a metal or its hydroxide is acted upon by an acid, what becomes of the metal? 3. By acting upon a salt of an acid with an acid having a higher boiling point. Recall the action of sulfuric acid upon sodium nitrate (Exercise 37) ; of hydrochloric acid upon iron sulfide (Exercise 41) ; of sulfuric acid upon fluorides (Exer- cise 46) ; of sulfuric acid on chlorides (Exercise 29) ; of hydrochloric acid on carbonates (Exercise 33). (d) Write the equations for each reaction and show in what respects they are all similar. 4. By the decomposition of a compound. Recall the action of heat upon potassium chlorate (Exercise 7) ; upon copper nitrate and lead nitrate (Exercise 38). (e) Write the equations for the reactions involved. 5. The following compounds are insoluble (see Appendix, Table of Solubilities of some of the compounds of the metals) : [ 119 ] calcium carbonate (CaCO 3 ), lead sulfate (PbSO 4 ), barium carbonate (BaCO 3 ), ferric hydroxide ( Fe ( OH ) 3 ), silver chlo- ride (AgCl), lead iodide (PbI 2 ). Prepare a small amount of each in a test tube. (/) Write the equation for the reaction involved in each case. EXERCISE 75 THE COMPOUNDS OF SODIUM Apparatus. Evaporating-dish ; beaker ; watch glass ; stirring-rod ; hard-glass test tube; platinum wire; piece of cobalt glass 10 cm. square; magnifying-glass. Materials. 5 g. sodium carbonate ; litmus papers (red and blue) ; hydrochloric acid ; sulfuric acid ; 2 or 3 clear crystals of Glauber's salt ; 3 g. sodium bicarbonate ; i cc. limewater (R. S.) ; 2 g. sodium chloride. 1. Recall experiments with sodium (Exercise 30). 2. Dissolve 5 g. of sodium carbonate in 20 cc. of water. Test the solution with red and with blue litmus paper, (a) Account for the results. Now convert the so- dium carbonate present into common salt, (b) Describe the method and write the equation for the reaction involved. Treat some of the salt so pre- pared with sulfuric acid. (c) What gas is evolved? 3. (d) Write the com- plete formula for Glau- ber's salt. Select some clear crystals of the salt, place them on a watch glass, and expose them to the air for one hour or more, (e) Note the change. The change is due to the fact that some of the water of hydration escapes. Crystals that behave in this way are said to be efflorescent. [120] FIG. 82. Method of making a flame test 4. Fill a hard-glass test tube about one fourth full of sodium bicarbonate and heat gently. Prove that carbon dioxide is evolved (Fig. 54). What liquid condenses in the colder part of the tube? (/) Write equations for the reactions by which so- dium carbonate is converted into the bicarbonate and vice versa. 5. Bend the end of a platinum wire into the form of a small loop and hold it in the lower part of the outer film of the Bunsen flame (Fig. 82) until it ceases to give any color to the flame; then dip it into a solution of a compound of sodium so that a drop of the solution is suspended in the loop ; then hold it in the Bunsen flame as before, (g) Note the color, (h) Note the appearance of the sodium flame when viewed through a piece of cobalt glass. 6. (i) Recall the action of hydrochloric acid on sodium thio- sulfate (Exercise 73, i). 7. Dissolve about 2 g. of sodium chloride in a little water in a beaker and set the uncovered solution aside until the next laboratory period; then (;) examine the shape of the crystals with a magnifying-glass. Save the crystals for reference in a future exercise. EXERCISE 76 THE DETERMINATION OF THE WEIGHT OF COMMON SALT OBTAINED BY ADDING HYDROCHLORIC ACID TO A DEFI- NITE WEIGHT OF SODIUM BICARBONATE (OPTIONAL) Apparatus. Evaporating-dish and watch-glass cover; medicine drop- per; beaker; stirring-rod; balance. Materials, i g. sodium bicarbonate ; hydrochloric acid. 1. Carefully weigh to o.oi g. the evaporating-dish and watch glass, recording the weight in the table below. Transfer to the dish about i g. of sodium bicarbonate and reweigh, recording the weights. Pour 4 or 5 cc. of water on the bicarbonate, and place the watch glass on the dish so that only the lip of the dish remains uncovered. Using a medicine dropper or pipette, drop down the lip of the dish 2 or 3 drops of hydrochloric acid. [1211 Wait until the effervescence caused by the escape of the carbon dioxide ceases, then add a few drops more of the acid. Repeat until the addition of the acid no longer causes any effervescence. Now hold the watch glass in the hand just above the dish, and with a little water carefully rinse back into the dish the liquid which has collected on the undersurface of it. Remove the watch glass and slowly evaporate the solution (Fig. 58). When the solution has evaporated nearly to dryness, cover the dish with the watch glass and heat the dish with the tip of the flame. Continue the heating until there is no more liquid left in the dish or clinging to the undersurface of the glass. Then withdraw the heat and, after the dish is cool, reweigh the dish, watch glass, and residue (sodium chloride). From your results calculate the amount of salt formed from i g. of the bicarbonate, recording the weights. Make the cal- culations called for in the following table : Weight of evaporating-dish and watch glass .... g Weight of evaporating-dish and watch glass plus sodium bicarbonate g. Weight of sodium bicarbonate (calculate) .... g. Weight of dish, watch glass, and sodium chloride . . g. Weight of sodium chloride (calculate) g- Theoretical weight of sodium chloride that can be ob- tained from the weight of sodium bicarbonate taken g. [122] EXERCISE 77 SOME COMPOUNDS OF POTASSIUM Apparatus. Evaporating-dish ; stirring-rod; beaker (250-00.) ; cobalt glass; platinum wire; (funnel). Materials. locc. potassium hydroxide solution (R.S.); hydrochlo- ric acid; 0.5 g. potassium chloride; (iyg. sodium nitrate; i5g. potas- sium chloride; filter paper). 1. Pour 10 cc. of a solution of potassium hydroxide into an evaporating-dish, neutralize with hydrochloric acid, and evapo- rate to dryness. (a) What is the product? (b) By what other method have you prepared this same compound in a former exercise ? 2. Repeat 5, Exercise 75, using a solution of potassium chloride, (c) Note the appearance of the flame, (d) Also note the appearance of the flame through a piece of cobalt glass. (e) What is the difference in the appearance of the sodium flame and of the potassium flame when viewed through the cobalt glass? (/) How could you detect both sodium and potassium if they were present in the same solution? 3. Preparation of potassium nitrate. Dissolve 17 g. of sodium nitrate in 15 cc. of boiling water ; also 15 g. of potassium chloride in 30 cc. of boiling water. Mix the two solutions in a small beaker and evaporate (stirring the mixture) to about 20 cc. ; then quickly filter the hot solu- tion and set the filtrate (Filtrate A) aside until cold. The reaction between potassium chloride and sodium nitrate is re- versible, and the number of grams of each of the four compounds in- volved which dissolve in 100 g. of water at 15 and 100 is as follows : 15 100 15 100 Sodium nitrate . . 84 180 Potassium nitrate . 26 246 Potassium chloride .33 57 Sodium chloride . 36 40 From a study of these solubilities (g) what compound should you expect would separate when the hot solutions of sodium nitrate and potassium chloride are mixed together? (h) Examine the crystals on [123] the filter paper with a magnifying-glass and compare with 7, Exercise 75, to see if your conclusion is correct, (i) Taste the crystals. (;) What solid should you expect would separate from Filtrate A when it is cooled ? (&) Should you expect it to be pure ? Filter off the solid and examine it with a magnifying-glass. (/) Can you detect crys- tals of sodium chloride in this solid ? Dissolve the solid in as little hot water as possible, cool the solution, and again filter off the solid. Repeat until no crystals of sodium chloride can be detected. Prove the identity of this compound (test for potas- sium by the flame and for a nitrate by 2, Exercise 38). EXERCISE 78 THE PROPERTIES OF AMMONIUM COMPOUNDS Apparatus. Evaporating-dish and watch-glass cover ; 5 test tubes. Materials. Ammonium hydroxide; hydrochloric acid; sodium hy- droxide solution; litmus papers (red and blue); (0.2 g. ferrous sulfate solution (R.S.); ammonium carbonate (R. S.); barium chloride (R. S.); calcium chloride (R.S.)). 1. Pour 10 cc. of ammonium hydroxide into an evaporating- dish, neutralize with hydrochloric acid, and evaporate just to dryness (Fig. 58). (a) What is the residue? (b) Note its odor. Introduce about one half of the residue into a test tube, add a few drops of sodium hydroxide solution, and heat gently. (c) Note the odor of the evolved gas and its action on a moist strip of red litmus paper. All ammonium compounds evolve ammonia when heated with sodium hydroxide. This reaction serves as a good test for all ammonium compounds. Cover the evaporating-dish containing the remainder of the residue with a watch glass and heat gently with a small flame. Note that the solid sublimes ; that is, passes directly from the solid form into a vapor which condenses (partly) on the cold surface of the watch glass. 2. Add a few drops of ammonium carbonate solution to separate solu- tions of a compound of barium and of calcium, (d) Write the equation, for the reaction in each case. [124] 3. Add 2 or 3 drops of ammonium sulfide to 5 cc. of a solution of ferrous sulfate. (e) Note the result and write the equation for the re- action that takes place. Repeat, using hydrogen sulfide solution in place of ammonium sulfide. (/) Account for the difference in the reaction (consult Table of Solubilities in Appendix). EXERCISE 79 DETECTION OF COMPOUNDS OF THE ALKALI METALS (OPTIONAL) 1. Recall such reactions of sodium, potassium, and ammo- nium compounds; also of carbonates, sulfates, nitrates, chlo- rides, bromides, iodides, and phosphates as will serve to identify them, and outline a method of procedure for the identification of them. Then ask the instructor for unknown compounds falling within this list and identify them, recording your results. EXERCISE 80 THE PREPARATION AND PROPERTIES OF SOAP Apparatus. Evaporating-dish ; large beaker ; stirring-rod ; funnel ; small beaker; 4 test tubes. Materials. 10 cc. alcohol ; 5 g. cottonseed oil (or lard) ; i g. sodium hydroxide dissolved in 2 cc. water; filter paper; hydrochloric acid; mag- nesium sulfate (R.S.); calcium chloride solution (R.S.); i g. sodium chloride dissolved in 5 cc. water. 1. Add 10 cc. of alcohol to 5 g. of cottonseed oil in an evaporating-dish. To the resulting mixture add i g. of sodium hydroxide dissolved in 2 cc. of water. Evaporate carefully (use small flame and do not let the tip touch the dish), stirring the mixture constantly until the odor of alcohol can no longer be detected, (a) Write the equation for the reaction on the sup- position that the oil is composed of olein only, (b) What is the process called? (c) What remains in the dish? 2. Add 50 cc. of distilled water to the residue in the dish, stir well for a few minutes, and filter, if not clear. Pour a few drops of the filtrate on your hands and rub them (add more distilled (125 \ water if necessary) to see if the soap lathers freely. Pour 5 cc. of the filtrate into each of three test tubes. To the first add 2 or 3 drops of hydrochloric acid ; to the second add a few drops of a solution of magnesium sulfate. In like manner add a few drops of a solution of calcium chloride to the third, (d) Note what takes place in each test tube, writing the equations for each of the reactions, (e) Why do waters containing calcium and magnesium compounds (hard waters) form a precipitate (curdle) with soap? .3. Add a few drops of sodium chloride solution to 10 cc. of the filtrate obtained in 2. The soap in the filtrate is not in solu- tion but in colloidal suspension. The salt causes the precipita- tion of the colloid (soap). (/) What advantage is taken of this reaction in the manufacture of soap ? 4. Recall the effect of soap in the formation of emulsions (Exercise 73). (g) What influence has this property upon the cleansing action of soap ? EXERCISE 81 A STUDY OF SOME OF THE COMPOUNDS OF CALCIUM Apparatus. Blowpipe and charcoal ; 2 test tubes ; glass tubing for blowing air through solution ; evaporating-dish ; watch glass ; copper penny; piece of window glass; 25o-cc. flask; platinum wire for flame; test; (spectroscope). Materials. 