76 THE FATS. 



alcohol they are insoluble. On shaking fats (containing a small 

 amount of fatty acids) with water the fat globules are finely divided, 

 resulting in the formation of an emulsion. They are non- volatile 

 and burn with a luminous flame. On heating, especially in the 

 presence of potassium bisulphate, they are decomposed with the 

 formation of highly irritating vapors of an aldehyde, acrolein, which 

 in turn results from glycerin, according to the equation : 



C 3 H 5 (OH) 3 = C 2 H 3 .CHO + 2H 2 0. 



On boiling with concentrated alkalies, or acids, or through the 

 influence of superheated steam, as also through certain ferments 

 (lipases), the fats are decomposed into glycerin and their respective 

 acids. This decomposition is spoken of as saponification ; the 

 alkaline salts of the resulting fatty acids (in the case of hydrolysis 

 with alkalies) are termed " soaps." 



On prolonged exposure to the air, even in the absence of micro- 

 organisms, the fats become rancid i. e., they become acid and assume 

 a most disagreeable odor and taste. During this process a partial 

 decomposition occurs, with the formation of glycerin and fatty 

 acids, which latter are then oxidized to certain volatile, offensive 

 smelling oxy-acids. The exact nature of the process which thus 

 takes place is not well understood ; as has been stated, it can occur 

 in the absence of micro-organisms and through the influence of light 

 and air only. 



The fats which occur in the animal body generally present a more 

 or less well-marked yellow or red color. This color is referable to 

 the presence of certain lipochromes. These are compounds which, 

 like the fats themselves, are devoid of nitrogen ; and some of them 

 apparently are hydrocarbons, of whose structural composition, how- 

 ever, nothing is known. 



Closely related to the fats are the lecithins and cholesterins. 



THE LECITHINS. 



The lecithins are esters which result through the union of cholin 

 with glycerin-phosphoric acid, in which the two remaining glycerin 

 hydroxyl groups have been replaced by fatty acid radicles. This 

 union takes place according to the equations : 



(1) CH 2 .OH CH 2 .OH 

 CH.OH -f OH.PO.(OH) 2 == CH.OH + H 2 O 



CH 2 .OH CH 2 .O PO(OH) 2 



Glycerin. Glycerin-phosphoric acid. 



(2) CH 2 .OH CH 2 .O.C 18 H 35 

 CH.OH + 2C 17 H 35 .COOH= CH.O.C 18 H 35 -f 2H 2 O 



CH 2 .O PO(OH) 2 CH 2 .O PO(OH) 2 



Di-stearyl-glycerin -phosphoric 

 acid. 



