38 THE ELEMENTS OF PLANT FOOD 



Gums. Knowledge of the chemistry of gums is 

 quite limited. They have the same general formula 

 as the dextrins and are products of various trees and 

 plants. The most familiar are gum arabic, wood gum, 

 and gum tragacanth. 



Nitrogen Free Extract. When a chemical analysis 

 of food is made, a portion that has no nitrogen in it, 

 non-nitrogenous, is called nitrogen free extract. It 

 consists largely of the carbohydrates other than cellu- 

 lose, which is named crude fiber. 



Fats 



Fats and oils are found in both vegetable and animal 

 bodies. They are produced from starch in plants 

 during the progress of growth. Fat is found in all 

 parts of the plant, but the mature seed has the largest 

 proportion. The seeds of flax, cotton, and corn are 

 particularly rich in fat. During germination the fat 

 in the seed changes back to starch. 



The fats and oils are salts ; that is, they are made 

 by the union of a base and acid. The base is glycerin 

 (C 3 H 5 (OH) 3 ) in its pure state a sweet, colorless, odor- 

 less liquid. The character of the fat depends upon 

 the acid that is united with the glycerin. There are 

 four acids that are most common in forming fats : 

 stearic, palmitic, oleic, and butyric. 



Notes. Stearin (C 57 H 110 O,.) is a fat made by the union of the 

 base glycerin and stearic acid. It is a solid fat and melts at a compar- 

 atively high temperature. Most of the solid animal fats, such as beef, 

 mutton, tallow, and lard, are composed largely of stearin. 



Palmitin (C^HggOg) is a solid fat with a slightly lower melting 

 point than stearin. It is a constituent of human fat, butter, and palm 

 oil. 