3 g. marble; hydrochloric acid; ammonium carbonate (R. S.); drop of cottonseed oil; log. plaster of Paris; log. commer- cial cyanamide; red litmus paper; o.i g. of the chloride or nitrate of each -of the metals calcium, strontium, barium (o.i g. each of sodium chloride and potassium chloride). 1. Place one or two small pieces of marble about as large as a bean on a piece of charcoal and heat them for five minutes in the oxidizing blowpipe flame (Fig. 73). When cool drop the resulting mass into 10 cc. of cold water in a test tube, (a) What evidence have you of a chemical reaction taking place ? Shake the tube for about one minute; then filter and collect the fil- [126] trate. Now gently blow exhaled air through the clear filtrate. (b) Note all the changes and write the equations for the three reactions that have taken place. 2. Dissolve i or 2 g. of marble in hydrochloric acid, (c) Write the equation for the reaction, (d) What does the effervescence indicate? Evaporate the solution to dryness (use the bare flame and evaporate to complete dryness). (e) What is the composition of the residue? Place a small piece of it on a watch glass and expose it to the air for an hour or more (it may be left until the next laboratory period). (/) Account for the results. Dissolve the remainder of the residue in the evaporating-dish in 5 cc. of water (filter if not clear) and add to it a few drops of ammonium carbonate, (g) Note the results and write the equation for the reaction involved. 3. Place on a glass plate a penny that has been rubbed with a drop of oil. Pour over the coin a thick paste made by adding a little water to plaster of Paris. Set the glass plate aside until the paste hardens; then remove the coin and (h) note the results. 4. Place about one tablespoonful of commercial cyanamide in a 25o-cc. flask, add 50 cc. of water, and heat to boiling. Suspend a strip of red litmus paper just inside the flask and note any change in color, (i) What do the results indicate? (;') Can you detect the odor of ammonia in the escaping steam? Account for its formation, (k) What is the original source of the nitrogen present in the ammonia that is evolved (recall the method of making the cyanamide) ? 5. Try the flame tests for each of the following metals as in 5, Exercise 75 (use the chloride or nitrate of each metal) : calcium, strontium, barium. (/) Record the results below. METAL COLOR OF FLAME Calcium . . . . . . Strontium . . .,,-.'. . . Barium [1271 6. The use of the spectroscope. The spectroscope is an instrument which has been of great service in many chemical investigations, es- pecially in the discovery of new elements and in detecting the presence of known elements in complex mixtures. The principle involved in its construction is as follows : When a beam of light passes through a triangular prism of glass, it is bent out of its course and emerges at a decided angle with its original direction, as shown in Fig. 83. Ordinary light is made up of many different wave lengths, and each one is deflected, or refracted, to a dif- ferent degree, so that the various colors of which the light is composed are spread out in a series, the red being the least refracted, the violet the most so. A beam of white light gives a continuous series of colors from red through orange, yellow, green, blue, to violet, called a con- tinuous spectrum. When many of the elements (or their compounds) are volatilized at a high temperature, as in the heat of the Bunsen flame, colored lights are obtained, each metal having its own characteristic color. These lights differ from white light in that they are not made up of so many different wave lengths ; hence when passed through the prism the spectrum obtained is not continuous, but merely shows those colors of which the light is composed. That these colors may be made as distinct and as sharply separated as possible, the light should shine upon the prism through a very narrow slit in a screen, arranged so as to be parallel with the axis of the prism. The colors will then be a series of narrow lines, each an image of the slit, spread out parallel with each other. An instrument, the essential parts of which are a prism, a screen provided with a narrow slit, and lenses for focusing the light upon the slit and for viewing the spectrum, is called a spectroscope, or spectrometer. Fig. 84 represents a simple form of such a spectroscope, the slit being seen at the end of the tube B. The light from the Bunsen burner passes through the slit in the tube B, is separated into its different wave lengths by the prism at the center of the spectroscope, and is seen by looking through the tube A. The tube C contains a scale illuminated by a flame at the end of the tube ; this scale makes it possible to fix the position of any lines in the spectrum. Make the following tests with the spectroscope: [128] FIG. 83. When passed through a prism a ray of white light is sepa- rated into the different colors which together compose the white light First use the luminous Bunsen flame. In this the light is caused by solid particles of carbon, and the spectrum of this will be a continuous band when viewed through A. Next examine the spectrum of one or more of the following metals : potassium, sodium, calcium, strontium, barium, using in each case a volatile compound of the metal, preferably the chloride or nitrate. To do this the nonluminous Bunsen flame must be used. First clean the platinum wire until it will impart no color what- ever to the flame. Then dip the loop at the end of the wire into a concentrated solution of sodium chloride and bring the loop into the FIG. 84. A spectroscope lower edge of that part of the Bunsen flame which is next to the tube B, as shown in the figure. The spectrum will be found to consist of a single band of yellow light. The slit at the end of the tube B should be ad- justed by the attached screw until the band is narrow and sharp. In the same way examine the spectrum produced by the other metals mentioned above. It is, of course, essential that the wire be thoroughly cleaned each time; otherwise we will obtain the spectrum of two or more of the metals. It will be found that with the exception of sodium the other metals mentioned will give more than one band of light, (m) Diagram the results obtained for each of the metals. [129} EXERCISE 82 THE PROPERTIES OF BLEACHING POWDER Apparatus. 2 small beakers ; stirring-rod ; carbon dioxide generator (Fig. 53); funnel; test tube. Materials. 25 g. bleaching powder (see that the bleaching powder comes from air-tight cans; otherwise the powder is apt to be worth- less) ; 10 g. marble and hydrochloric acid for generating carbon dioxide ; filter paper; narrow strips of different samples of colored calico. 1. The active agent of commercial bleaching powder is the compound CaOCl 2 . In addition to this compound the com- mercial powder contains a certain amount of calcium hydroxide and certain other impurities present in the lime from which the bleaching powder was made. When sulfuric acid is added to bleaching powder both hydro- chloric acid and hypochlorous acid (HC1O) are formed. These two react as fast as generated, however, to form water and chlorine. The equations for the reactions are as follows : CaOCl 2 + H 2 S0 4 + CaS0 4 + HC1 + HC1O HC1 + HC1O + H 2 O + C1 2 A very weak acid like carbonic acid, on the other hand, liber- ates only hypochlorous acid as follows : 2CaOCl 2 + H 2 CO 8 > CaCO 3 + CaCl 2 -I- 2HC1O This is the reaction that takes place when bleaching powder is exposed to the air, the carbonic acid being formed from the moisture and carbon dioxide present in the air. Hypochlorous acid is a good bleaching and disinfecting agent. To test its bleaching property, proceed as follows : Pour 50 cc. of water over 2 5 g. of bleaching powder in a beaker. Stir the mixture for two or three minutes ; then filter. The active agent of the powder, CaOCl 2 , is now present in the filtrate. Now pass through the filtrate a slow current of carbon [130] dioxide as long as a precipitate continues to form ; then filter. (a) What compounds are present in the filtrate? Immerse some strips of colored cloth in the filtrate for a few minutes. (b) Record your results. EXERCISE 83 HARD WATERS AND METHODS FOR SOFTENING THEM Apparatus. 6o-cc. bottle; carbon dioxide generator (Fig. 53); fun- nel; 2 test tubes; small beaker. Materials. 30 cc. limewater (R.S.) ; bit of soap dissolved in water; 10 to i5g. of marble and hydrochloric acid for generating carbon dioxide; i g. magnesium sulfate (R.S.) ; filter paper; i g. sodium car- bonate dissolved in as little water as possible ; i g. powdered calcium sulfate. 1. Bubble carbon dioxide into 250:. of limewater diluted with an equal volume of water. Note that a precipitate forms which gradually dissolves as more of the gas is passed through. (a) Account for the results, writing the equations for the re- actions involved. The resulting liquid is a good sample of a hard water. Add a few drops of a soap solution to 5 cc. of the hard water and (b) note the results. Divide the remainder of the hard water into two parts. Gradually boil the one part, (c) Note and account for the result. To the other part add a few drops of clear limewater and mix intimately, (d) Again note and account for the result. 2. Shake i g. of calcium sulfate with 10 cc. of water in a test tube for two or three minutes; filter, and add to the filtrate 2 or 3 drops of a saturated solution of sodium carbon- ate, (e) Note and account for the results. All hard waters contain more or less calcium acid carbonate, calcium sulfate, calcium chloride ; also the corresponding com- pounds of magnesium. (The methods used for removing the calcium compounds likewise serve for removing the magnesium compounds.) (/) How could such waters be softened on a [131] large scale? (g) Waters softened in this way would contain what compounds in solution ? 3. Test some hard waters from wells by the above methods and (h) give the results obtained. EXERCISE 84 TESTING THE ACIDITY OF SOILS Apparatus. Watch glass; ordinary kitchen knife with thin blade so that it will readily bend; forceps; (25o-cc. flask; tripod). Materials. Cupful of soil to be tested ; strips of blue and red litmus papers; (i g. barium chloride mixed with o.i g. zinc sulfide; strip of filter paper (about 6 cm. x i cm.) moistened with a solution of lead ace- tate (R.S.)). 1. Soils under cultivation tend to become acid, and most crops do not thrive in acid soil; hence the custom of adding lime to soils. The following is a simple way of finding out whether or not a given soil is acid : Collect about one cupful of an average sample of the soil. By means of a clean knife blade mix the soil intimately. Now take one strip each of red and blue litmus paper (use your for- ceps to avoid any secretion from your fingers from coming in contact with the papers) , moisten the papers with distilled water and press them side by side against the concave face of a watch glass. Pour over the strips 2 or 3 tablespoonfuls of the soil ; then add distilled water, a little at a time, and gently mix the water through the soil with a clean knife blade (be careful not to displace the red and blue litmus papers) until there is formed a thick paste which will cling to the watch glass when inverted. The glass is now inverted and placed on the desk so that the strips of litmus paper are visible. After fifteen or twenty minutes note if any change in the color of the litmus paper has taken place, (a) Record the results of your tests of different soils, (b) What precautions must be taken in order to secure reliable results? [132] 2. A method of testing soils largely used at the present time was de- vised by Professor Truog of the University of Wisconsin and is known as the " Truog test." Proceed as follows : Collect a sample of soil as in experiment i and introduce 12 or 15 g. of the soil into a 25o-cc. flask. Next add to this i g. of the barium chloride zinc sulfide mixture (see materials). Pour into the flask 100 cc. of distilled water and shake the flask very gently. Heat the mixture, using a flame that will cause the liquid to boil in from five to seven minutes. Sometimes the liquid froths just when it begins to boil; in case it begins to froth, withdraw the heat for a moment until the frothing subsides. After the liquid in the flask has boiled for just one minute, place across the mouth of the bottle, as shown in Fig. 85, a strip of lead acetate paper and hold it in this position for two minutes, while the boiling continues; then remove the paper and withdraw the heat. If the soil is acid, hydrogen sulfide will be lib- erated and will act upon the lead acetate, forming black lead sulfide (PbS). The greater the acidity, the greater the amount of lead sulfide formed, and hence the darker the paper. Since the test is very delicate it is essential that care be taken to use distilled water and to see that the materials are pure and that all apparatus used is clean. If there is any doubt as to the purity of the materials, a blank test should be made. To do this proceed just as directed above, except that the sample of soil is omitted. EXERCISE 85 ACTION OF HARD WATERS ON SOAP (OPTIONAL) Apparatus. Two 2^o-cc. bottles; burette or graduated cylinder; 2 test tubes. Materials, i g. soap dissolved in 100 cc. distilled water ; samples of hard water (100 cc.); samples of one or more washing-powders. 