Note the time required for its complete evaporation. Repeat the experiment, using 10 drops of kerosene. Which of the two substances is the more volatile?

d. Pour 2 or 3 drops of gasoline into a warm 250-cc. wide-mouthed bottle. Cork the bottle and shake it vigorously. Now remove the cork and, standing at arm's length, bring a lighted splint to the mouth of the bottle (?). What use is suggested by the property noted in this experiment?

e. Compare benzene with low-boiling gasoline (benzine) in odor, solubility in water (test by adding 3 drops to 5 cc. of water and shaking), and inflammability. Are both good solvents for fats (test with 3 or 4 drops of cottonseed oil)? What advantage has carbon tetrachloride over benzene and benzine as a fat solvent?

f. Study the properties of paraffin. Is it soluble in water? in kerosene? Will it melt at the temperature of boiling water? Will it burn? Test the action of acids and alkalies on paraffin by adding a few drops of each to a bit of the paraffin on a watch glass. What properties are suggested by the term "paraffin" (see derivation of word)?

EXERCISE 52

A STUDY OF THE FLAME

Apparatus. Burner; wire gauze; porcelain dish; glass tube 15 cm. long.

Materials. Charcoal (size of a bean); 5 cc. limewater (R. S.) ; candle; wooden splint.

a. Note and account for the difference between the combustion of a wooden splint and that of a piece of charcoal. What are the conditions necessary for the production of a flame? Light a candle and place it so that the flame is against a black background and is not disturbed by air drafts; then note the different cones in the flame. Test the relative

temperatures of different parts of the flame by means of narrow strips of splints. Draw a diagram showing the different parts of the flame. Extinguish the candle flame and hold a lighted splint 2 or 3 cm. from the wick in the little column of smoke (?).

b. What two elements constitute the main parts of ordinary fuels? What products form when these elements burn in air or oxygen? Devise simple experiments to show the presence of these products in the gases evolved by the burning candle.

c. 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. Ex

plain. Press a piece of wire gauze halfway down on a Bunsen flame. Notice that the flame does not extend

above the gauze. Is this due to the absence there of combustible gases? Test for their presence by means of

a lighted splint.

FIG. 46

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. How does the miner's safety lamp prevent explosions?

Hold a porcelain dish in a small luminous Bunsen flame. Account for the deposition of carbon (lampblack). Does the nonluminous flame deposit carbon? To what is the luminosity of the flame due?

d. Recall the experiment on the Bunsen flame in Exercise 2. That the center of the base of the Bunsen flame contains the unburned gas may be shown by holding in it the end of an inclined glass tube (Fig. 46) and igniting the gas at the upper end of the tube.

EXERCISE 53

THE SUGARS

Apparatus. 3 test tubes; 2 small beakers; stirring-rod; burner. Materials. 3.5 g. copper sulfate crystals dissolved in 50 cc. water (label this solution "A"); 17.5 g. sodium potassium tartrate (Rochelle salts) dissolved in 50 cc. sodium hydroxide solution (label this solution "B"; solutions A and B should be poured into bottles and reserved for future exercises); 5 cc. commercial glucose or Karo corn sirup; 2 g. sucrose; 1 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.

a. The test for dextrose. The most common test for dextrose is the reaction with Fehling's solution. This is prepared as needed by mixing equal volumes of solutions A and B, prepared as directed above.

Pour into a test tube about 3 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 boiling, add 1 or 2 drops of commercial glucose (Karo corn sirup will do as well), and continue the heating for a few moments. The copper sulfate in the solution 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.

b. The action of cane sugar on Fehling's solution. In a similar way try the action of pure cane sugar on Fehling's solution (?).

Now dissolve about 1 g. of the sugar in 10 cc. of water. Add 4 or 5 drops of concentrated hydrochloric acid and slowly heat nearly to boiling. Set the solution aside for about five minutes, then cool and neutralize the acid present by

adding a concentrated solution of sodium carbonate until the resulting mixture is just alkaline to litmus paper. Now test this with Fehling's solution as in a. Account for the result.

EXERCISE 54

A STUDY OF STARCH

(Students interested in the subject of foods should perform the additional exercises included under Appendix A.)

Apparatus. Microscope; 200-cc. beaker; stirring-rod; ring stand and burner; 3 test tubes.

Materials. Iodine solution prepared by dissolving 0.5 g. iodine and 2.5 g. potassium iodide in 25 cc. water (label this "Iodine Solution" and preserve for use in a number of exercises); 0.1 g. flour; 10 g. 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.

a. Microscopic appearance. Examine under the microscope the appearance of starch from different sources (corn, wheat) when magnified. Draw diagrams of the starch granules.

b. Actions of acids on starch. Try the action of starch solution on Fehling's solution (as in Exercise 53) (?).

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 25 cc. Cool the liquid, neutralize with sodium carbonate, and again test the solution with Fehling's solution (?).

c. Test for starch. Recall the action of iodine on starch (Exercise 47). This constitutes a good test for starch.

Test different foods (such as bread, potatoes, and corn meal) for starch. To do this, boil from 5 to 10 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 (?).

*d. 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, 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. This is sweet and dissolves in water, forming a mucilagelike solution which is used on the back of postage stamps and for other similar purposes.

EXERCISE 55

THE PREPARATION AND PROPERTIES OF COMMON ALCOHOL (ETHYL ALCOHOL)

Apparatus. One 2000-cc. flask (or bottle) connected with tube and bottle, as shown in Fig. 47; test tube; stirring-rod; apparatus shown in Fig. 26; evaporating-dish.

Materials. 200 g. molasses or Karo corn sirup; cake of yeast; 50 cc. limewater (R. S.); 25 cc. alcohol; 15 cc. methyl alcohol; small amounts (size of a pea) of sugar, starch, salt; 1 cc. cottonseed oil; iodine solution prepared in Exercise 54; sodium hydroxide solution; soda lime sufficient to fill tube C (Fig. 47).

a. Preparation of alcohol. (It is suggested that this experiment be performed by the instructor or by students selected by the instructor; after the alcohol is generated the liquid may be divided among the different members of the class who will then test for the alcohol as directed in d.)

Dissolve about 200 g. of ordinary molasses in 2000 cc. of water in the flask A (Fig. 47). 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 lime). Set the apparatus aside in a warm place (30° is best) for one or two days. Note that a gas is evolved in A and bubbles through