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the limewater in B (?). Examine a drop of the mixture in A under the microscopes for yeast cells (see Fig. 135 of text).

b. Properties of alcohol. Pour a few drops of alcohol into an evaporating-dish, ignite, and note the characteristics of the flame.

Determine whether alcohol is a good solvent for (1) sugar; (2) salt; (3) starch; (4) oils, such as cottonseed oil (?). Does alcohol mix with

water in all proportions? Repeat these experiments, using methyl alcohol (?).

c. 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 so

dium hydroxide, one

A

FIG. 47

B

C

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 (p. 302 of text), 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.)

d. After the molasses in experiment a has fermented divide the liquid in A (Fig. 47) so that each student or group of students will have from 150 to 200 cc. Pour the liquid into a flask and distill over 3 or 4 cc. (Exercise 13). Dip the end of a glass rod in the distillate and touch it to the edge of a flame (?). Test the remainder of the distillate for alcohol as in c, above.

EXERCISE 56

THE PREPARATION OF A SIMPLE ESTER

Apparatus. 250-cc. flask; ring stand and burner; test tube.
Materials. Acetic acid (R.S.); alcohol (R.S.); sulfuric acid.

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2

2

Preparation of ethyl acetate. What is an ester? Ethyl acetate is an ester derived from acetic acid by replacing an atom of hydrogen in the acid by the univalent radical ethyl (CH) and has the formula CH, CH2O. It is a colorless liquid boiling at 78° and having a characteristic fragrant odor. Pour into a small flask 10 cc. of acetic acid (or of a saturated solution of sodium acetate), 5 cc. of sulfuric acid, and 3 cc. of alcohol. Mix well and heat slightly. Ethyl acetate is formed and may be recognized by its odor. Do not mistake the odor of the vapor of alcohol for that of ethyl acetate (warm a little alcohol in a test tube and note the difference between its odor and that of ethyl acetate). The equation for the reaction is

H.C2H2O2+C2H ̧OH- →CH•C,H,O,+H,O

2 3 2

2 5

2 5

2

2

2

The sulfuric acid is added to absorb the water formed. This reaction serves as a test for both acetic acid and acetates.

EXERCISE 57

PHOSPHORUS AND ITS COMPOUNDS

Apparatus. 250-cc. wide-mouthed bottle; deflagrating-spoon; glass plate; small beaker; porcelain crucible; burner.

Materials. 0.5 cc. phosphorus trichloride; phosphorus (size of a pea); litmus paper (red and blue); 10 cc. ammonium molybdate solution (R.S.); ammonium hydroxide; nitric acid; silver nitrate solution (R. S.); 2 g. disodium phosphate.

a. Pour into a test tube about 0.5 cc. of phosphorus trichloride (hood) and add a little water, a drop at a time. Mix the liquids by shaking the tube. What gas is evolved (R)? Finally add about 5 cc. of water, pour the liquid into an evaporating-dish, and evaporate to a sirupy mass. Dilute this with a little water; transfer the solution to a test tube and add a few drops of a solution of silver nitrate. Boil the resulting mixture; finely divided metallic silver (black) precipitates. Explain.

b. Cover the bottom of a wide-mouthed bottle (250-cc.) with water to a depth of about 1 cm. Place a 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 phosphorus ceases to burn, withdraw the spoon and allow the fumes in the bottle to dissolve in the water. Test the solution with litmus paper. What is present in the water?

Pour the solution 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. Note the result (the compound formed has a

very complex composition). Add ammonium hydroxide to the mixture until the liquid is alkaline. Note the result. Again acidify the liquid with nitric acid. Note the result. The formation of a yellow precipitate upon the addition of ammonium molybdate, which precipitate is insoluble in nitric acid and soluble in ammonium hydroxide, serves as a good test for phosphoric acid and its salts.

c. Apply a gentle heat to 1 or 2 g. of disodium phosphate placed in a porcelain crucible. Gradually increase the heat to the full extent and continue the heating for about 10 minutes. When cool, dissolve the product in water and test the solution with silver nitrate solution. Compare with the product obtained by adding silver nitrate to disodium phosphate which has not been heated. Note the results. (The silver salts of the acids present are formed (pp. 353, 354 of text).)

EXERCISE 58

ARSENIC AND SOME OF ITS COMPOUNDS

Apparatus. Blowpipe; piece of charcoal (2 cm. × 8 cm.); hardglass tube (10 cm. long and 6 or 7 mm. wide); file; burner.

Materials. Arsenic (size of a grain of wheat); 0.1 g. arsenious

oxide.

a. Note the physical properties of arsenic. Place a bit of the arsenic in a cavity on a piece of charcoal and gently heat it (hɔod), using a blowpipe. Note the peculiar, garliclike odor (poisonous).

b. Introduce into a hard-glass tube an amount of arsenious oxide equal in bulk to a grain of wheat. Cover this to a depth of 2 or 3 cm. with somewhat finely powdered charcoal which has been previously heated to a high temperature in a porcelain crucible. See that the inner surface of the tube above the charcoal is perfectly clean.

Incline the tube and heat the upper portion of the charcoal to a high temperature, 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 be kept as cool as possible. The arsenious oxide is changed into a vapor, which passes over the hot charcoal. Account for the result (R).

Cut the tube as near the bottom as possible and remove the charcoal; then, inclining the tube, apply a very gentle heat to that portion of it which contains the coating. Note that small white crystals are slowly deposited in the colder portions of the tube (R). Examine these with a magnifying glass. Note their form.

* c. Marsh's test — perform in hood, as the arsine formed is poisonous. Arrange an apparatus according to Fig. 22, substituting for the tube D a clean, hard-glass tube about 30 cm. long and 8 mm. in diameter, drawn out to a jet at the end. (Use the blast lamp in making the jet.) Generate hydrogen by the usual method, and, after taking the general precautions, ignite it as it escapes from the glass jet. Sufficient acid is added from time to time to cause a gentle evolution of the gas. Now apply a strong heat to the hardglass tube at a place near its center, using the "wing-top' burner. After a few minutes note whether any deposit forms just beyond the heated portion of the tube. If none forms, the materials are free from arsenic. Now add two drops of a dilute hydrochloric acid solution of arsenious oxide (made by dissolving a bit of the oxide no larger than a pinhead in 1 cc. of the dilute acid) to the generator, rinsing it down the funnel tube with a little water. Continue the heating of the hard-glass tube at the same place. Note the deposit formed on the sides of the tube. Withdraw the heat and hold the lid of a porcelain crucible in the flame. A black deposit of arsenic forms. Cut the tube containing the deposit so as just to remove the jet and, inclining it, apply a gentle heat, as in b. Account for the results and write the equations for all the reactions involved in the experiment.

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