1. The determination of the amount of soap lost by using hard water for washing. Place two 2 50-00. bottles on the desk. Into the first pour 100 cc. of hard water (preferably an average [133] FIG. 85. Testing soils by the Truog method sample of the water used in your town or city) and into the second pour 100 cc. of distilled (or rain) water. Now add to each the soap solution, i cc. at a time, and shake the bottle vigorously after each addition. Continue adding the soap solu- tion until the lather formed on shaking the mixture persists for five minutes, (a) Compare the amounts of the soap solu- tion required in each case to produce a permanent lather. The difference in the amounts represents the soap consumed by using the hard water in place of soft water. It will be interesting to make a rough approximation of the amount of hard water used yearly in your city for washing, and then to determine approximately the cost of the soap lost in one year owing to the use of hard water. 2. The analysis of washing-powders. Devise methods for detecting the presence of the following substances, if present in washing-powders: (b) sodium carbonate; (c) borax (Exer- cise 72); (d) mineral matter, such as sand. Submit your methods to your instructor for criticism ; then test one or more washing-powders for these substances, (e) Record your results. EXERCISE 86 MAGNESIUM AND ITS COMPOUNDS Apparatus. Porcelain crucible and cover; small beaker; pipestem triangle; evaporating-dish ; forceps. Materials. Strips of magnesium 5 cm. long ; blue and red litmus papers ; 2 to 3 g. magnesium carbonate ; hydrochloric acid. 1. Wind a strip of magnesium wire into a coil and place it in a porcelain crucible. Put the cover on the crucible and apply a gentle heat. By means of your forceps raise the cover slightly from time to time so as to admit air. Continue until the mag- nesium is entirely burned, leaving a white powder, (a) What is the composition of the powder? Add the powder to 25 cc. of water. Stir the mixture and test it with litmus paper. (b) Account for the results. [1341 2. Convert 2 or 3 g. of magnesium carbonate into the chloride. (c) Describe the process. Evaporate the solution of the chlo- ride to complete dryness in an evaporating-dish, heating the residue gently with the bare flame. When it is cool add a few drops of water, stir, and test with litmus, (d) Account for the results, (e) Why are waters containing magnesium chloride objectionable for use in steam boilers? (Consult text.) EXERCISE 87 ZINC AND ITS COMPOUNDS Apparatus. Blowpipe and charcoal (Fig. 86); 3 test tubes; beaker. Materials. 0.5 g. zinc; sulfuric acid; sodium hydroxide solution; ammonium sulfide (R.S.); i g. zinc sulfate. 1. Place a bit of zinc on charcoal and heat it in the oxidizing flame produced by a blowpipe (Fig. 86). The resulting oxide is deposited as a film on the char- coal, (a) Note its color, (b) Is its color the same when hot as when cold? (c) For what is this oxide used? 2. Dissolve o.5g. of zinc sulfate in 10 cc. of water. Divide this solu- tion into 2 parts and test with the following re- FIG. 86. Heating a metal in the oxidizing flame agents: (i) sodium hydroxide solution (i drop, or just sufficient to cause a precipitate) ; zinc hydroxide precipitates ((d) write the equation for its formation), but the precipitate dissolves [1351 again if an excess of sodium hydroxide is added; (2) am- monium sulfide; zinc sulfide precipitates, (e) Write the equa- tion for the reaction involved. (/) What is the color of zinc sulfide? 3. Perform experiment i, Exercise 88, so that the exercise may be concluded at your next laboratory period. EXERCISE 88 RUBBER Apparatus. 2 beakers (loo-cc. and 300-00.); test tube; stirring-rod; glass plate for covering bottles. Materials. 1.5 g. natural rubber; 35 cc. carbon tetrachloride ; 0.2 g. flowers of sulfur or finely powdered brimstone; acetic acid (R.S.); filter paper. 1. Put about i g. of natural rubber in a loo-cc. beaker and pour over it 25cc. of carbon tetrachloride. Place over the top of the beaker a filter paper, and on this a glass plate so as to prevent the liquid from evapo- rating. Set the beaker aside until the next laboratory period. Also intro- duce about o.i g. of natural rubber into a test tube and pour over it suffi- cient carbon tetrachloride to half fill the tube ; then cork the tube and set it aside until the next laboratory period (if opportunity is afforded, it is well to stir the mixtures once or twice before the next period ) . In both cases the rubber forms a colloid gel in the carbon tetrachloride. 2. Stir the mixture in the beaker thoroughly; then add to it about 0.2 g. flowers of sulfur and stir the sulfur until it is uniformly distributed through the mass. Pour into a large [136] FIG. 87. Evaporating a liquid by placing the beaker contain- ing the liquid inside a larger beaker partially filled with boiling water beaker sufficient water so that the smaller beaker containing the rubber will float on the water, as shown in Fig. 87. Heat the water to boiling and maintain the boiling for half an hour or more, until the carbon tetrachloride in the small beaker is all evaporated and the rubber forms a film closely adhering to the sides of the beaker. Then remove the small beaker, and by means of a knife blade peel off the adhering rubber. (a) Compare the resulting rubber in properties with the natural rubber. 3. Shake the test tube containing the colloid rubber vigor- ously so as to form a uniform mass; then add 2 or 3 cc. of acetic acid and again shake the tube. Set the tube aside for a few minutes, (b) Does the colloid (rubber) settle? (c) What is the action of the acetic acid? (Consult chapter on colloids in text.) EXERCISE 89 ALUMINIUM AND ITS COMPOUNDS Apparatus. 2 test tubes; blowpipe and charcoal; 2 beakers; funnel. Materials. 2 g. aluminium turnings ; sodium hydroxide solution ; wooden splint ; hydrochloric acid ; ammonium hydroxide ; filter paper ; aluminium sulfate solution (R. S.) ; 2 or 3 drops of cobalt nitrate solu- tion (R. S.) ; i g. sodium carbonate in 5 cc. water; (aluminium sulfate and potassium sulfate sufficient to make 20 g. of crystals of potassium alum). 1. (a) Note the physical properties of aluminium. Introduce about 0.5 g. of aluminium into a test tube and pour over it 2 cc. of sodium hydroxide solution. Heat the mixture gently. (b) What evidence have you that the aluminium is acted upon by the hydroxide? (c) Close the mouth of the tube for a few seconds with your thumb ; then remove it and at once test the gas with a lighted splint, (d) What is the gas? (e) What would be the effect of washing aluminium cooking vessels with lye or strong soap ? 2. Introduce about i g. of aluminium into a test tube, add 5 cc. of water and then hydrochloric acid, a drop at a time, [137] sufficient to dissolve the metal. Filter (if necessary) and dilute the solution to about 50 cc. To this add ammonium hydroxide until the solution reacts alkaline. .(/) Note the results and write the equation for the reactions involved. 3. Filter off some of the aluminium hydroxide prepared in i and heat it on charcoal in the oxidizing flame of the blowpipe (Fig. 86). The aluminium hydroxide is decomposed into alu- minium oxide and water, (g) Write the equation for the re- action. Now moisten the residue on the charcoal with one or two drops of a solution of cobalt nitrate and again heat strongly in the blowpipe flame, (h) Note the change in color. Ad- vantage is sometimes taken of this property in testing for the presence of aluminium. 4. Add a solution of sodium carbonate to any aluminium salt such as aluminium sulfate. Note that a gas is evolved. (i) Devise a method for determining whether or not this gas is carbon dioxide and make the test. (;) Advantage is taken of this reaction in the preparation of what culinary product ? 5. Calculate the weights of aluminium sulfate (the crystals of alu- minium sulfate have the formula A1 2 (S0 4 ) 3 16 H 2 0) and of potassium sulfate required to prepare 20 g. of crystals of potassium alum; then dis- solve these amounts of the two compounds separately in as little water as possible, mix the two solutions thoroughly, and set the resulting solu- tion aside for a few days to crystallize. If a string is suspended in the liquid, the crystals will deposit on it. These may then be withdrawn and their properties studied, (k) Note the shape of the crystals. EXERCISE 90 A STUDY OF THE USE OF ALUMINIUM SULFATE IN THE PURIFICATION OF WATER Apparatus. Three 25o-cc. wide-mouthed bottles ; graduated tube. Materials. Aluminium sulfate solution (R. S.) ; limewater (R.S.). 1. Label three 25o-cc. wide-mouthed bottles A, B, and C respectively. Nearly fill A and B with muddy water, pouring a like volume of distilled water into C. Add 5 drops of alu- [ 138] minium sulfate solution to A and C respectively. Mix the con- tents of each bottle thoroughly. Now to each of the bottles A and C add 10 cc. of limewater. Set the bottles aside and examine at the beginning of the next laboratory period. (a) Record the results and explain the reactions. What is the use of bottle B ? EXERCISE 91 REACTIONS OF BAKING-POWDERS Apparatus. 250-00. flask to fit; stirring-rod; mortar and pestle. Materials. 4 g. sodium bicarbonate ; limewater (R. S.) ; alum ; cream of tartar. 1. By referring to the equations for the reactions of different classes of baking-powders as given in your text, calculate and (a) record the weight of ammonium alum (NH 4 A1(SO 4 ) 2 i2H O) necessary to react with 2 g. of sodium bicarbonate; then grind together these weights of alum and bicarbonate so as to mix them thoroughly. Put the mixture into a 250-0:. flask and cover the mixture with water. Gently rotate the flask so as to form a uniform mixture, at the same time heating the mixture slightly ; then set the flask aside for five minutes. Now test for the presence of carbon dioxide in the air in the flask (Fig. 54). (b) Note and explain the results. 2. Repeat i, substituting cream of tartar for the alum. (c) Record your results. 3. (d) What compounds remain in food as a result of the use of an alum baking-powder; (e) of a cream-of -tartar baking- powder ? 139] EXERCISE 92 ANALYSIS OF BAKING-POWDERS (OPTIONAL) Apparatus. 2 small beakers ; stirring-rod ; funnel ; evaporating-dish ; 5 test tubes. Materials. 10 g. each of various kinds of baking-powders ; iodine solution (R.S.); filter paper; barium chloride solution (R.S.); hydro- chloric acid; sulfuric acid; nitric acid; ammonium molybdate solution (R.S.) ; sodium hydroxide. 1. Introduce 10 g. of a baking-powder into a beaker and pour over it 50 cc. of water. Stir the mixture thoroughly until no more gas is evolved, then filter it, and test the residue and the filtrate for the various ingredients, as explained below. 2. Starch, (a) Will any starch present be in the residue or in the filtrate? Make appropriate test, (b) Record the test used and the results obtained. 3. Sulfates. (c) All alums are salts of what acid? (d) Make appropriate test for these salts, giving the method and the results. 4. Tartrates. Pour 5 cc. of the filtrate into an evaporating- dish, add 5 drops of sulfuric acid, and evaporate to dryness. Finally, heat the dish gently with a bare flame. The presence of a tartrate is indicated by an odor similar to that of burning sugar, (e) Record the results of your test of different powders. 5. Ammonium salts. Ammonium alum is sometimes used in baking-powders. To detect this, pour 5 cc. of the filtrate into a test tube, add an equal volume of sodium hydroxide solution, and heat gently. If ammonium salts are present, ammonia will be evolved (Exercise 78). 