THE LECITHINS. 65 



luminous flame. On heating, especially in the presence of potassium 

 bisulphate, they are decomposed with the formation of highly irritat- 

 ing 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 through the influence 

 of superheated steam, as also through certain ferments, the fats are 

 decomposed into glycerin and their respective acids. This decom- 

 position is spoken of as saponification, and the alkaline salts of the 

 resulting fatty acids are accordingly 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, but, 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 so-called lecithins and choleste- 

 rins. The latter were formerly regarded as essential food-stuffs ; 

 and although this view has been proved erroneous, they are never- 

 theless considered in this connection. Some of the lecithins, on the 

 other hand, possess a distinct nutritive value. 



THE LECITHINS. 



The lecithins are ethereal compounds which result from the union 

 of cholin with glycerin-phosphoric acid, in which the two 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 hydroxyl groups have been replaced by fatty acid radicles.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 .0 PO(OH) 2 



Glycerin. Glycerin-phosphoric acid. 



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

 CH.OH + 2C 17 H 35 .COOH:= CH.O.C^H^O + 2H 2 O 



CH 2 .O PO(OH) 2 CH 2 .0-PO(OH) 2 



Di-stearyl-glycerin-phosphoric 

 acid. 



