FOODS AND FOOD TESTS 111 



EXERCISE 101 

 FOODS AND FOOD TESTS 



Apparatus and Materials. Potato, kitchen grater, laundry starch, 

 measuring cup, flour, cheesecloth, test tube or beaker, grape sugar, 

 Fehling's solution (see Introduction), raisin, granulated sugar, hydro- 

 chloric acid, white of egg, nitric acid, ammonia water, white woolen 

 yarn, white cheese or sour milk, ground peanuts. 



a. Starch. Peel a potato, grate it fine, and stir it with water. 

 The starch will thus be separated from the other material, 

 such as cellulose, and will tend to settle to the bottom. If you 

 then pour off the water and the lighter sediment, the starch 

 will remain. Pour the starch upon a filter paper or a piece of 

 newspaper, and let it dry. 



Note the "crunchy" feeling of some laundry starch when you 

 crush it between your fingers. 



Boil about ^ of a teaspoonful of powdered starch in your 

 measuring cup with % of a cupful of water. Let the mixture 

 cool; it should "set" to a thick paste. Review Exercise 89, c. 



b. Gluten. Out of % of a cupful of flour and a little water 

 make a tough dough. Tie the dough in a piece of good cheese- 

 cloth, and knead the dough under water. Note that the 

 starch comes through the cloth. When no more starch can be 

 kneaded out of the dough, examine the impure gluten that 

 remains. Give its color. Is it sticky? Elastic? 



c. Grape Sugar. Into a test tube or small beaker put a 

 pinch of grape sugar; dissolve it in the least possible amount of 

 hot water. Add to the solution about 3 cu. cm. of Fehling's 

 solution, and boil the mixture. What is the result? This 

 serves as a test for grape sugar. Taste a little of the grape sugar. 



Crush a raisin, soak it in water, and boil the solution with 

 Fehling's solution. Is grape sugar present? 



Dissolve a pinch of granulated sugar in the least possible 

 amount of water, and boil with Fehling's solution. Result? 



