HANDBOOK FOR BIO-CHEMICAL LABORATORY. 19 



acetic acid, but readily by a slight excess of hydrochloric acid, 

 especially in the presence of alcohol, They are insoluble in 

 alcohol and ether. 



Lecithin. 



Preparation. The yolk of several eggs free from white are 

 violently shaken with ether until the ether does not dissolve 

 any more. The several etheral extracts are freed from ether 

 by distillation, and the residue dissolved in petroleum ether 

 and filtered. The filtrate is transferred to a separatory funnel 

 and shaken several times with 75$ alcohol; the alcoholic ex- 

 tracts are united, and allowed to stand until entirely clear. 

 Separate any petroleum ether present, and filter. The last 

 portions of petroleum ether are distilled off, and the residue 

 is allowed to stand in a cold place for several days, when a 

 precipitate will be produced. The liquid is separated from the 

 precipitate by decantation and then filtration. Decolorize the 

 solution by boiling with animal charcoal, filter, and evaporate 

 to syrupy consistency at 50-60 0. Dissolve the syrup in 

 ether, filter, and evaporate the filtrate, when the lecithin will 

 be obtained in a nearly pure form. To further purify, dis- 

 solve in as little absolute alcohol as possible, and on cooling 

 this solution in a freezing mixture to 5 to 15 C. the 

 lecithin will be deposited. This is filtered while cold, and 

 dried in a vacuum over sulphuric acid. (E. Gilson.) 



Properties. Lecithin is a soft, waxy, mouldable, not mark- 

 edly crystalline mass, which when placed on a microscope slide 

 with water forms oily drops, appearing under the microscope 

 like worms, called "myeliue forms." It is easily decom- 

 posed by acids and alkalies, especially by the latter. On 

 fusion with soda and saltpetre on platinum foil it yields 

 a mass in which phosphoric acid can be easily detected. It 

 combines with acids and bases. The combination with HC1 

 gives a double salt with PtCl 4 , which is insoluble in alcohol, 