6. Phosphates. If calcium or sodium phosphate is present in the baking-powder, the filtrate will contain the acid phosphate of the metal. To detect phosphates, treat 5 cc. of the filtrate with a few drops of nitric acid, heat nearly to boiling, and add a [140] few drops of the mixture to 5 cc. of ammonium molybdate solu- tion (compare Exercise 67). (/) Record the results obtained. 7. Aluminium, calcium, sodium, and potassium. A baking- powder containing sulfates always contains aluminium, while one containing phosphates always contains calcium or sodium ; cream-of-tartar baking-powders, on the other hand, always contain potassium. The presence or absence of these metals may be inferred from the tests made for sulfates, phosphates, and cream of tartar. EXERCISE 93 THE USE OF MORDANTS IN DYEING (OPTIONAL) Apparatus. 200-cc. beaker; stirring-rod; large beaker. Materials. 2 strips (2 cm. x 6 cm.) of white woolen cloth (nun's veiling serves well) ; 6 strips of white cotton cloth ; i g. sodium car- bonate in 50 cc. water ; 0.5 g. tannic acid in 50 cc. water ; 0.2 g. tartar- emetic in 50 cc. water; o.ig. of any of the following dyes in 1500:. water (different students should select different dyes and compare re- sults) : fuchsine, methyl violet, gallein, malachite green, Congo red; (a solution containing i g. sodium carbonate, 5 g. Glauber's salt, and o.i g. Congo red in 50 cc. water). 1. Most dyes will dye animal fibers (wool, silk) directly, but will dye vegetable fibers (cotton, linen) fast only when mordants are used. Place the strips of cotton cloth in a beaker and cover them with the sodium carbonate solution ( i g. in 50 cc. of water) and boil the liquid for five minutes. Remove the strips and thoroughly rinse them with water. This treatment serves to remove all foreign matter from the cloth. Now completely immerse two strips of the cotton cloth in the tannic-acid solution, heat until it is fairly warm to the hand (50 or 60), and maintain the temperature for ten minutes. Remove the cloth from the solution and squeeze out the liquid, but do not rinse the cloth; then immerse the strips for one minute in the slightly warmed solution of tartar-emetic. The [141] tannic acid in the cloth reacts with the tartar-emetic, forming a salt (known as antimonyl tannate) which becomes incor- porated in the meshes of the fiber and serves as a mordant. Remove the cloth from the solution and rinse it. Divide the solution of the dye chosen into three equal por- tions. Heat one portion in a small beaker just to boiling, im- merse a strip of woolen cloth, and continue the heating for about five minutes. Be sure to keep the cloth entirely im- mersed in the dye, using the glass stirring-rod for this purpose. Now remove the cloth and rinse it thoroughly. To test whether the cloth is dyed fast, rinse it thoroughly and then wash it in a beaker of water and note whether the water becomes colored. In a similar way dye a strip of unmordanted cotton cloth in the second portion of the dye and a strip of mordanted cloth in the third portion, and determine in each case whether the cloth is dyed fast, (a) Finally, dry the three strips of cloth and in- sert them in your notebook and record the results of your experiments. 2. Some dyes (known as substantive dyes) have the property of dyeing cotton fast without the use of mordants. The ordinary dyes sold by druggists belong to this class. Congo red is a typical dye of this class. Heat the solution of Congo red, prepared as directed under "Mate- rials," to boiling, immerse in it a strip of wet unmordanted cotton, and continue the boiling for five minutes. Remove the cloth, rinse, and test to see whether the cloth is dyed fast. Dry the strip and insert it in your notebook. (The sodium carbonate and the sodium sulfate assist in the process, but do not act as mordants.) (Save the remaining strips of cotton for use in Exercise 94.) [142] EXERCISE 94 A STUDY OF LAKES; ALSO THE EFFECT OF USING DIF- FERENT MORDANTS WITH THE SAME DYE (OPTIONAL) Apparatus. Two 250-00. wide-mouthed bottles; evaporating-dish ; 2 small beakers; stirring-rods. Materials. 5 cc. of a 2o-per-cent solution of alizarin paste; o.i g. of gallein dissolved in 50 cc. water ; solutions of aluminium sulfate and ferric sulfate (R. S.); ammonium hydroxide; 3 strips of cotton cloth prepared in Exercise 93. 1. Formation of lakes. Label two wide-mouthed bottles A and B respectively. Shake the alizarin paste so as to form a uniform mixture; then introduce about 10 drops of the paste into each of the bottles. Next add to each of the bottles 2 cc. of ammonium hydroxide and then 200 cc. of water, and mix the contents thoroughly. Now add 10 cc. of aluminium sulfate solution to bottle A and 10 cc. of ferric sulfate to bottle B, intimately mix the solutions, and set the bottles aside; (a) note the appearance of the contents at the end of the laboratory period, also at the beginning of the next laboratory period. (b) What is the function of each of the materials used? 2. Mordanting strips of cloth with aluminium hydroxide or ferric hydroxide. Pour about 20 cc. of aluminium sulfate solu- tion or ferric sulfate solution into a small beaker and heat to boiling (different students should use different solutions and compare results). Completely immerse in this solution two of the strips of cotton cloth prepared in Exercise 93, and continue the heating for from two to three minutes. Remove the cloth, squeeze it between the fingers to remove the excess of the solution, and immerse it in 20 cc. of water containing from i to 2 cc. of ammonium hydroxide. Warm the liquid slightly for two minutes, then remove the cloth and rinse it twice in water, (c) What compound is now incorporated in the cloth? f 1431 3. Dyeing a strip of mordanted cloth with alizarin. Pour i cc. of alizarin paste into a small beaker, add 20 cc. of water, stir, and heat to boiling. Completely immerse one of the strips of mordanted cloth prepared in 2 and continue the heating and stirring for five minutes; then 'remove the cloth and rinse thoroughly. Dry the dyed strip and insert it in your notebook. 4. Dyeing a strip of mordanted cloth with gallein. Heat the solution of gallein just to boiling ; then immerse one of the mordanted strips of cotton in the dye. Keep the strip com- pletely immersed in the dye, and continue the heating for five minutes; then remove the cloth and rinse it. Dry the dyed strip and insert it in your notebook. EXERCISE 95 THE DETECTION OF DYES IN FOODS (OPTIONAL) Apparatus. Small beaker; stirring-rod. Materials. Samples of colored pop and orangeade ; strips of woolen cloth (nun's veiling gives good results) ; hydrochloric acid. 1. Select different samples of colored pop. Pour 50 cc. of each into a beaker, add 2 or 3 drops of hydrochloric acid, and heat to boiling ; then introduce a strip of woolen cloth and continue the heating for -five minutes. Be careful to keep the cloth completely immersed in the liquid, (a) Remove the cloth, rinse, and note the color. 2. Samples of colored candies may be tested by first dissolv- ing the candy in water and then testing the solution for dyes by using strips of woolen cloth, as in the above case. Tomato catchup is sometimes colored, although the practice is for- bidden by Federal law. To test a catchup for dyes, heat a portion of the catchup diluted with water and immerse a strip of woolen cloth in the hot mixture for five minutes. Remove the cloth and rinse thoroughly. If artificial dyes are present, the cloth will be deeply colored; otherwise it will have only a slight brownish tinge produced by the natural coloring- matter of the tomato. [144] EXERCISE 96 CLAY; PORTLAND CEMENT; MORTAR Apparatus. Evaporating-dish ; 2 beakers ; a piece of wooden shingle or board about as large as the palm of your hand ; ordinary kitchen knife. Materials. Small samples (half a cupful) of samples of different clays; 30 g. Portland cement; 15 g. sand; 15 g. lime (this should be taken from a lump of lime freshly made); 2 small pasteboard boxes (pill boxes will do). 1. Add water, a little at a time, to different samples of clay and work it intimately through the clay until a thick, plastic mass is obtained. Devise a rough method for testing the relative plasticity of different clays in a general way and apply it to the clays at hand, arranging them in the order of their plas- ticity, (a) Describe the method you used. 2. To 25 or 30 g. of Portland cement add water, a little at a time, and stir it through the mass until a thick paste is obtained. Spread a portion of this on a shingle and set it aside until the next laboratory period. With the remainder fill a small paper pill box. Place the box in a beaker half full of water. Set the beaker and contents aside until the next period, (b) Ex- amine the cement placed on the board, also that in the beaker, and note whether the samples have hardened, or "set." 3. Repeat experiment 2, using, in place of the cement, some mortar made as follows: Add to 15 g. of lime 10 cc. of water. The lime will "slake" and form a thin paste with the excess of water. Now work through this, a little at a time, 15 g. of fine sand, adding more water if necessary, to keep the mortar from becoming too thick. Place some of this on a shingle and with the rest fill a paper pill box; then proceed as in experiment 2. (c) Describe the results obtained, noting in particular any difference in the properties of Portland cement and mortar. [145] EXERCISE 97 A STUDY OF IRON AND ITS COMPOUNDS Apparatus. Forceps; 2 beakers; watch glass; funnel; (flask (25o-cc.); 8 test tubes). Materials. Watch spring from 10 to 15 cm. in length (broken watch springs can be obtained from any jeweler) ; 5 g. small tacks or fine iron wire; 0,5 g. powdered iron; filter paper; sulfuric acid; (nitric acid; hydrochloric acid ; ammonium hydroxide ; potassium ferrocyanide (R.S.); potassium sulfocyanate (R.S.)). 1. The tempering of steel. Heat a piece of watch spring (from 10 to 15 cm. in length) to a white heat in a Bunsen flame. Let it cool slowly, and when cold bend it to determine if it is brittle. Again heat to a white heat and at once plunge into a beaker of cold water. When cool, bend the piece as before. Reheat the piece, allow it to cool slowly, and again examine it. (a) Record the results of the experiments. 2. Preparation of ferrous sulfate (copperas). Place 5 g. of fine iron wire or small tacks in a beaker and pour over it 15 cc. of water. Now add (care) 4 cc. of concentrated sulfuric acid and heat very gently (hood) until a vigorous evolution of gas takes place ; then cover the beaker with a watch glass and set it aside in the hood until near the end of the laboratory period. Then add 10 cc. of water, and heat slowly until the liquid boils, stirring the mixture constantly. Filter off any undissolved solids, collecting the nitrate in a beaker. Set the uncovered beaker containing the filtrate in your desk until the next laboratory period, (b) Record the properties of the crystals. (c) Write the equation for their formation from iron. 3. Preparation of ferrous and ferric salts and their reactions. Place about 0.5 g. of iron powder in a small flask and pour over it 5 cc. of water and then 2 cc. of hydrochloric acid. Mix the contents of the flask, heat the flask gently, and set it aside in the hood for about five minutes. The iron dissolves in the hydrochloric acid, forming ferrous r 1461 chloride. Now add 50 cc. of water to the flask, mix well, and filter off the undissolved iron. Nearly fill a test tube with the filtrate, add to it 4 or 5 drops of hydrochloric acid and a small piece of iron wire or i or 2 tacks, and loosely cork the tube. Mark this "Solution A." It consists of a solution of ferrous chloride. The iron wire and the hydrochloric acid generate a little hydrogen, which prevents the oxidation of the ferrous chloride to ferric chloride by the oxygen of the air. Mark the remainder of the filtrate "Solution B." To Solution B add i cc. of hydrochloric acid and heat it nearly to boiling; then withdraw the flame and add nitric acid, drop by drop, with constant stirring, until the solution, which is at first dark brown in color, becomes light in color (about 2 cc. of nitric acid will be required) The ferrous chloride in the solution is changed to ferric chloride by the oxygen furnished by the nitric acid, thus : 2 FeCl 2 + 2 HC1 + 2 FeCl H 2 Now compare the action of the following reagents upon Solutions A and B (add 2 or 3 drops of the reagents to 3 cc. of the solutions in separate test tubes) : ammonium hydroxide, potassium ferrocyanide, potassium sulfocyanate (KCNS). Tabulate your results as follows : FERROUS CHLORIDE (Solution A) FERRIC CHLORIDE (Solution B) Ammonium hydroxide Potassium ferrocyanide .... Potassium sulfocyanate .... EXERCISE 98 THE REMOVAL OF STAINS Apparatus. 