46 FATS, OILS, AND WAXES 



The approximate amount of lecithin contained in various 

 substances may be seen from the following table : 



Egg yolk 9*4 per cent 



Liver 2'i ,, 



Blood 1-8 



Leguminous seeds .... o'8-i'64 per cent 



Cereals 0*25-0-53 ,, 



Botanically, the term lecithin is generic, and plant products so 

 called have not yet been obtained in a pure state and contain 

 other substances of a similar nature. 



PREPARATION. 



The most convenient source for the preparation of lecithin 

 is egg yolk. This substance is extracted with five times its 

 volume of 96 per cent alcohol ; the extract is then cooled 

 to o, filtered and precipitated with an alcoholic solution of 

 cadmium chloride ; the precipitated double salt is next washed 

 with alcohol and ether ; it is then decomposed by boiling with 

 eight times its quantity of 80 per cent alcohol and carefully 

 adding a concentrated solution of ammonium carbonate until 

 all the cadmium is thrown out of solution ; the solution is fil- 

 tered whilst 'hot and on cooling the filtrate to 10 the lecithin 

 is deposited. It may be purified by dissolving in chloroform 

 and precipitating from solution by the addition of acetone 

 in which lecithin is insoluble. 



Pure lecithin has not as yet been obtained from vegetable 

 sources, the substances isolated by Winterstein * and his col- 

 laborators from wheat flour and from the seeds of Avena 

 sativa, Lupinus albus, L. luteus, Vicia sativa, from the leaves of 

 <Lsculus kippocastanum, etc., being mixtures which, moreover, 

 contain a carbohydrate complex. For an account of the 

 methods employed in the extraction of these substances the 

 original papers should be consulted. Smolensky j- found that 

 wheat germs (i.e. the embryos which are a bye-product of the 

 flour mills) yielded a phosphatide whose composition was 

 much closer to that of ordinary lecithin than was that 

 obtained from the flour. 



* Winterstein andHiestand: " Zeit. physiol. Chem.," 1907, 54, 288; Winter- 

 stein and Smolensky: id., 1908, 58, 506; Winterstein and Stegmann: id., 1908, 

 58, 527. See also Schulze and Likiernik : id., 1891, 15, 405 ; Schulze : id. t 

 1895, 20, 228. 



t Smolensky : id., 1908, 58, 522. 



