length, connects the glass tube with a small funnel, as shown in the figure.

Close the rubber tube tightly with the screw clamp D. Disconnect the test tube and remove the glass rod B from the stopper preparatory to performing the experiment.

Add the solution of potassium hydroxide to the solution of pyrogallic acid, mix, and at once pour the resulting liquid into the funnel E. Quickly open the screw clamp D until the rubber tube and the glass tube are both filled with the liquid, and then close the clamp tightly.

Connect the test tube, holding it by the rim to avoid heating the contained air, and insert the glass rod in the cork. The air inclosed in the tube is now at the same temperature and pressure as the surrounding air.

Now open the screw clamp. The liquid flows in, absorbing the oxygen. When the liquid ceases to enter, grasp the tube by the rim and invert it, as shown by the dotted lines of the figure, adjusting it so that the level of the liquid is the same in both tube and funnel (?); then clamp the rubber tube tightly and return the test tube to its original position.

Mark the volume of the air originally inclosed in the tube by placing a narrow strip of gummed paper about the tube at the lower end of the stopper; mark also, by a strip of paper placed at the level of the liquid in the tube, the volume of the oxygen absorbed.

Disconnect the tube and rinse it. Measure the volume of the tube to each strip of paper by pouring in water from a graduated cylinder. From these measurements calculate the number of volumes of oxygen and nitrogen in 100 volumes of air.

NOTE. This experiment disregards the presence in the air of all constituents other than oxygen and nitrogen. The volume of such constituents, however, in the amount of air taken is smaller than the unavoidable errors in the experiment.

II. OTHER CONSTITUENTS OF THE AIR

a. Place a piece of calcium chloride on a watch glass and expose it to the air for two or more hours. What do the results indicate? (A substance which, like calcium chloride, takes up moisture on exposure to air is said to be deliquescent.)

b. Expose a few cubic centimeters of limewater to the air for a half hour. The formation of a white crust on the limewater proves the presence of carbon dioxide in the air (see p. 201 of text).

EXERCISE 19

A STUDY OF SOLUTIONS

Apparatus. 5 test tubes; watch glass; funnel; apparatus shown in Fig. 24, Exercise 14.

Materials. 2 g. sugar; 5 cc. alcohol; 0.2 g. calcium sulfate; 2 crystals of potassium permanganate; bit of soap size of a bean; 1 cc. cottonseed oil or kerosene; 25 g. common salt; filter paper; 3 g. potassium nitrate.

a. Place 1 g. of sugar in each of two test tubes. To the one test tube add 5 cc. of water and to the other 5 cc. of alcohol. Shake the contents thoroughly (?).

b. Place about 0.2 g. of calcium sulfate in a test tube and add 5 cc. of water. Shake the mixture thoroughly for a few seconds; then set the tube aside for five or ten minutes. Filter a few drops of the liquid, collecting the filtrate on a watch glass. Set the glass on a small beaker partially filled with boiling water (Fig. 31) until the filtrate is evaporated (?).

c. Nearly fill two test tubes with water and set them in a rack. Drop into each a small crystal of potassium permanganate. Shake the contents of one tube and repeat the shaking after a few minutes. At the close of the laboratory period note the appearance of the liquid in each tube (?).

d. Select two tubes, filling the one nearly full of distilled (or soft) water and the other with a like amount of distilled water in which a small bit of soap has been dissolved. Add

shake the contents vigorously for one minute; then set the tubes in the rack. Examine them at the close of the laboratory period (?).

e. Place exactly 3 g. of common salt in one test tube and an equal weight of potassium nitrate in another. Add to each exactly 1 cc. of water and heat the tube. If the solid does not dissolve, add an additional cubic centimeter of water and again heat. Repeat until the solid in each tube is dissolved. Compare the solubilities of the two solids in the boiling water. Cool the solutions in each tube and note the approximate amounts of solids separating (?) (compare the results with the table of solubility of solids given in the Appendix).

