the curved surface of the liquid. Pour the 5 c.c. of acid into an evaporating dish, rinse the test tube with 5 c.c. of water, and add the rinsings to the acid in the dish. Note what part of your evaporating dish is occupied by the resulting 10 c.c. of liquid, for comparison in e of this experiment. Add to the evaporating dish 3 drops of phenolphthalein solution.

c. Fill a burette with ten per cent potassium hydroxide solution. The burette is best fitted with rubber and a glass tip controlled by a pinch-clamp. If a glass stopcock is used see that it is well lubricated with vaseline. Support the burette in a clamp, put under it a beaker, and let the liquid run out until the part of the burette below the clamp is filled with liquid. Return the liquid which ran out to the burette. Read the level of the liquid exactly to tenths of a cubic centimeter, having your eye in the same horizontal plane with the bottom of the meniscus. Record this reading.

d. Open the clamp of the burette carefully, and let the potassium hydroxide solution fall drop by drop into the evaporating dish of dilute acid. Stir constantly. Get the solution exactly neutral, or at any rate have only one drop of alkali in excess.

Read the burette again. How much alkali was used? e. Evaporate the solution to about 12 c.c., and let it cool thoroughly. Result?

f. Repeat b, c, and d with twice the quantity of dilute acid, i. e., 10 c.c., and exactly as much potassium hydroxide as was used in d.

Test solution with litmus. Result?

resulting solution to 5 c.c., and let it cool.

Evaporate the

Result.

g. Dry the solid substance obtained in e between filter

NORMAL AND ACID SALTS CONTINUED.

45

papers. What is the general shape of the crystals? Heat one in a dry test tube. Has it crystal water? Treat some of the crystals with 1 to 2 c.c. water in a test tube. Are they easily soluble? What is the reaction of the solution to litmus? Its taste?

h. Treat the crystals obtained in ƒ as directed in g. Results? Are the crystals in the two cases alike?

How many salts does sulphuric acid form with potassium hydroxide, according to this experiment?

EXPERIMENT XXIX.

NORMAL AND ACID SALTS CONTINUED.

Apparatus.
Materials.

Same as in Experiment XXVIII.

Concentrated pure hydrochloric acid, ten per cent potassium hydroxide solution, phenolphthalein.

a. In the marked test tube (see Experiment XXVIII, a) measure out 5 c.c. concentrated hydrochloric acid, put this acid into an evaporating dish, and rinse the tube with 5 c.c. of water, as in Experiment XXVIII, b. Add phenolphthalein, and neutralize with ten per cent potassium hydroxide from the burette. Note the amount of alkali used.

b. Evaporate the neutral solution to dryness. Finally, heat the evaporating dish until no fumes of any kind come off, and even the crackling sound-decrepitation -practically ceases.

Let the dish cool thoroughly.

c. Examine the product, noting its solubility in water, the taste of the solution, and its reaction with litmus.

d. Repeat a, b, and c, with the same amount of alkali, but with twice the quantity, i. e., 10 c.c., of hydrochloric acid.

Be sure to evaporate as directed in b.

e. Compare results with those obtained in c. How many salts do you get hydrochloric acid to form with potassium hydroxide?

EXPERIMENT XXX.

IONIZATION.

Apparatus. Test tubes, mortar and pestle.

Materials. Solutions of silver nitrate, potassium chloride, potassium chlorate, sodium hydroxide, and potassium ferrocyanide; solid ferrous sulphate, sodium bicarbonate, and tartaric acid.

a. Double decomposition between two salts. Review Experiment XV, a, and write the equation here. In the double decomposition reactions of acids, bases, salts, and water, the materials that react may be classified under the following heads:

Classify the materials of the two salts of Experiment XV, a, under these heads.

Take 2 c.c. silver nitrate solution in each of two test tubes. To one add a few drops of potassium chloride solution. Write the equation, indicating the precipitate by an arrow (1). Classify the materials that react in this case also. Why is a precipitate formed?

To the other tube of silver nitrate add some pure potassium chlorate solution. Result? Write the equilibrium equation (2) for the reaction. Why is there no precipitate? Of what radical is the chlorine a part? b. Double decomposition between salts and bases. Powder about 1 c.c. of ferrous sulphate, FeSO4, and shake it with 5 c.c. of water. Pour off the solution, and add to it a few drops of sodium hydroxide solution. Result? If the precipitate has the formula Fe(OH)2, write the equation. Classify the materials that react in this case.

Treat about 3 c.c. of potassium ferrocyanide solution, K4Fe(CN)6, with a few drops of sodium hydroxide solution. Result? Why is Fe(OH)2 not precipitated as before? Of what radical is the iron a part?

c. Double decomposition between salts and acids. Review Experiments XV, b, XX, a, and XXII, m, and rewrite the equations here. Use the proper arrows for precipitates or escaping gases. Classify, as in a, the materials that react in the case of salts and acids.

Grind together about 1 c.c. each of sodium bicarbonate and tartaric acid in a dry mortar. Is there any evidence of a reaction? Now add water, and account for the difference. Write the equation (cf. § 280 of text).

d. Double decomposition between acids and bases. Review Experiments XXVII to XXIX. Write here the equations involved. Classify the materials of acids and bases that react by double decomposition. What one substance (not class) is always formed in neutralization? What materials unite to produce it? What becomes of the other two? For which materials do we test with indicators like litmus and phenolphthalein?

EXPERIMENT XXXI.

HYDROLYSIS AND REPLACEMENT.

Materials. Litmus paper, antimony chloride, bismuth nitrate, iron nails (brads), copper turnings, and zinc (strips or granulated); concentrated hydrochloric and nitric acids; solutions of aluminum chloride, cupric sulphate, mercurous nitrate, and silver nitrate.

a. To a small amount (half a c.c.) of antimony chloride, SbCl3, add 5 c.c. water, and shake the two together. Result? If the product first formed is antimony OH

dihydroxychloride, SbOH, write the equation.

Cl

b. To the precipitate add concentrated hydrochloric acid, a drop at a time, warming after each drop. Result? If the solution contains antimony chloride, SbCl3, write the equation.

c. Add the solution obtained in b to 50 c.c. water. Result? Add concentrated hydrochloric acid again. Result? d. Compare the equations of a and b. Write one of them, using, instead of the equality sign, the double arrow Z. In which direction does the reaction go chiefly when an excess of water is used? When an excess of acid is used?

e. Repeat the experiment with bismuth nitrate, Bi(NO3)3, and water, and use concentrated nitric acid instead of hydrochloric acid. Write the equation.