THE LECITHINS. 31 



with, albuminous substances. It is found in the yelk of the 

 egg in an unstable union with vitellin. 



67. PREPARATION OF LECITHIN. In the following work the 

 student should remember that ether and petroleum-ether are very 

 inflammable. 



Separate the albumin of an egg as completely as possible from 

 the yelk. Place the yelk in a cylindrical, glass-stoppered bottle, 

 add two or three times its volume of ether, and shake the bottle 

 until they are well mixed. Allow it to stand until the ether above 

 becomes clear, and then decant the latter into a distilling flask. Re- 

 peat this extraction several times, when most of the coloring matter 

 should have been dissolved. Preserve the insoluble for the 

 preparation of hsematogen. Mix the portions of ether and distill 

 off the ether. The residue contains the lecithin mixed with fats, 

 cholesterin, and coloring matters. Dissolve this in petroleum- 

 ether and filter. Pour the filtrate into a separatory funnel, add 

 about one-fourth its volume of 75-per-cent. alcohol, and shake. 

 When the two liquids have separated draw off the alcohol, which 

 contains most of the lecithin. Repeat this extraction with alcohol 

 several times and unite the alcoholic solutions. Distill off the 

 remainder of the petroleum-ether from these, and let the solution 

 stand several days in a cool place. A precipitate of cholesterin 

 and other impurities, will form, from which the solution is to be 

 decanted through a filter. Boil the filtrate with a little animal 

 charcoal to decolorize it, and filter. Evaporate at a temperature 

 of 50 to 60 to a syrupy consistency. Cool this and dissolve in 

 ether. If it does not dissolve completely, filter it. Evaporate the 

 ether, when the lecithin remains nearly pure. If desired it can 

 be purified further by dissolving in as small an amount as possible 

 of warm absolute alcohol and placing this in a freezing mixture 

 of 5 to 15 9 , when the lecithin crystallizes out. It should be 

 filtered in the cold. 



68. Place a little lecithin in water and examine with the mi- 

 croscope. Notice the myelin forms. 



69. Warm this mixture with water and notice that after a 

 time the lecithin turns brown and the reaction becomes acid from 

 decompo sition. 