*f. Repeat Exercise 14, Experiments a and b, substituting a concentrated aqueous solution of common salt for the water (?).

EXERCISE 20

DETERMINATION OF THE SOLUBILITY OF COMMON SALT (QUANTITATIVE)

Apparatus. 60-cc. bottle; evaporating-dish with watch-glass cover; funnel; tripod and burner; thermometer.

Materials. 15 g. common salt; filter paper.

Place 15 g. of common salt in a 60-cc. bottle and add 40 cc. of water. Shake the mixture vigorously and set aside, repeating the shaking several times at intervals of from one or two minutes, so as to form a saturated solution. Note the temperature of the solution.

Accurately weigh the evaporating-dish and the watch-glass cover, then filter into the dish about 20 cc. of the saturated solution of salt, and weigh again. Set the watch glass aside and evaporate the solution (Fig. 31). After the solution has evaporated to dryness, 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. (Do you see any reason for using the watch glass ?)

Now withdraw the burner, and after the dish is cool (room temperature) weigh once more. From your results calculate the approximate number of grams of salt that will dissolve in 1 liter of water at the temperature of the original solution.

If time permits, the solubility of other substances such as calcium sulfate and potassium dichromate may be determined in like manner; or different students may select different substances and compare their results.

EXERCISE 21

A METHOD FOR DETERMINING WHETHER OR NOT A GIVEN LIQUID IS A CONDUCTOR OF ELECTRICITY (OPTIONAL)

Apparatus. As shown in Fig. 53 (p. 103 of text); current from electric-lighting system.

Materials. 1g. common salt dissolved in 25 cc. water; 1g. sugar in 25 cc. water; 5 cc. sodium hydroxide solution added to 20 cc. water; 5 cc. sulfuric acid added to 20 cc. water; tap or well water; 5 cc. hydrochloric acid added to 20 cc. water.

If an electric-lighting current is available, test the conductivity of the following substances as explained on page 103 of the text, using the apparatus shown in Fig. 53 of the text: (1) distilled water, (2) distilled water containing a few drops of sulfuric acid, (3) hard water from a well, (4) a solution of common salt, (5) a solution of sugar, (6) hydrochloric acid, (7) a solution of sodium hydroxide. The apparatus must be carefully cleaned with distilled water after testing each solution (?). Tabulate the results.

THE PROPERTIES OF ACIDS, BASES, AND SALTS

Apparatus. 3 small beakers; stirring-rod; evaporating-dish; ring stand and burner.

Materials. A few drops of each of the following acids: hydrochloric, sulfuric, nitric, acetic (R. S.); solutions of the following bases: sodium hydroxide, potassium hydroxide (R. S.), calcium hydroxide (R.S.); strips of blue and of red litmus paper.

a. Prepare a dilute solution of each of the following acids by adding 1 or 2 drops of the acid to 10 cc. of water: hydrochloric, nitric, sulfuric, acetic.

By means of a clean glass rod transfer a drop of each to a piece of blue litmus paper. Note the result. In a similar way try their effect on red litmus paper. Taste one drop of the dilute solutions (rinse the mouth with water after tasting).

Compare the formulas of the acids. In what respect are the acids similar in composition?

a

b. In a similar way try the effect on red litmus paper of solution of each of the following bases: sodium hydroxide, potassium hydroxide, calcium hydroxide. Do they affect the blue litmus paper? Taste a drop of the calcium hydroxide solution.

Compare the formulas of the bases. In what respect are the bases similar in composition?

c. Dilute 5 cc. of the ordinary laboratory solution of sodium hydroxide (1 part of the hydroxide to 10 parts of water) with an equal volume of water. To this solution add 4 or 5 drops of hydrochloric acid (R). Stir the resulting solution with a glass rod and test its action on blue and on red litmus paper. Has it acid or basic properties?

Now continue to add the acid drop by drop until the resulting solution is neutral (that is, has no effect on either blue or