4 test tubes; 2 beakers; evaporating-dish. Materials. 0.2 g. tannic acid dissolved in 10 cc. water ; ferric sulfate (R. S.) ; 2 pieces of white cloth 10 cm. square ; i g. oxalic acid dissolved in 50 cc. water ; hydrochloric acid ; 2 strips of black cloth 5 cm. square ; nitric acid ; ammonium hydroxide ; a few drops each of cottonseed oil and sirup (molasses) ; 25 cc. carbon tetrachloride ; blotting-paper; strips of cloth stained witH coffee and fruit juice ; acetic acid (R. S.) ; 20 g. bleaching-powder ; hot water. 1. Stain two strips of white cloth by dipping them into a solu- tion of ferric sulfate until thoroughly saturated and then into [147] a solution of tannic acid (or they may be stained directly with black ink). Wash one of the strips repeatedly with boiling water. Leave the other exposed to the air until dry ; then try the effect of hot water upon the stain. If the stain is not re- moved, wash with a dilute solution of oxalic acid and finally with hot water, (a) Record your results. 2. Place 2 or 3 drops of dilute hydrochloric acid upon a strip of black cloth, (b) What color is produced? Wash the spots with 10 cc. of water containing 4 or 5 drops of ammonium hydroxide, (c) Do the spots disappear? Repeat, using nitric acid in place of hydrochloric acid, (d) Account for the results. 3. Place in separate test tubes 4 or 5 drops of a sirup and a like amount of fat, such as cottonseed oil. Test the solubilities of each in water and in carbon tetrachloride. (e) Suggest a method for removing stains made by sirups and one for those made by fats. Stain some strips of cloth with sirup and with an oil and test your methods for removing these stains. (In applying a solvent it is convenient to place the stained portion of the cloth over a piece of blotting-paper. A small bit of sponge or cloth, saturated with the solvent, is then rubbed about the stained portion, gradually nearing the stain itself, which is finally thoroughly rubbed.) Benzine (or gasoline) may be used in place of the carbon tetrachloride. // benzine is used, however, it must be remem- bered that it is very inflammable. Never use it in the vicinity of a flame. 4. Stain some strips of cloth with coffee and with fruit juices. (/) Are the stains removed by washing with boiling water? If the stain cannot be removed in this way, wash the stained portion of the cloth in bleaching-powder to which has been added some water and 3 or 4 drops of acetic acid. 148 EXERCISE 99 A STUDY OF COPPER AND ITS COMPOUNDS Apparatus. 3 test tubes ; beaker ; (porcelain crucible ; pipestem tri- angle; balance). Materials. Nail ; copper sulfate solution (R. S.) ; sodium hydroxide ; ammonium hydroxide ; 10 cm. copper wire ; hydrochloric acid ; (3 g. copper sulfate crystals). 1. (a) Recall the action of nitric acid and of sulfuric acid on copper (Exercises 37, 43) ; also the action of sulfur on copper (Exercise 40). Suspend an iron nail so that half its length is immersed in a solution of copper sulfate for five minutes. (b) Account for the result. 2. To 2 cc. of a cold solution of copper sulfate in a test tube add one half its volume of sodium hydroxide solution. Copper hydroxide, Cu(OH) , is precipitated. Now heat to boiling. The hydroxide is decomposed into water and cupric oxide (black), (c) Write the equations for the reactions. 3. Add i drop of ammonium hydroxide to a dilute solution of copper sulfate ; now continue to add the ammonium hydrox- ide, drop by drop, until the precipitate which is at first formed is dissolved, (d) How does the color of this solution compare with that of the original solution? This reaction is charac- teristic of copper compounds. 4. (e) Recall the formation of cuprous oxide (Exercise 55). 5. Moisten the end of a copper wire with hydrochloric acid and hold it in the edge of a Bunsen flame. (/) What is the color of the flame? (g) What is the function of the acid? 6. The determination of the percentage of water of hydration in copper sulfate (quantitative). Accurately weigh (or counterpoise) a porcelain crucible and cover. Record all weights in the table below. Place 2 or 3 g. of crystals (no larger than a pea) of copper sulfate in the crucible and again accurately weigh. Place the covered crucible on a pipestem triangle and heat it with a gentle flame until the crystals lose [149] their color. This will require from twenty to thirty minutes. The tip of the flame should not quite touch the crucible. The product is an- hydrous copper sulfate. When the crucible is cool, reweigh. From your results calculate the percentage of water of crystallization in the crys- tals. Fill in the blank spaces in the table below : Weight of crucible g. Weight of crucible plus copper sulfate crystals ... g. Weight of copper sulfate (calculate) g. Weight of crucible plus anhydrous copper sulfate . . g. Weight of anhydrous copper sulfate g. Weight of water of hydration (calculate) .... g. Percentage of water of hydration in crystals ... % Theoretical percentage of water of hydration ... % Average of results obtained by members of the class . % EXERCISE 100 A STUDY OF MERCURY AND ITS COMPOUNDS Apparatus. loo-cc. beaker; 2 test tubes. Materials. Globule of mercury (size of a grain of wheat) ; nitric add ; copper penny ; 0.5 g. mercuric oxide ; 3 cc. solution of mercurous nitrate (R. S.); hydrochloric acid. 1. (a) Note the physical properties of mercury. Place a globule of it in a small beaker and add (hood) just enough nitric acid to dissolve it. Dilute the product with 10 cc. of water and place a copper penny in the solution. After a few minutes remove the coin and polish it with a piece of cloth. (b) Account for the result (recall the displacement series of the metals). 2. For what purpose have we used mercuric oxide? Place 0.5 g. of it in a test tube and dissolve it in as little nitric acid as possible, (c) What compound of mercury is formed? Then add water until the test tube is one fourth full. Into a second test tube pour a similar volume of a solution of mercurous nitrate. Now add 2 or 3 drops of hydrochloric acid to each test tube, (d) What conclusions do you draw in reference to the solubility of the two chlorides of mercury? [ISO] EXERCISE 101 A STUDY OF SILVER AND ITS COMPOUNDS Apparatus. 2Oo-cc. beaker; stirring-rod; funnel; blowpipe and piece of charcoal; 3 test tubes. Materials. Silver dime; nitric acid; hydrochloric acid; ammonium hydroxide ; filter paper ; hot water ; 2 or 3 g. sodium carbonate ; 10 cc. silver nitrate solution (R. S.) ; solutions of potassium bromide and of potassium iodide (R. S.). 1. Place a silver dime in a small beaker and add (hood) suf- ficient nitric acid to dissolve it. The solution may be hastened by applying a gentle heat. When the solution is complete, dilute the product with about 25 cc. of water, (a) Account for the color of the liquid. Now add, drop by drop, with con- stant stirring, a solution of hydrochloric acid. The precipitate formed settles to the bottom of the beaker when stirred. Con- tinue adding the acid until a drop of the acid no longer causes a precipitate when it comes in contact with the clear liquid in the beaker. Now carefully pour off the clear liquid from the precipitate and add ammonium hydroxide to this liquid until the solution becomes alkaline, (b) Account for the change in color (3, Exercise 99). Wash the precipitate remaining in the beaker two or three times by pouring hot water over it and decanting. Finally, remove any remaining water by filtration. Mix the product with an equal bulk of sodium carbonate, transfer to a small cavity in a piece of charcoal, and heat it in the blowpipe flame. The silver salt is gradually reduced to metallic silver, which will fuse into a globule if sufficient heat is applied, (c) How does the product differ in composition from that of the original coin ? 2. Prepare small amounts of the chloride, the bromide, and the iodide of silver. (G?) Give the methods you employed. Ex- pose to the sunlight the test tubes containing the precipitates and note any changes. For what are these compounds used ? F1511 EXERCISE 102 THE CHEMISTRY OF PHOTOGRAPHY Apparatus. 4 test tubes; hard-glass test tube; 5oo-cc. beaker; glass rod ; piece of window glass. Materials. Solution of potassium bromide (R.S.); solution of silver nitrate (R.S.); 0.5 g. silver nitrate; 0.5 g. potassium bromide; 3 g. powdered gelatin; tube of any commercial photographic developer; solution of sodium thiosulfate (R.S.). 1. Preparation of the plate or film. Pour into a test tube 3 cc. of a solution of potassium bromide and add to this 2 cc. of a solution of silver nitrate, (a) What is the compound formed? Place the tube and contents in the bright sunlight for two or three min- utes, (b) Do you observe any change in color? It is not possible to coat a glass plate or film with the pure silver bromide. The bromide is therefore suspended in a finely divided state in an emulsion of gelatin, and the glass coated with the emulsion. The gelatin keeps the bro- mide in a finely divided state and also makes it much more sensitive to light. Proceed as follows: Half fill a 500-cc. beaker with water, heat until the water is uncomfortably hot to your finger, and maintain this temperature with a small flame. Now pour 3 cc. of water into a test tube and add to it 0.5 g. of silver nitrate. Shake the mixture until the nitrate is dissolved ; then place the tube in the beaker, as shown in Fig. 88. Next pour 3 cc. of water in your hard-glass test tube (used in preparing oxygen), and place [1521 FIG. 88. Heating a liquid in a test tube by immersing the tube in hot water this in the hot water in the beaker until the water in the tube has about the same temperature as that in the beaker* Next add to the tube 0.5 g. of potassium bromide and then, a little at a time, with constant stirring (use a glass rod), from 2 to 3 g. of powdered gelatin. When the gelatin is uniformly dis- tributed through the hot water, add to this, a little at a time, the hot solution of silver nitrate from the tube in the beaker, stirring it thoroughly with a glass rod. The hot emulsion gradually becomes thinner. Now pour this emulsion (keep it away from a bright light) onto a glass plate, tilting the plate until the emulsion forms a uniform coating on the plate. Set this aside for five or ten minutes until the emulsion hardens. In actual practice all these operations must be carried out in a dark room, (c) What is the composition of the emulsion? (d) Note its color. Now expose the plate to the bright sun- light for a few minutes, (e) Note the change in color. 2. The chemistry of the development of image. Pour into a test tube 2 cc. of a silver nitrate solution and add to this 3 cc. of potassium bromide solution. Do not shake the tube, as this will cause the precipitate to form a compact mass. (/) Record your results. Expose the tube and contents to the bright light for five or ten seconds ; then add to it 5 cc. of a solution of the developer prepared as directed in the instructions accompany- ing the developer, (g) Record and explain the results. Save the tube and contents for experiment 3. 3. The chemistry of "fixing" the negatives. Pour off the liquid from the tube (experiment 2), leaving the solid in the tube, and add to this solid 10 cc. of a solution of sodium thio- sulfate (hypo). Shake the mixture vigorously for about one minute, (h) Does the precipitate dissolve? Set the tube aside for comparison later. 4. Now repeat experiments 2 and 3 in a dark room (omitting, of course, the exposure to light, as directed in experiment 2). (i) Account for the difference in the results obtained when the experiment is performed in the absence of light. (If a dark [153] room is not available, fairly acceptable results may be obtained by wrapping a piece of black paper around the tube in which the reactions are carried out and performing the experiment in a dark place in the laboratory.) EXERCISE 103 SOME PROPERTIES OF TIN Apparatus. loo-cc. beaker; blowpipe and charcoal. Materials. 2 g. tin; hydrochloric acid; solution of mercuric chloride (R..S.). 1. (a) Note the physical properties of tin. (jb) Heat a bit of it on charcoal (Fig. 86) and note the changes. 