CHEMIC COMPOSITION OF THE HUMAN BODY. 15 



stearin, etc. The reaction which takes place in the combination of 

 glycerin and the acid is expressed in the following equation : 



C 3 H 5 (HO) 3 + (HC 1S H3 5 2 ) 3 = C 3 H 5 (C 1S H3 5 2 ) 3 + 3H 2 0. 

 Glycerin. Stearic Acid. Stearin. Water. 



Hence, strictly speaking, the fats are compound ethers, in which 

 the hydrogen of the organic acid is replaced by the trivalent radicle, 

 tritenyl, C 3 H 5 . 



Stearin, C 3 H 5 (C 1S H^O^, is the chief constituent of the more solid 

 fats. It is solid at ordinary temperatures, melting at 55 C., then 

 solidifying again as the temperature rises, until at 71 C. it melts 

 permanently. It crystallizes in square tables. 



Palmitin, C 3 H 5 (C 1C H 31 O 2 ) 3 , is a semifluid fat, solid at 45 C. and 

 melting at 62 C. It crystallizes in fine needles, and is soluble in 

 ether. 



Olein, C 3 H 5 (C 1S H 33 O 2 ) 3 , is a colorless, transparent fluid, liquid at 

 ordinary temperatures, only solidifying at o C. It possesses marked 

 solvent powers, and holds stearin and palmitin in solution at the tem- 

 perature of the body. 



Saponification. When subjected to the action of superheated 

 steam, a neutral fat is saponified *'. e., decomposed into glycerin and 

 the particular acid indicated by the name of the fat used : e. g., 

 stearic, palmitic, or oleic. The reaction is expressed as follows : 



C 3 H 5 (C 18 H 33 2 ) 3 + 3 H 2 = C 3 H 5 (HO) 3 + 3(C U H M O 2 ). 

 Olein. Water. Glycerin. Oleic Acid. 



The fatty acids thus obtained are characterized by certain chemic 

 features, as follows : 



Stearic acid is a firm, white solid, fusible at 69 C. It is soluble 

 in ether and alcohol, but not in water. 



Palmitic acid occurs in the form of white, glistening scales or 

 needles, melting at 62 C. 



Oleic acid is a clear, colorless liquid, tasteless and odorless when 

 pure. It crystallizes in white needles at o C. 



If this saponification take place in the presence of an alkali, e. g., 



