X. THE OCCURRENCE OF CARBOHYDRATES IN PLANTS 



. The Test for Starch: 



Experiment 18. To ascertain the test for the presence 

 of starch. 



1. Place a bit of corn starch, about the size of a small 

 shot, into a test-tube one-fourth full of water. 

 Shake it thoroughly. Is starch soluble in cold 

 water? Give a reason for your answer? 



2. Bring the starch mixture to a boil over the flame 

 of an alcohol lamp, or Bunsen burner. Describe 

 the result. Is starch soluble in hot water? Give 

 a reason for your answer. 



3. Set this test-tube aside to cool for a moment or 

 two. 



4. Into a test-tube one-fourth full of clear water 

 place 3 or 4 drops of iodine solution, using a pipette. 

 Shake the mixture and describe the color. 



5. Now place i or 2 drops of the iodine into the 

 cooled, boiled starch mixture. Shake the mixture 

 and describe the resulting color. 



6. Pour one-half of this mixture into another test-tube 

 one-half full of water. What color appears? 



7. Describe a test for the presence of starch. (NOTE: 

 The iodine is not the test; it is only the reagent 

 used.) 



Experiment 19. To see if there is starch in (a) seeds; 

 (b) stems; (c) roots. 



40 