2. Dissolve about i g. of the metal in hydrochloric acid. (c) What is formed? Cool, dilute with a little water, and add i to 2 drops of the solution to 3 cc. of mercuric chloride solution. A white precipitate of mercurous chloride forms : SnCl 2 + 2 HgCl 2 >- SnCl 4 + 2 HgCl Now add a few drops more of the stannous chloride solution and heat the mixture gently. The mercurous chloride is reduced to metallic mercury, which forms a dark-gray precipitate: SnCl 2 + 2 HgCl >- SnCl 4 + 2 Hg EXERCISE 104 A STUDY OF LEAD AND SOME OF ITS COMPOUNDS Apparatus. Blowpipe and charcoal ; 5 test tubes. Materials. 2 g. lead (obtain some scrap lead from a plumber) ; lead acetate (R.S.); 0.5 g. lead nitrate dissolved in 5 cc. water; ammo- nium sulfide (R.S.); sulfuric acid; potassium chromate (R.S.); hydro- chloric acid ; piece of mossy zinc ; thread or string about 50 cm. long ; 10 cc. hydrogen peroxide. 1. (a) Note the physical properties of the metal. Heat a small bit on charcoal, (b) Is it easily melted? (c) Account for the coating formed on the charcoal. [ 1541 2. To a piece of mossy zinc about as large as the end of your finger tie a piece of thread and suspend the zinc about the middle of a test tube which is nearly filled with a solution of lead acetate. Set the tube aside until the end of the laboratory period, noting, every few minutes, any changes taking place. Leave the tube and contents until the next laboratory period and again note the changes, (d) Describe the results and the chemistry involved. 3. Pour i cc. of the solution of lead nitrate into a test tube and add one drop of ammonium sulfide. Black lead sulfide is formed, (e) Write the equation for the reaction. Now add to the mixture 7 or 8 cc. of hydrogen peroxide solution, shake the mixture, and set it aside for ten minutes. (/) Account for the change in color (recall that hydrogen peroxide is a good oxi- dizing agent). 4. To the remainder of the lead nitrate solution add 2 or 3 drops of potassium chromate solution. Yellow lead chromate (PbCrO 4 ) is formed. This is used as a pigment under the name of chrome yellow. Pb(NO 3 ) 2 + K 2 CrO 4 >- PbCrO 4 + 2 KNO 3 EXERCISE 105 SIMPLE CELLS FOR PRODUCING ELECTRIC CURRENTS Apparatus. Beaker (ioo-cc.); screw clamp. Materials, i strip each of sheet iron and of zinc about i cm. x 10 cm. 50 cc. water, to which is added i cc. sulfuric acid. 1. Action of metals in a cell (for producing an electric cur- rent). A cell in its simplest form consists of two strips of different metals joined together at one end by a wire while the other ends are immersed in a dilute solution of an acid, such as sulfuric. One of the strips will slowly dissolve in the acid while hydrogen escapes from the surface of the other metal. As a result of the action an electric current is generated and flows [ 1551 through the wire. To determine which of the metals is dis- solved, proceed as follows : Cut a strip of sheet iron about 10 cm. x i cm. ; also a similar strip of zinc. Polish one end of each strip so as to remove all foreign matter and then clamp the ends firmly together by a screw clamp. Bend the two strips in the form of the letter V and immerse the disconnected ends in a solution of sulfuric acid (made by adding i cc. of the acid to 50 cc. of water), as shown in Fig. 89. (a) Note from which metal hydro- gen escapes (if the metals are impure, hy- drogen may escape from both metals, but the amount escaping from one of the metals will always be in excess). Set the beaker and metals aside for one or two hours (or until the next period), (b) Note which of the metals has been dissolved, (c) Note the relative positions of zinc and iron in the displacement series. When any two metals are connected, as in the above experi- ment, the one nearest the top of the displacement series is always the one which is dissolved. 2. Galvanized iron consists of strips of iron coated with zinc. If the zinc is worn away at any point so as to expose the iron, and moisture is present, a local current will set up. (d) Which of the two metals will be dissolved? (e) What is the composition of tin plate? (/) If the outside metal is worn away, and moisture is present, which of the two metals will be dissolved ? FIG. 89. A simple cell for producing an elec- tric current [156] EXERCISE 106 PAINTS Apparatus. Blowpipe and charcoal; test tube; funnel and filter paper ; small beaker. Materials. About 5 g. of samples of white paints; 5 cc. carbon tetrachloride; i cc. ammonium sulfide (R. S.); filter paper; splint. 1. Introduce 2 or 3 g. of a sample of a white paint into a test tube and then add carbon tetrachloride until the tube is about one fourth full. Shake the tube and contents vigorously ; then set it aside for a few minutes (or until you have performed the experiments below), (a) Does the solid matter in the paint settle to the bottom of the tube? Shake the tube again, and filter, (b) Is the filtrate clear? (c) In what form is the solid matter present in the paint? (d) What constituent of paint is soluble in carbon tetrachloride? Place 2 or 3 drops of the filtrate on a piece of filter paper and put it aside until the car- bon tetrachloride evaporates, (e) Does a transparent "spot" remain ? (/) If so, what is the cause of it ? 2. Stir the sample of paint and then place 2 or 3 drops of it on a cavity in the piece of charcoal. Heat this gently in the oxi- dizing flame of the blowpipe until any oil present burns away ; then increase the heat for two or three minutes. Any white lead present is reduced to metallic lead ; while any zinc oxide pres- ent will form a coating which is yellow while hot, but becomes white on cooling. In this way test samples for white lead and zinc and (g) record your results. 3. Coat a wooden splint with white paint and place it in water containing a few drops of ammonium sulfide. (h) Interpret your results. (/) What would be the result of painting the in- terior of a chemical laboratory with white-lead paint ? [157] EXERCISE 107 A STUDY OF SOME OF THE COMPOUNDS OF MANGANESE Apparatus. 6 test tubes. Materials, o.i to 0.2 g. potassium permanganate (KMn0 4 ); crystal of ferrous sulfate; sulfuric acid; ammonium sulfide (R. S.); ammo- nium carbonate (R. S.); sodium hydroxide; manganese chloride solu- tion (R. S.). 1. (a) Examine the physical properties of potassium perman- ganate. Dissolve about o.i g. of it in 5 cc. of water. Add a drop of the solution to a solution of the ferrous sulfate contain- ing 2 or 3 drops of sulfuric acid. The ferrous sulfate is changed to ferric sulfate, the oxygen in the reaction (see equation below) coming from the permanganate, which is a good oxidizing agent. 2 FeS0 4 +H 2 S0 4 + - ^Fe 2 (SO 4 ) 3 + H 2 O 2. In potassium permanganate the manganese acts as an a jid- forming element. It also acts as a base-forming element in certain compounds. Try the action of ammonium sulfide, am- monium carbonate, and sodium hydroxide, respectively, on a solution of manganese chloride, (b) Describe the results and write the equations for the reactions involved. EXERCISE 108 A STUDY OF SOME OF THE COMPOUNDS OF CHROMIUM Apparatus. 6 test tubes. Materials. Solution of potassium chromate (R.S.) ; lead acetate solution (R. S.); barium chloride solution (R. S.) ; ammonium sul- fide (R.S.) 5 sodium carbonate solution (R.S.) ; sodium hydroxide; chromium sulfate solution (R. S.). 1. (a) Chromates and dichromates. Write the formula for potassium chromate; for potassium dichromate. (b} Is the chromium an acid-forming or a base-forming element in these [1581 compounds? Add 2 or 3 drops of sulfuric acid to a little potassium chromate solution, (c) Explain the results. 2. Try the effect of a solution of potassium chromate on a solution of a compound of lead ; also on a compound of barium. (d) Describe the results and write the equations for all the reactions involved. 3. Salts of chromium. Try the effect of the following re- agents on a solution of a salt of chromium : ammonium sulfide, sodium carbonate, sodium hydroxide, (e) Describe the results and write the equations for all the reactions. EXERCISE 109 THE DETECTION OF SILVER, LEAD, AND MERCURY WHEN PRESENT IN THE SAME SOLUTION (OPTIONAL) Apparatus. Two beakers; stirring-rod; funnel; test tubes. Materials. Solutions of silver nitrate (R.S.), lead acetate (R.S.), and mercurous nitrate (R.S.) ; hydrochloric acid; filter paper; potassium chromate (R. S.); ammonium hydroxide; nitric acid; hot water; litmus paper (blue). 1. The detection of any one metal becomes more complicated when other metals are present in the same solution. As a rule it is necessary so to treat the mixture as to separate the metals from each other. The principle involved is illustrated in the following experiment. Pour into a beaker 5 cc. of the silver nitrate solution and 2 cc. each of the solutions of lead acetate and mercurous nitrate. Dilute with water to about 200 cc. Now add hydrochloric acid, drop by drop, with constant stirring. The precipitate formed on stirring settles to the bottom of the beaker. Continue add- ing the acid until a drop of it no longer causes a precipitate when brought in contact with the clear liquid in the beaker. (a) Write the equations for the reactions involved, (b) Re- cord the names and formulas of the compounds constituting the precipitate. Filter off the precipitate and fill the filter paper f 1591 with boiling water, collecting the filtrate in a beaker. The hot water dissolves the lead chloride so that this compound is present in the filtrate. Test for it by adding to the filtrate a few drops of potassium chromate solution. Yellow lead chro- mate is precipitated. It is important that all the lead chloride should be removed from the mixture on the filter paper ; hence again fill the filter paper with hot water. Wait until it runs through, and again repeat the process, discarding the filtrates. (c) What is the residue on the filter paper? To this residue add 2 or 3 cc. of ammonium hydroxide and collect the filtrate in a test tube. This filtrate contains the silver chloride dis- solved from the residue by the ammonium hydroxide. To prove its presence, neutralize the ammonium hydroxide present by adding nitric acid to the liquid until just acid to litmus paper. The silver chloride is precipitated. (d) What effect did the ammonium hydroxide have upon the color of the residue on the filter paper? This change in color is due to the action of ammonium hydroxide on the mercurous chloride, and serves as a test for the presence of the latter. (e) Supposing that the original solution contained only one or two of the metals of the group, how would the absence of the remaining ones be indicated ? EXERCISE 110 BORAX-BEAD TESTS (OPTIONAL) Apparatus. Platinum wire. Materials. Borax (R. S.) ; small piece (size of a pin's head) of a compound of each of the following metals : nickel, iron, manganese, copper. 1. Recall the effect of adding a trace of cobalt nitrate to a borax bead (Exercise 72). Repeat the experiment, substi- tuting for the cobalt nitrate, salts of the following metals: nickel, iron, manganese, copper, (a) Record your results. 1.160] APPENDIX THE METRIC SYSTEM With four or five exceptions this system is now used in all civil- ized countries. The United States and Great Britain are among the few countries that have not formally adopted it, but even in these countries the system is universally used by scientists and is coming into use more and more by manufacturers. In the metric system each unit is ten times as large as the next lower unit; hence the system is often termed the "decimal system." 1. Length. The unit is the meter. It is equal to 39.37 inches. 10 millimeters (mm.) = i centimeter (cm.) 10 centimeters = i decimeter (dm.) 10 decimeters = i meter (m.) 1000 meters = i kilometer (km.) The only measures of length ordinarily used by the chemist are the millimeter and the centimeter ; thus, the height of the barome- ter at the sea level is recorded as 76 cm. (or more commonly as 760 mm.) and not 7 dm. and 6 cm. 2. Volume. The unit generally used is the cubic centimeter. 