LECITHIN 53 



of phosphate by ammonium molybdate. The classification of 

 the Hpins is based upon their nitrogen and phosphorus content 

 as follows : — 



A. Phospholipins which contain both phosphorus and 

 nitrogen. According to the number of atoms of phosphorus, 

 one or two, contained in their molecule, they are classed as 

 mono- or di-phosphatides. To this group belong lecithin and 

 kephalin. 



B. Galactolipins or Cerebrosides which contain nitrogen 

 but no phosphorus and yield on hydrolysis galactose in addition 

 to fatty acids and glycerol. 



A. PHOSPHOLIPINS. 



LECITHIN. 



Although widely distributed in the vegetable kingdom 

 lecithin usually occurs together with other lipins and in rela- 

 tively small amount ; for this reason the most convenient 

 source for the preparation of lecithin is egg yolk. This sub- 

 stance is extracted with five times its volume of 96 per cent 

 alcohol ; the extract is then cooled to 0°, filtered and pre- 

 cipitated 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 con- 

 centrated solution of ammonium carbonate until all the cad- 

 mium is thrown out of solution ; the solution is filtered whilst 

 hot and on cooling the filtrate to 10° the lecithin is deposited. 

 It may be purified by dissolving in chloroform and precipi- 

 tating from solution by the addition of acetone in which 

 lecithin is insoluble. 



The following are some of the more characteristic re- 

 actions of lecithin : — 



1. If to an alcoholic solution of lecithin an alcoholic 

 solution of cadmium chloride be added, a white precipitate 

 of the cadmium chloride double salt is formed. 



2. If a little lecithin is boiled with caustic soda, trimethyl- 

 amine is formed, and may be identified by its characteristic 



