THE FATS 97 



Similarly the triatomic alcohol glycerol may be combined with the 

 higher fatty acids to form the true fats. 



CH 2 OH CH 2 -OOCC 15 H 31 



CHOH + 3 C 15 H 31 COOH = CH- OOCC 15 H 31 + 3H 2 O 



CH 2 OH CH 2 - OOCCi 5 H 31 



Glycerol Palmitic acid Tri-palmitin 



The animal fats are for the most part mixtures of tri-palmitin, tri-stearin, 

 and tri-olein, the last two being esters of glycerol with stearic acid, C 17 H 35 

 COOH, and the unsaturated oleic acid, C 17 H 33 COOH. Human fat con- 

 sists of a mixture of which tri-palmitin and tri-stearin comprise three-fourths 

 of the whole. The fat in milk and butter is in part tri-butyrin, the ester 

 of glycerol with butyric acid,C 2 H 5 COOH. The percentage of any in- 

 dividual fat in animal tissue depends on, and is characteristic of, the particular 

 species of animal from which the fat was obtained. Ordinary mutton fat 

 contains more tri-stearin and less tri-olein than pork fat, and the mutton 

 fat is stiffer because the melting-point of the tri-stearin is the highest of 

 the fats. 



The pure fats are odorless, tasteless, and generally colorless. They 

 are insoluble in water and cold alcohol, but are dissolved by acetone, hot 

 alcohol, benzol, chloroform, and ether. When shaken with water, protein 

 solutions, soap, or gum arabic, the fats assume a finely divided condition 

 known as an emulsion. The suspension in water is only temporary, while 

 the emulsions are permanent. 



The fats are hydrolyzed or saponified by superheated steam into glycerol 

 and the fatty acids, the reaction being the reverse of that indicated in the 

 equation above. On boiling with caustic alkalies, they are similarly saponi- 

 fied; the fatty acids are then combined with the bases to form salts or soaps. 



Lecithins are tri-glycerides in which the H atom of two instead of three 

 groups of the glycerol is replaced by a fatty acid radical; for the H of the 

 third hydroxyl (OH) group there is substituted an ester-like combination 

 of phosphoric acid with a nitrogen-containing organic base, choline. 



CH 2 OOCC 17 H 35 



CHOOCC 17 H 35 C 2 H 4 OH 



I / ' 



CH 2 O - O P - O C 2 H 4 N=(CH 3 ) 3 



\ \ 



(CH 3 ) 3 =N OH 



OH 



HO 



Lecithin Choline 