1000 cubic millimeters = i cubic centimeter (cc.) 1000 cubic centimeters = i cubic decimeter = i liter 1000 cubic decimeters = i cubic meter The chemist uses only the cubic centimeter and the liter as measures of volume. Thus, the volume of a test tube is given as (say) 25 cc.; that of a flask as (say) 500 cc., or % liter. [1611 3. Weight. The unit is the gram. This is approximately the weight of i cc. of pure water at its temperature of greatest den- sity (4). It is equal to 15.43 grains. * 10 milligrams (mg.) = i centigram (eg.) 10 centigrams = i decigram (dg.) 10 decigrams = i gram (g.) 1000 grams = i kilogram (kg.) The gram and kilogram are the units of weight most generally used by the chemist. Thus, the weight of a crucible is given as (say) 10.532 g. and not 10,532 mg. or 10 g. 5 dg. 3 eg. 2 mg. RELATION BETWEEN ENGLISH AND METRIC CONSTANTS i pound (troy) = 373.24 grams i ounce (troy) = 31.10348 grams i pound (avoirdupois) = 453.59 grams i ounce (avoirdupois) = 28.3495 grams i kilogram = 2.67923 pounds (troy) i kilogram = 2.20462 pounds (avoirdupois) i liter = 1.05668 United States quarts ^ i gallon = 3.78543 liters i cubic centimeter = 0.06 10 cubic inch i cubic inch =16.3872 cubic centimeters i cubic foot = 28,320 cubic centimeters i centimeter = 0.3937 inch i meter = 39.37 inched Also note that i centimeter = nearly f inch . i meter = nearly i.i yards i kilogram = nearly 2\ pounds avoirdupois [ 162 TABLE OF SOLUBILITIES OF SOME OF THE COMPOUNDS OF THE METALS ACETATE BROMIDE CARBONATE CHLORATE CHLORIDE CHROMATE HYDROXIDE IODIDE NITRATE 1 PHOSPHATE SILICATE (ORTHO) SULFATE SULFIDE Aluminium .... w w W W A W W A A A W A Ammonium . . . w w W W W W W w w W w W Barium w w A W W A W w w A A A I W Calcium w w A W W X W w w X A A X X Cobalt w w A w w A A w w A A A w A Copper w w A w w W A w w A A A w A Ferric w w w w W A w w A A A w A Ferrous w w A w w A w w A A A w A Lead w X A w X A A X w A A A I A Magnesium w w A w w W A w w A A A w A Manganese w w A w w W A w w A A A w A Mercuric .... w w A w w X A w A A X I Mercurous .... w A w A A A w A A X Nickel w w A w W A A W w A A A w A Potassium .... w w W w W W W W w W W W w W Silver w I A w I A I w A A X A Sodium w w W w w W W W w W W W w W Stannic w w w A W A A A Stannous .... w w w A A w A A w A Zinc . ..... w w A w w W A w w A A A w A W, soluble in water. A, insoluble in water; soluble in either HC1 or HNO 3 or in both. I, insoluble in water and in acids. X, slightly soluble in water and slightly or readily soluble in acids. [ 1631 TREATMENT IN CASE OF ACCIDENT Every laboratory should be supplied with the materials neces- sary for the treatment of cuts and burns. Such wounds when im- mediately and intelligently treated give little or no trouble, but if left to take care of themselves infection may occur and serious results follow. In case of severe wounds the student, after the pre- liminary treatment in the laboratory, should be sent to a physician. The following materials required for the treatment of wounds should be kept in the laboratory in a tight cabinet or cupboard : 1. Plain, sterile gauze bandage : 6 rolls, i in. x 10 yd.; 6 rolls, 2 in. x 10 yd. 2. Adhesive plaster for holding gauze in place : 2 rolls, 0.5 in. x 10 yd. 3. 1000 cc. of benzine (low-boiling gasoline). 4. 2000 cc. of Seiler's solution (this may be made from tablets pur- chased at any drug store). 5. Boric acid solution prepared by dissolving 20 g. of boric acid in 1000 cc. of water. 6. Iodine solution ordinary tincture of iodine (this may be pur- chased at any drug store). 7. Agnew's solution prepared after the following prescription: Tannic acid 2 grams Borax 2 grams Glycerin n milliliters Camphorated water . . . q. s. to make 90 milliliters Different wounds should be treated as follows : 1. Cuts from glass. Remove any dirt or grease from the wound and surrounding skin by washing with gauze saturated with benzine. A rather free bleeding at first will help to prevent infection. Finally, wash the wound with a piece of gauze saturated with the iodine solu- tion; then bandage so as to prevent contamination. 2. Burns. Immediately apply gauze saturated with Seiler's solution and then bandage. 3. Burns from acids. Treat the same as ordinary burns, as directed under 2. 4. Burns from alkalies. Immediately wash with a large volume of water and then with boric acid solution on gauze ; then bandage. [164] 5. Acid in eyes. Immediately wash the eyes with a large volume of water, then with a solution of boric acid. Finally, drop into the eyes 3 or 4 drops of Agnew's solution and then apply to the eyes a small gauze pad which is kept saturated with ice water. INFORMATION REGARDING APPARATUS AND CHEMICALS The lists following include the apparatus and chemicals required for the experiments in this notebook. It is always best to furnish each student with as complete an outfit as possible and to hold him responsible for it. Certain pieces may, however, be used in com- mon by a number of students, and these have been placed in a separate list. It is always cheapest to purchase the apparatus and chemicals in as large quantities as possible. The amounts of most of the chemicals needed for a class of ten are so small that their cost will be proportionately much greater than when larger quan- tities are ordered. It is always best to order the definite amounts of chemicals listed in the catalogues, such as 100 g. or i lb.; otherwise the cost of weighing out odd quantities and preparing these for shipment may amount to more than the cost of the chemicals. The supplies may be obtained from any of the large dealers. Catalogues will be sent on application and should be in every school. The following are the addresses of some of the largest firms: Burrell Technical Supply Co., Pittsburgh, Pa.; Central Scientific Company, Chicago, 111. ; The Chemical Rubber Co., Cleveland, Ohio; Chicago Apparatus Co., Chicago. 111.; Kauffman-Lattimer Co., Columbus, Ohio ; L. E. Knott Apparatus Co., Boston, Mass. ; Eimer and Amend, New York City ; Standard Scientific Co., New York City; Scientific Materials Co., Pitts- burgh, Pa. ; E. H. Sargent & Co., Chicago, 111. ; Arthur H. Thomas Company, Philadelphia, Pa.; W. M. Welch Mfg. Co., Chicago, 111. ; The Will Corporation, Rochester, New York. A list of the supplies needed should be sent to a number of firms for quotations on prices. In ordering any piece of apparatus a certain form in some catalogue should be designated; other- wise it will be impossible to compare the prices. In general it is best to purchase as simple a form of apparatus as possible; for example, 20 cents will buy a Bunsen burner which for ordinary [165] purposes is preferable to those costing $i. A person experienced in the purchase of supplies will always find it possible to reduce materially the cost of the order. It is generally cheaper to purchase from local stores ordinary pieces of apparatus and materials commonly sold by such stores, rather than to order them through supply houses. Thus, an iron spoon can be purchased at any local five-and-ten-cent store and will cost less than when purchased through a supply house. Simi- larly, common salt can be obtained at a lower cost at the corner grocery than through a supply house. A few substances are listed that are not ordinarily furnished by supply houses. Thus, such houses do not ordinarily list "natural rubber," but this can be purchased at a trifling cost from any manufacturer of rubber tires or other rubber commodities. Denatured alcohol may be used where alcohol is specified, but it is better to use the pure alcohol. This can be secured tax free from supply houses by presenting a per- mit secured from the Federal prohibition officer of your state. Such alcohol must be kept by the instructor and given out to students only on signed blanks giving the use for which the alcohol is desired. Materials purchased of supply houses should be ordered at least three or four months in advance, for the rate of delivery is often very slow. It is best for the teacher, during the spring months, to make up and place the entire order for the following academic year. The teacher should be careful in giving exact specifications and should insist on getting what he orders. All materials not in accord with the specifications should be promptly returned; otherwise his laboratory may become the dumping ground for poor or off-sized materials. It makes a wide difference in the student's work whether or not he is compelled to use (say) glass tubing that is off size and corks that do not fit. The right size costs no more. Be sure to specify it and then insist on getting it. APPARATUS REQUIRED FOR EACH STUDENT (TO BE KEPT IN STUDENT'S LOCKER) Beakers, nest of seven, from loo-cc. to yoo-cc. Blowpipe, mouth. Bottles, wide-mouthed: one, 6o-cc.; five, 250-00. [ 1661 Burner, wing-top, for bending glass tubing (Fig. 12). Calcium chloride drying-tube, straight, 15 cm. in length (Fig. 37, B). Charcoal, i piece about 8 cm. x 3 cm. x 2 cm. Copper gauze, 10 cm. x 12 cm., from 60 to 70 mesh. Deflagra ting-spoon. Dish, lead, diameter about 6 cm., depth 3 cm. Evaporating-dish, diameter 7 cm. Files : round, about 15 cm. in length ; triangular, about 15 cm. in length. Filters, 25, diameter about n cm. Florence flasks: two, 25o-cc.; one, soo-cc. Forceps (steel), 10 cm. long. Funnel, diameter about 6.5 cm. Funnel tube, external diameter of tube 6 mm. Glass tubing : 300 g., soft, external diameter 6 mm., walls i mm. thick; i piece, hard-glass, 30 cm. in length, internal diameter 1.5 cm., walls 1.8 mm. thick; i piece, hard glass, 25 cm. in length and 6 mm. internal diameter. Glass rod, diameter 2 mm., i piece. 30 cm. in length. Medicine dropper. Mortar (diameter about 8 cm.) and pestle (both of porcelain). Pipestem triangle for holding porcelain crucible (Fig. 30). Platinum wire, small (No. 28), 5 cm. long, for flame tests. Porcelain crucible and lid, diameter about 3.5 cm. Rubber tubing: internal diameter 5 mm., i piece 50 cm. in length; soft, pure gum, internal diameter 5 mm., i piece 30 cm. in length for connections etc. Screw clamp for rubber tubing. Splints (ordinary cigar lighters), 125. Sponge. Spoon, ordinary iron, bowl 5 or 6 cm. long. Stoppers : rubber, one-hole, to fit the hard-glass test tube ; rubber, two- hole, to fit wide-mouthed 25o-cc. bottle; rubber, two-hole, to fit 250-cc. flask; rubber, two-hole, to fit looo-cc. narrow-mouthed bottle. Stoppers, rubber, 2 one-hole, to fit the hard-glass tubing specified above. Test tube, graduated, 3o-cc., about 20 cm. long, with o.5-cc. graduations. Test tube, hard-glass, 15 cm. in length, diameter about 1.8 cm. Test tubes, 12, length 15 cm., diameter about 1.5 cm. Test-tube brush. Test-tube rack. Towel. [167] Tripod. Watch glass, diameter about 8 cm. Window glass, 4 pieces 10 cm. square. Wire gauze, 2 pieces 12 cm. square. APPARATUS TO BE LEFT ON EACH DESK Bunsen burner, with 75 cm. of rubber tubing to fit. Clamp, iron, large, for holding flasks and condensers. Iron tripod (Fig. 58). Pneumatic trough (Fig. 28). The trough should be about 12 to 15 cm. deep, and large enough to hold 4 or 5 wide-mouthed bottles (25o-cc.). It may be round or rectangular. A pan made of granite ware or an earthen crock serves well, or any tinsmith can readily make suitable troughs of galvanized iron. Ring stand and 3 rings. Sand bath, iron, about 12 cm. in diameter. REAGENTS ON EACH DESK 250-cc. bottles filled with the reagents named below. The bottle con- taining the sodium hydroxide should have ordinary corks, the others should be glass-stoppered. Ammonium hydroxide (density 0.90). Hydrochloric acid (density 1.2). Nitric acid (density 1.4). Sodium hydroxide solution (10 g. in 100 cc. of water). Sulfuric acid (density 1.84). GENERAL APPARATUS FOR TEN STUDENTS Apparatus marked with a star (*) are required for optional experiments. *2 sets apparatus for testing conductivity of solutions (Fig. 62) ; this may be made or may be purchased of supply houses. *i Babcock milk-test apparatus complete, either two- or four-bottle (Fig. 76). 1 balance, weighing from 0.5 g. to 500 g., with accompanying weights. 2 balances, sensitive to i eg. and made to carry a load of 100 g. with accompanying weights (each set from i eg. to 50 g. in covered wooden box), i barometer. 5 one-liter, narrow-necked bottles, i bottle or flask, 2ooo-cc. (Fig. 43, B). 4 burettes, 5o-cc., graduated in o.i cc. (Fig. 61). [168] 5 pieces cobalt glass 10 cm. square (for flame tests). *4 condensers (Liebig), with rubber tubing. 2 sets cork borers (6 in a set), and sharpener. 2 gross corks, best grade, sizes 7, 8, 9, 10, and 12. i cylinder, graduated, loo-cc. i cylinder, graduated, 5oo-cc. i distilling apparatus for preparing distilled water. i magnifying glass, small. i microscope, eyepiece i inch, objectives f and . 5 graduated pipettes (5 cc., graduated in divisions of o.i cc. or 0.2 cc.). *i spectroscope (Fig. 84). 5 thermometers, graduated from 10 to 150 C. 5 retorts, glass-stoppered, iso-cc. (Fig. 65). 