1 84 AGRICULTURAL CHEMISTRY 



with water from which the starch slowly settles. In the 

 arts, starch is used in many ways. As a food, it is used 

 mainly in its original form associated with the other or- 

 ganic compounds with which it is found in plants. 



238. Food Value of Starch. Starch is a valuable nu- 

 trient, and when digested produces heat and energy. 

 When burned in the bomb calorimeter i pound of 

 digestible starch produces 1860 calories. A calorie 

 is the unit employed for measuring heat, and is 

 the amount of heat required to raise i kilo of water i C., 

 or approximately i pound of water 4 F. One gram 

 of starch yields 4. 2 calories. Pure starch alone is inca- 

 pable of sustaining life because it contains no combined 

 nitrogen, and does not supply any material for repairing 

 the tissues of the body or for the construction of new 

 nitrogenous tissue. When associated with nitrogenous 

 compounds, starch can be used by the body for the pro- 

 duction of fat as well as for the production of heat 

 and energy. 



239. Amount of Starch in Plants. In grains, the 

 amount of pure starch ranges from 50 to 75 per cent, of 



I the dry weight of the material ; in hay and forage crops, 

 it is small, usually less than 2 per cent. The amount of 

 pure starch in some of the cereals and farm crops is ap- 

 proximately as follows : 



Pure starch. 

 Per cent. 



Wheat 68 



Wheat flour 72 



Oats 55 



Corn 75 



