PROPERTIES OF LECITHINS 47 



and oxygen. According as they contain one or two atoms 

 of phosphorus in their molecules, they are classed as mono- 

 or di-phosphatides. The lecithins, like the fats, are esters of 

 glycerol with higher fatty acids, such as palmitic, stearic, and 

 oleic acids, but they differ from the fats in being at the same 

 time esters of phosphoric acid, as is shown by the following 

 formula of lecithin from egg yolk : 



CHO- 



CH 2 -O-P(OH)-OCH 2 CH 2 N(CH 3 ) S OH 



II 

 O 



Lecithin is readily hydrolysed by boiling with alkalis, 

 notably baryta, and is also broken up by lipase, and, less 

 readily, by mineral acids. The products of its hydrolysis are 

 glycero-phosphoric acid : 



CH 2 OHCHOHCH a OP = (OH) 2 



II 

 O 



choline HON(CH 3 ) 3 CH 2 CH 2 OH and fatty acids ; a similar 

 hydrolysis takes place in the germinating seed.* 



Originally it was considered that the fatty acids of lecithin 

 were either stearic, palmitic, or oleic, but it has been found 

 that the iodine values of the acids obtained from lecithin are 

 much higher than would be given by these acids alone. 



CHOLINE. 



To examine the products of the hydrolysis of lecithin, this 

 substance is heated with a solution of barium hydrate in ex- 

 cess ; a baryta soap is formed, which may be filtered off. The 

 aqueous solution contains barium glycero-phosphate and cho- 

 line; the latter may be extracted as follows. j- 



Treat the solution with a stream of carbon dioxide until no 

 more barium carbonate comes down. Filter and evaporate 

 the filtrate to dryness. Treat the residue with absolute alcohol, 

 which will dissolve the choline but not the barium glycero- 

 phosphate. The alcoholic solution, if treated with an alcoholic 



*Schulze: " Z. physiol. Chem.," 1887, n, 365; Schulze and Frankfurt: 

 " Ber. deut. chem. Gesells.," 1893, 26, 2151. 



t Leathes : " The Fats," " Monographs of Biochemistry," London, 1910. 



