Hold the test tube over the sink. Results? Note the odor of the escaping vapors of acetaldehyde, CH,CHO. Hold in the vapors a stirring rod wet with ammoniacal silver nitrate solution. To make this, add one drop of a 10 per cent solution of caustic soda to 1 c.c. of silver nitrate solution, and then add 1 c.c. of ammonia water. The deposit on the rod is silver. Explain.

b. Put 2 c.c. of methyl alcohol, CH3OH, in a test tube supported in a ring stand or rack. Make a copper spiral by winding about a glass rod or a pencil a foot of copper wire. Remove the pencil or rod, and hold the spiral in the flame (use tongs) until it is red hot. Then drop it into the methyl alcohol. Note the sharp vapor of formaldehyde, CH2O, mixed with the vapor of the alcohol.

CH2OH+0→→→→ CH2O+H2O.

EXPERIMENT LXXXIII.

ACETIC ACID AND ACETATES.

Apparatus. Beaker (50 c.c.), test tubes, evaporating dish, stirring rod, wire gauze, ring stand.

Materials.

Commercial (concentrated and dilute) acetic acid, concentrated sulphuric acid, vinegar, sodium carbonate, litmus and filter papers, alcohol.

a. Note the taste of a drop of dilute acetic acid. Heat some to boiling in a test tube. Odor? Its action to litmus? Cf. Experiment XXIV, a and b. Test vinegar in the same ways. Results?

b. In a test tube mix 1 c.c. of concentrated acetic acid with 2 c.c. of alcohol, and add half a c.c. of concen

OTHER ORGANIC ACIDS.

115

trated sulphuric acid. Heat carefully, and describe the odor. It is that of ethyl acetate, CH3COOC2H5. The sulphuric acid removes water. Equation? If you were given a liquid suspected of being acetic acid, how would you prove it to be this substance?

c. In a 50 c.c. beaker dissolve 10 grams of sodium carbonate in 10 c.c. of water and add to it commercial acetic acid (5 c.c., or less, at a time) until the reaction is distinctly acid on stirring, and effervescence ceases. Then transfer the solution to an evaporating dish, and concentrate it over the wire gauze until a drop held on a stirring rod crystallizes when cool (cf. Experiment XXXVII, g). Set the dish aside until the next period. Name the crystals. Their shape? Filter them off, and dry them between filter papers.

d. Carefully heat some of the crystals of c in a test tube. Do they contain crystal water (cf. Experiment XVII)? Treat 1 c.c. of them, in a test tube, with 1 c.c. of concentrated sulphuric acid, and warm gently. Result? Odor? Remember to pour the concentrated acid into water when cleaning the test tube!

To 1 c.c. of the crystals add 1 c.c. alcohol and half a c.c. of concentrated sulphuric acid. Warm gently, and note the odor of the vapors. Result? Conclusion?

EXPERIMENT LXXXIV.

OTHER ORGANIC ACIDS.

Materials. Citric acid, lemon juice, oxalic acid, benzoic acid, alcohol, sodium bicarbonate, potassium permanganate solution, dilute and concentrated sulphuric acid, litmus.

a. For the properties of tartaric acid see Experiments XXIV, c; XLVII, a; LX, c; and LXI, b and c.

b. Make an aqueous solution (by heating) of 1 gram, or less, of crystallized citric acid, H3C6H5O7+H2O, and note its taste, odor, and reaction toward litmus and toward sodium bicarbonate. Repeat, using lemon juice instead of citric acid solution. Results?

c. See Experiment LXXVIII for the behavior of oxalic acid, H2C2O4, when heated. Prove the presence of crystal water in oxalic acid. To 1 c.c. of potassium permanganate solution add half a c.c. of dilute sulphuric acid and then oxalic acid solution, drop by drop. Result? Conclusion?

d. Heat 1 c.c. of benzoic acid, C.H5COOH, with 5 c.c. of water. Result? Boil for a moment. Odor of vapors? Now cool the solution under the faucet. Result? Redissoľve the benzoic acid by applying heat. Cautiously taste a drop of the solution, and note its action toward litmus and sodium bicarbonate. Results?

In a test tube heat carefully 1 c.c. of benzoic acid with 1 c.c. of alcohol until you get a solution; then add half a c.c. of concentrated sulphuric acid and heat again. Note the odor of the vapors of ethyl benzoate, C6H5COOC2H5. Pour the solution into 10 c.c. water, and note the separation of the oily ester.

EXPERIMENT LXXXV.

SOAP.

Apparatus. Tin” can, stirring rod, test tubes, ring stand.

Materials.

Sodium hydroxide, lard, fine salt, "Castile or "Ivory" soap, litmus, dilute sulphuric acid, calcium sulphate solution.

a. In a clean tin can dissolve 8 grams of sodium hydroxide in 60 c.c. cold water. If possible have the cover only partially cut out, so that it may be pushed down as a lid during the boiling. To the alkaline solution add 25 grams of lard, and heat the mixture to boiling, having the opening of the can almost closed by the lid. Be careful not to let the alkali spatter into your eyes!

After thirty minutes stop the boiling, and see if the mixture begins to become solid. (Care!) If not, continue heating until it does.

Now add to the mixture, while it is still warm, 16 grams of fine salt in lots of about 2 grams each. Stir carefully after each addition. Finally, boil the mixture for ten minutes, and let it cool. The soap will appear as a solid cake on the surface of the solution. Remove it, rinse it with a little water, and let it dry.

b. Dissolve about 1 c.c. of "Ivory" or Castile soap in 10 c.c. of water, and test the reaction of the solution with litmus. Result? Treat half of the solution with dilute sulphuric acid. Result? The solid product is a mixture of the organic acids of the soap.

Treat the other half of the soap solution with a solution of calcium sulphate. Result? Heat to boiling. The product is the calcium salt of the acids ("lime soap "). (Cf. §§ 70, 413, and 435 of text.)

EXPERIMENT LXXXVI.

CARBOHYDRATES.

Apparatus. Beaker, test tubes, ring stand, wire gauze. Materials. Fehling's solution (see a), grape sugar, cane sugar, molasses, concentrated hydrochloric acid, sodium carbonate, starch or starch paste.

a. See Experiment LXIX for the action of grape sugar with alkaline cupric salts. A better solution for testing the sugars is the one called "Fehling's Solution." Cupric sulphate crystals (34.64 grams) and 1 c.c. dilute sulphuric acid are dissolved in water, and the solution is diluted to exactly 500 c.c. This is solution I. Solution II consists of 175 grams of sodium potassium tartrate, 50 grams of sodium hydroxide, and enough water to make the volume exactly 500 c.c. These solutions are kept in separate, rubber-stoppered bottles. Equal volumes of the two are mixed just before they are used. One cubic centimeter of Fehling's solution is completely reduced by exactly 0.005 gram of grape sugar.

To 10 c.c. Fehling's solution in a beaker add a drop of a solution of grape sugar, and heat to boiling over the wire gauze. Result? Let the precipitate settle, and add another drop of grape sugar solution; repeat the process until the Fehling's solution has just lost its blue color. Calculate how much grape sugar you added.

b. In a test tube add some cane sugar solution to 5 c.c. Fehling's solution, and heat to boiling. Is there reduction? Try a solution of molasses instead of cane sugar. Result?