20 LABORATORY EXERCISES. 



aside in a warm dry place. Weigh each 

 day, and record results for each potato 

 in tabular form as above. 

 2. What is one use of the peel of potato? 



9. TO TEST FOODS FOR STARCH. 



Materials : Corn-starch, grape-sugar, white of egg, mutton tallow, 

 various food materials, water; iodine solution;* small butter-plate, 

 test-tubes, glass jar, alcohol-lamp. 



A. Method of applying iodine test. 



Put a small amount of corn-starch in a test- 

 tube, add water and shake the mixture. 



1. Does the starch dissolve? How do you 



know? (Let the mixture stand.) 



2. Boil the mixture. 



a. What change do you notice? 



b. Has the starch dissolved? (Place 



some sugar and water in another 

 test-tube, boil, and compare with 

 the boiled starch.) 



3. Pour a little of the starch paste into a test- 



tube, add a drop of iodine,* shake, and 

 record result. 



4. Add a few drops of the starch mixture to a 



large glassful of water ; stir in a few drops 

 of iodine. What is the result? 



* A quart (1000 cc.) of iodine solution is made by dissolving in 5 

 teaspoonfuls (40 cc.) of water, one-half teaspoonful (4 grams) of 

 potassium iodide, and one-fourth this amount of iodine (1 gram). 

 This solution, when thoroughly mixed, should be diluted to make 

 one quart (1000 cc.). In a clean bottle this mixture will keep lit- 

 definitely. 