5 porcelain boats about 8 cm. in length and 6 or 7 mm. wide (these must be of such a size as to slip easily into the hard-glass tub- ing, specified under the heading "Apparatus required for Each Student"). CHEMICALS ON REAGENT SHELF (FOR USE OF ALL STUDENTS) The bottles containing solutions should be glass-stoppered. Gummed letters of the alphabet, of different sizes, may be ob- tained at a little cost from the Tablet and Ticket Co., Chicago, 111., and these may be used in making the labels for the bottles ; or the complete labels for all the common chemicals may be pur- chased from supply houses. If the class is small, bottles holding 250 cc. will ordinarily serve; if the class is large, then it is better to use bottles holding at least 500 cc. A few of the reagents, such as limewater, are used so extensively that it is better to use a looo-cc. bottle. Distilled water must be used in making all solutions. A 10 per cent solution signifies 10 g. dissolved in 100 cc. of water. Acetic acid (36 per cent). Aluminium sulfate (10 per cent solution). Ammonium carbonate (25 g. of the solid dissolved in 70 cc. of water and 10 cc. of ammonium hydroxide (density 0.90), and the solution diluted to 100 cc. with water). Ammonium chloride (10 per cent solution). Ammonium molybdate solution (obtained directly from dealers). Ammonium sulfide solution (obtained directly from dealers). Barium chloride (10 per cent solution). [ 1691 Borax (solid). Calcium chloride (10 per cent solution). Carbon tetrachloride. Chloroform. Chlorine water (water saturated with chlorine). Chromium sulfate (10 per cent solution). Cobalt nitrate (5 per cent solution). Copper sulfate (10 per cent solution). Disodium phosphate (10 per cent solution). Fehling's solution : solution A, prepared by dissolving 17.5 g. of copper sulfate crystals in 250 cc. of water; solution B, prepared by dis- solving 87.5 g. of sodium potassium tartrate in 250 cc. of 10 per cent sodium hydroxide solution. Ferric chloride (10 per cent solution). Ferric sulfate (10 per cent solution). Hydrogen sulfide solution. Prepared by passing hydrogen sulfide slowly through water until the water is saturated with the gas. Since the solution loses its strength after a few days, it is necessary to pre- pare it as needed. Iodine solution. Prepared by dissolving 2 g. of iodine and log. of potassium iodide in 100 cc. of water. Lead acetate (10 per cent solution). If the solution is not clear, add a few drops of acetic acid and shake the mixture ; repeat until the solution becomes clear. Limewater (saturated solution of calcium hydroxide). Shake 3 or 4 g. of the solid hydroxide with i liter of water ; then set the mixture aside until the excess of solid settles. Use the clear supernatant liquid. Litmus solution. Dissolve sufficient litmus (litmus cubes) in the water to impart to it a deep color. Magnesium sulfate (10 per cent solution). Manganese chloride (10 per cent solution). Mercuric chloride (5 per cent solution). Mercurous nitrate (10 per cent solution). Phenolphthalein (i g. dissolved in 200 cc. of alcohol). Potassium bromide (10 per cent solution). Potassium chromate (10 per cent solution). Potassium ferrocyanide (10 per cent solution). Potassium hydroxide (10 per cent solution). Potassium iodide (10 per cent solution). Potassium sulfocyanate (10 per cent solution). Silver nitrate (4 per cent solution). [1701 Starch solution. Prepared by rubbing to a thin paste 4 or 5 g. of starch with cold water and then adding, 3 or 4 drops at a time and with stirring, to i liter of boiling water. Add also about 10 g. of zinc chloride (this acts as a preservative). Mix thoroughly, set the mix- ture aside, and use the clear supernatant liquid. Sodium carbonate (10 per cent solution). Sodium chloride (solid). Sodium thiosulfate (10 per cent solution). Zinc acetate (10 per cent solution). CHEMICALS REQUIRED FOR A CLASS OF TEN The terms in parentheses after the names of the chemicals refer to the grade of materials to be purchased. The abbreviation c.p. signifies " chemically pure." The weights required in each case are given in the metric system, but there is also added the approxi- mate English equivalent. Those chemicals marked with a star (*) are for optional experiments. This list does not include substances always easily obtained at home stores, such as baking powders, butter, clay, cloth, fats of various kinds, flour, gasoline, gelatin, ice, iron and copper wire, kerosene, lead, milk, molasses, oleomargarine, salt, soap, starch, sugar, tacks, vinegar, yeast, etc. APPROXIMATE AMOUNTS Acid, acetic (36 per cent) (c.p.) 500 g. (i Ib.) Acid, acetic (glacial) 200 g. (^ Ib.) *Acid, formic (50 per cent) 2Op g. ( Ib.) Acid, hydrochloric (density 1.2) (c.p.) 2 kg. (5 Ib.) Acid, hydrochloric (commercial) for use in preparing carbon dioxide 2 kg. (5 Ib.) Acid, nitric (density 1.4) (c.p.) 3 kg. (7 Ib.) *Acid, oxalic (pure) 200 g. Q Ib.) Acid, sulfuric (density 1.84) (c.p.) 4 kg. (9 Ib.) *Acid, sulfuric (commercial) (density 1.83) for Bab- cock milk test 500 g. (i Ib.) Acid, tannic (commercial) 100 g. ( Ib.) Alcohol (95 per cent) i liter (i qt.) Alum (ammonium) pure 500 g. (i Ib.) Aluminium (turnings or filings) 30 g. (i oz.) Aluminium sulfate (pure, crystals) 500 g. (i Ib.) Ammonium carbonate (pure) 100 g. (i Ib.) [171] APPROXIMATE AMOUNTS Ammonium chloride (pure) 200 g. ( Ib.) Ammonium hydroxide (density 0.90) (c.p.) ... 2 kg. (5 Ib.) Ammonium molybdate solution 500 g. (i Ib.) Ammonium nitrate (pure) 100 g. (^ Ib.) Ammonium sulfate (commercial) 500 g. (i Ib.) Ammonium sulfide solution 500 g. (i Ib.) Aniline 100 g. (3 oz.) Antimony 30 g. (i oz.) Arsenic 30 g. (i oz.) Arsenic trioxide (arsenious oxide) (commercial) . . 30 g. (i oz.) Barium chloride (c.p.) 100 g. ($ Ib.) Barium nitrate (crystals) 100 g. ( Ib.) Barium sulfate 500 g. (i Ib.) Benzene 200 g. (i Ib.) Bismuth . 30 g. (i oz.) Bleaching-powder 500 g. (i Ib.) Boneblack . . . .... . . . . . . 200 g. ( lb.) Borax (commercial) 500 g. (i lb.) Boric acid (pure) . . . 100 g. ( lb.) Cadmium chloride (c.p.) 30 g. (i 03.) Calcium carbide 500 g. (i lb.) Calcium carbonate (precipitated) . . . .' . . 500 g. (i lb.) Calcium chloride (fused or granular) for filling drying tubes i kg. (2 lb.) Calcium fluoride (fluorspar) 200 g. Q lb.) Calcium hydroxide (hydra ted lime) 500 g. (i lb.) Calcium sulfate (plaster of Paris) i kg. (2 lb.) Carbon disulfide (commercial) 100 g. (4 oz.) Carbon tetrachloride (commercial) 2 kg. (5 lb.) Charcoal (small pieces) 500 g. (i lb.) Chloroform (commercial) 200 g. ( lb.) Chromium sulfate 30 g. (i oz.) Cobalt nitrate (pure) 30 g. (i oz.) Cobalt chloride 30 g. (i oz.) Copper (turnings or scrap) 200 g. Q lb.) Copper foil (thin) 100 g. ( lb.) Copper nitrate (pure) 30 g. (i oz.) Copper oxide (black, finely powdered) 100 g. (^ lb.) Copper sulfate crystals (c.p.) 200 g. (% lb.) Cottonseed oil 200 g. (i lb.) [172] APPROXIMATE AMOUNTS Cyanamide (commercial) i kg. (2 Ib.) Dyes : Gallein, fuchsine, methyl violet, malachite green, Congo red 10 g. of each alizarin paste (20 per cent) . 100 g. ( Ib.) Formalin 100 g. ( Ib.) Gypsum (crystals) 200 g. (i Ib.) Hydrogen peroxide 200 g. ( Ib.) Iodine 30 g. (i oz.) Iron chloride (ferric) (c.p.) 60 g. (2 oz.) Iron powder (iron reduced by alcohol) 100 g. (^ Ib.) Iron sulfate (ferrous) 200 g. (J Ib.) Iron sulfide (ordinary lumps for preparing hydrogen sulfide) i kg. (2 Ib.) Iron wire (picture-frame wire), No. o 25m. (25yd.) Junket tablets (obtained from any grocer or druggist) 10 tablets Lead acetate (sugar of lead) (powdered) .... 200 g. Q Ib.) Lead monoxide (commercial) 100 g. (J Ib.) Lead nitrate (pure) 60 g. (2 oz.) Litmus cubes 60 g. (2 oz.) Litmus paper (100 strips red, 100 strips blue) ... 2 tubes of each Magnesium carbonate (powdered) 100 g. ( Ib.) Magnesium sulfate (Epsom salts) 500 g. (i Ib.) Magnesium wire or ribbon 30 g. (i oz.) Manganese chloride 60 g. (2 oz.) Manganese dioxide (pure, powdered) i kg. (2 Ib.) Marble (pieces size of a walnut) 2 kg. (5 Ib.) Mercuric chloride (corrosive sublimate) . . . . 30 g. (i oz.) Mercuric nitrate (c.p.) 30 g. (i oz.) Mercuric oxide 30 g. (i oz.) Mercurous nitrate (c.p.) 100 g. (i Ib.) Mercury 30 g. (i oz.) Nickel nitrate 30 g. (i oz.) Paraffin 500 g. (i Ib.) Phenolphthalein 30 g. (i oz.) Phosphorus (white) 20 g. (i oz.) Photographic developer i tube Portland cement i kg. (2 Ib.) Potassium bitartrate (cream of tartar) .... 100 g. (^ Ib.) Potassium bromide (granular, pure) . . . . . 60 g. (2 oz.) Potassium carbonate (c.p.) 60 g. (2 oz.) [173] APPROXIMATE AMOUNTS Potassium chlorate (small crystals) 500 g. (i Ib.) Potassium chloride (c.p.) 100 g. (i Ib.) Potassium chromate or sodium chromate (pure) . . 100 g. (i Ib.) Potassium chromium sulfate (chrome alum) . . . 100 g. ( Ib.) Potassium dichromate (pure) 100 g. Q Ib.) ^Potassium ferrocyanide (c.p.) 100 g. ($ Ib.) Potassium hydroxide (sticks) 100 g. ( Ib.) Potassium iodide (pure) 60 g. (2 oz.) Potassium nitrate (pure) 200 g. ( Ib.) Potassium permanganate (pure) 30 g. (i oz.) Potassium sulfate (pure, anhydrous) 100 g. ( Ib.) *Potassium sulfocyanate (c.p.) . . 30 g. (i oz.) Rubber (natural) . . . . . . Jf . .-..,. 500 g. (i Ib.) Silver nitrate . . . , ; . 30 g. (i oz.) Soda lime (granular) . . . -.- -.-. . , <..-;., 500 g. (i Ib.) Sodium ..,.*, 30 g. (i oz.) *Sodium acetate (fused) 500 g. (i Ib.) *Sodium benzoate (pure) . . . . . . . . 30 g. (i oz.) Sodium bicarbonate (baking-soda) ;.';, 500 g. (i Ib.) Sodium bromide (crystals) (pure) ...... 200 g. ( )b.) Sodium carbonate (pure, anhydrous) 200 g. (I Ib.) Sodium hydrogen phosphate (disodium phosphate) (c.p.) '. 100 g. (J Ib.) Sodium hydroxide (sticks) . i kg. (2 Ib.) Sodium hydroxide (normal solution) i liter Sodium iodide (crystals) (pure) 100 g. ( Ib.) Sodium nitrate (pure) 200 g. (^ Ib.) Sodium potassium tartrate (Rochelle salts) (powdered) 500 g. (i Ib.) Sodium silicate solution (water glass) . . .... 500 g. (i Ib.) Sodium sulfate (crystals) (Glauber's salt) . .... 200 g. (^ Ib.) Sodium thiosulfate . 500 g. (i Ib.) Sulfur (flowers) 500 g. (i Ib.) Sulfur (roll) 500 g. (i Ib.) Tartar emetic (potassium antimonyl tartrate) . 60 g. (2 oz.) Tin (mossy) , 60 g. (2 oz.) Zinc (mossy, arsenic-free) ; i kg. (2 Ib.) Zinc (sheet) . 200 g. Q Ib.) Zinc chloride 100 g. ( Ib.) Zinc sulfate (crystals) ... 100 g. (i Ib.) *Zinc sulfide ' . . , ~ . . . 30 g. (i oz.) [174] TABLE OF CONSTANTS LIST OF THE COMMON ELEMENTS, THEIR SYMBOLS, THEIR ATOMIC WEIGHTS AND = - 16 Aluminium . . Al 27.1 Iodine . . . . I 126.92 Antimony .' Sb I2O.2 Iron . . . . Fe 55.84 Arsenic . . As 74.96 Lead . . . . Pb 207.2 Barium . . Ba 137-37 Magnesium . Mg 24.32 Bismuth . . . Bi 208.0 Manganese . Mn 54-93 Boron . B II.O Mercury . . Hg 200.6 Bromine . . Br 7Q.Q2 Nickel . . . . Ni 58.68 Cadmium . Cd II2.4 Nitrogen . . . N 14.01 Calcium . . Ca 40.07 Oxygen . 16.0$ Carbon . . C 12. OO Phosphorus . P 31.04 Chlorine . . Cl 3546 Potassium . . K 39-1 Chromium . . Cr 52.0 Silicon . , . . Si 28.3 Cobalt . . . Co 58.97 Silver . . Ag 107.88 Copper . . . Cu 63.57 Sodium . . Na 23.0 Fluorine . . F I9.O Sulfur . . . . S 32.06 Gold . . . v > Au 107. 2 Tin. . . . Sn 118.7 Hydrogen . H V / * 1.008 Zinc . 4 . Zn -.****! 65.37 TENSION OF AQUEOUS VAPOR AT VARIOUS TEMPERATURES, EXPRESSED IN MILLIMETERS OF MERCURY TEMPERATURE 15 16 . . . 17 . . . 18 . . . 19 . . . 20 . PRESSURE TEMPEKATURE PRESSURE . 12.78 ^21 18.62 . 13.62 ^2 ....... 19.79 . 14.52 23 . . . . . . . 21.02 . 15.46 24 22.32 . 16.56 25 23.69 . 17.51 100 760.00 WEIGHT IN GRAMS OF 1 LITER OF VARIOUS GASES MEASURED UNDER STANDARD CONDITIONS Acetylene . . . . 1.1621 Air 1.2928 Ammonia .... 0.7708 Carbon dioxide . . . 1.9768 Carbon monoxide . . 1.2504 Chlorine 3.1674 Hydrogen .... 0.08987 Hydrogen chloride . . 1.6398 Hydrogen sulfide . . . 1.5392 Methane 0.7168 Nitric oxide .... 1.3402 Nitrogen 1.2507 Nitrous oxide. . . . 1.9777 Oxygen 1.4290 Sulfur dioxide . . . . 2.9266 TABLE OF SOLUBILITY OF VARIOUS SOLIDS WEIGHT DISSOLVED BY 100 cc. OF WATER AT ^tTR^TA Wf"H o 20 100 Calcium chloride . CaCl 2 59-5 g- 74-5 g. JSQ-og- Sodium chloride . . . NaCl 35-70 g. 3 6 - g- 39.80 g. Potassium nitrate , KNO 3 1 3-30 g. 3i-6 g- 246.0 g. Copper sulfate . . . CuSO 4 14-3 g- 21.7 g. 75-4g- Calcium sulfate . . . CaS0 4 0-7 59 g- 0.203 g. 0.162 g. Calcium hydroxide . . Ca(OH) 2 0.185 g- o.i65g. 0.077 g- DISPLACEMENT (ELECTROCHEMICAL) SERIES 1. Potassium 2. Sodium 3. Lithium 4. Calcium 5. Magnesium 6. Aluminium 7. Manganese 8. Zinc 9. Chromium 10. Iron 11. Cobalt 12. Nickel 13- Tin 14. Lead 15. Hydrogen 1 6. Copper 17. Arsenic 1 8. Bismuth 19. Antimony 20. Mercury 21. Silver 22. Platinum 23. Gold [176] YB 36034 568038 UNIVERSITY OF CALIFORNIA LIBRARY