EXERCISE 33 



Just as the chemist has worked out tests for carbon dioxid and acids and alkalies, we have tests for 

 many of the useful substances in foods the nutrients. Among the nutrients are a class called carbo- 

 hydrates (in which we find starch and sugar), the proteins, the fats and oils, and the mineral matters 

 found in the ash after burning. 



Problem. How does iodin (the solution used for the test) affect starch ? 



What to use. Starch ; iodin solution ; test tubes ; flame. 



What to do. Place a drop of iodin solution on a piece of starch. Stir a small bit of starch in cold 

 water and pour into boiling water in a test tube ; allow to cool ; add a drop of iodin solution. 



Results. Note any changes that take place. 



Questions. 1. You have found out how iodin affects starch. What else do you need to know in 

 order to be able to use iodin as a test for starch ? 



2. Is there any starch in the cotyledon of a bean ? 



3. Is there starch in the endosperm of the corn ? 



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