APPENDIX A

SOME OPTIONAL EXERCISES OF SPECIAL INTEREST TO STUDENTS OF HOME ECONOMICS

EXERCISE 90

A STUDY OF TEXTILE FIBERS

Apparatus. 4 small beakers or test tubes; stirring-rod; burner; evaporating-dish; 2 large beakers; microscope.

Materials. 3 strips each of uncolored cotton, wool, silk, and linen cloth (3 cm. × 15 cm.); 50 cc. of sodium hydroxide solution; strip of filter paper; 3 strips of filter paper (2 cm. x 10 cm.); ammonium hydroxide; hydrochloric acid; sulfuric acid.

a. Effect of heat upon textile fibers. Ignite the end of a strip of cotton cloth in a Bunsen flame; then withdraw from the flame. Note the odor of the burning cloth. Does the cloth when ignited continue to burn?

Repeat, using strips of wool, silk, and linen. Can you distinguish in this way between vegetable fibers (cotton, linen) and animal fibers (wool, silk)?

b. How to distinguish between vegetable fibers (cotton, linen) and animal fibers (wool, silk). Place a strip of each kind of cloth in small beakers, cover the cloth with sodium hydroxide solution, and boil the liquid for ten minutes, replacing the water as it evaporates (the cloth must always be completely covered with the liquid); then set the beakers aside until cool (?).

c. How to distinguish between the animal fibers. Immerse strips of silk and wool in concentrated hydrochloric acid and note the change after they have stood a few minutes (?).

d. How to distinguish between the vegetable fibers. Immerse strips of cotton and linen in concentrated sulfuric acid for two minutes (?).

e. Microscopic appearance of textile fibers. Examine the appearance of each kind of fiber under the microscope. Compare with the diagrams on page 330 of text.

f. Parchment paper. Pour 20 cc. of sulfuric acid slowly (CAUTION), and with constant stirring, into a beaker containing 10 cc. of water. Pour the solution into an evaporatingdish and allow to cool. Draw strips of filter paper slowly through the acid and then immerse them in a large beaker of water. Finally, wash the strips in a large beaker of water containing 2 or 3 drops of ammonium hydroxide.

When the strips are dry, compare their properties with those of the untreated paper.

EXERCISE 91

THE DETERMINATION OF THE AMOUNT OF ALCOHOL PRESENT IN AN ALCOHOLIC LIQUID (QUANTITATIVE)

Apparatus. Flask and condenser connected as is shown in Fig. 49 (A is a 250-cc. flask, and C a flask which holds 100 cc. when filled to a point marked on its neck (a graduated cylinder may be used in its place)); ring stand and burner; hydrometer reading from 0.900 to 1.000; cylinder.

Materials. 100 cc. of any alcoholic liquid, such as an alcoholic medicine.

The method commonly used is based on the fact that the specific gravity of an aqueous solution of alcohol varies according to the percentage of alcohol present. Tables have been worked out with great care, giving the specific gravities of solutions of alcohol of various strengths. If we know the specific gravity of an aqueous solution of alcohol, therefore, it is only necessary to refer to the table and read the percentage of alcohol. These tables are calculated for certain

temperatures, so that in determining the specific gravity of the alcohol care must be taken that the temperature of the solution is the same as that indicated in the tables used. These tables are given in Allyn's "Elementary Applied Chemistry" (pp. 66-75); also in Bulletin 107, United States Department of Agriculture;

also in the "United States Pharmacopoeia" used by the druggist.

Pour exactly 100 cc. of any alcoholic liquid into a flask A (Fig. 49) and distill over about 50 cc., collecting the distillate in the 100-cc. flask, as shown in the figure. Since alcohol is quite volatile (boiling point 78.3°), all of the alcohol present in the 100 cc. of liquid will be contained in the 50 cc. of the distillate. Now dilute the distillate to exactly

FIG. 49

B

100 cc., mix thoroughly, pour into a cylinder, and having brought it to the proper temperature, determine its specific gravity by means of a hydrometer. Refer to the tables for the percentage of alcohol present in the distillate. Why is it necessary to distill the liquid? Why dilute the distillate to 100 cc. before taking the specific gravity?

EXERCISE 92

THE EFFECT OF PRESERVATIVES

Apparatus. Two 250-cc. bottles or beakers; 500-cc. beaker; 2 test tubes; ring stand and burner.

Materials. 300 cc. sweet milk; drop of formalin; 10 cc. hydrochloric acid to which is added 1 drop of a solution of ferric chloride (R. S.) ; 1 g. sodium benzoate.

a. The effect of formaldehyde on milk. Thoroughly clean two small bottles with hot water and half fill each with sweet milk. Add to the milk in one of the bottles a drop of formalin and mix thoroughly. Now pour about 5 cc. of milk from each of the two bottles into separate test tubes; add to each an equal volume of concentrated hydrochloric acid to which has been added just a trace of ferric chloride solution (the ordinary commercial hydrochloric acid serves the purpose well, since it usually contains a trace of ferric chloride as an impurity).

Mix the contents of each of the tubes thoroughly and set them in a beaker of boiling water. Note any change in color. How can you detect the presence of formaldehyde in milk?

Set the two bottles containing the remainder of the milk aside and examine from time to time, noting when the milk in each becomes sour.

b. The effect of sodium benzoate on sweet cider or grape juice. The student may likewise study the action of sodium benzoate in preventing the fermentation of sweet cider or grape juice. In such cases the weight of the preservative added to the beverage should be from 0.1 to 0.2 per cent of the weight of the beverage.

The use of formaldehyde in foods is no longer permitted by the Federal laws, since it is a poison. The use of sodium