ORGANIC COMPOUNDS OF PLANTS 



185 



Pure starch. 

 Per cent. 



Rice 78 



Potatoes 80 



Wheat bran 8 



Straw less than I 



Hay i to 3 



Experiment 46. Preparation of potato starch. Reduce one or 

 two clean potatoes to pulp on the grater. Tie the pulp in a clean 

 cloth and squeeze into a large cylinder filled with water, occa- 

 sionally dipping the bag into the water. Allow the cylinder to 



Fig. 76. Obtaining starch from potato. 



stand for twenty minutes, or until the starch has all settled ; pour 

 off the water. If the starch is not clean, wash by adding more 

 water, and allow it to settle again ; then pour off the water. 

 Leave the cylinder in the desk until the starch is dry. Save this 

 starch for the following tests : 



Tests for starch. Place 0.5 gram of starch in a test-tube about 

 one-half full of water. Shake the test-tube, boil, and filter ; then 

 to this filtrate add a few drops of iodin. 



Questions, (i) What was the difference in the action of hot an 



