FOODS 301 



test tube, and strong nitric acid is added. The mixture 

 is heated, and if protein is present the food changes to. 

 a yellow color. If then the acid is poured off, and 

 strong ammonia added, the yellow color changes 

 to a deep orange, and we may be sure protein is 

 present. 



Carbohydrates. In this class are included starches 

 and sugars. The carbohydrates are composed of three 

 elements : carbon, hydrogen, and oxygen. These are so 

 combined that there is always twice as much 

 hydrogen as oxygen. For example, the formula 

 for common sugar is C 12 H 22 llf for grape sugar 

 C 6 H 12 6 , and for starch C 6 H 10 5 . 



Starch. Starch is formed in all green plants. Fre- 

 quently it is stored in the cells of grain, in seeds, and 

 especially in stems and roots. We obtain much of our 

 starch from potatoes and bread. 



Test for starch. Starch when treated with a solu- 

 tion of iodine turns dark blue. This is the test usually 

 employed to detect the presence of starch. 



Sugar. Sugar is likewise derived from plants. There 

 are many different kinds of sugar; for example, cane 

 sugar, grape sugar, and milk sugar. These substances 

 differ more or less in chemical composition. However, 

 both cane and milk sugar may be changed into grape 

 sugar by boiling them with hydrochloric acid. 



Test for sugar. In the test most commonly used to 

 detect the presence of sugar, a mixture called Fehling's 

 solution is used. If a few drops of this solution are 



