FATS AND OILS 79 



They are abundant in many animal and vegetable 

 tissues, generally in the form of round liquid globules. 

 They are present in stems and leaves, in flax seeds and 

 the seeds of rape, cotton, and other plants, where they 

 are reserves of food for use in the early nutrition of the 

 seedling. Milk contains a considerable amount of fat ; it 

 is also found stored up in the animal body, and is re- 

 absorbed into the blood when occasion requires, its 

 oxidation assisting in the maintenance of the body 

 temperature. 



Fats and oils, as usually found in nature, are not 

 single pure substances, but mixtures of several chemical 

 compounds termed glycerides, which are formed by the 

 union of glycerin with a fatty acid ; e.g. 



C 3 H 5 (OH) 3 + 3 C,H 7 C0 2 H = C 3 H 5 (C 3 H 7 C0 2 ) 3 + sH 2 O 



glycerin butyric acid butyrin 



(a fatty acid) (a fat) 



These compounds are chemically analogous to salts, and 

 are spoken of as ethereal salts of glycerin, the glycerin in 

 them playing the part of a base. 



When treated with caustic soda or potash, the alkalis 

 turn out or set free the glycerin, and unite with the fatty 

 acid to form soaps, which are potassium or sodium salts 

 of the fatty acids ; e.g. 



C 3 H 6 (C 15 H 31 C0 2 ) 3 + 3 KOH = C 3 H 5 (OH) 3 + 3 C 15 H 31 CO 2 K 



Palmitin caustic glycerin potassium palmitate 



(a fat) potash (a potash soap) 



Such chemical action is termed saponification. 



In many seeds and other parts of plants, as well as in 

 the secretions of the pancreas in animals, an enzyme 

 named lipase occurs, which has the power of decom- 

 posing fats ; the change is a hydrolytic process, the fats 



