II. LIPINS. 



31. Cholesterin. Demonstration of the iodine-sulphuric acid 

 test. Cholesterin crystals are treated with fairly concentrated 

 H 2 SO 4 and one drop of a very dilute iodinie solution. Note the 

 crystalline form and play of colors. Draw. 



32. Lecithin. Preparation from hen's egg yolk. To the 

 alcoholic mixture of egg yolk given out add one-half its volume 

 of ether, shake and set aside in a tightly stoppered hottle till the 

 next laboratory period. Then filter into an evaporating dish and 

 evaporate over a water bath to dryness, taking care the ether does 

 not catch fire. Dissolve the residue in as small an amount of ether 

 as possible and add four or five volumes of acetone, which precipi- 

 tates the lecithin. Collect on a glass rod, allow the acetone to 

 evaporate and use in the following tests. 



Note the physical properties, consistency, color, etc., of lecithin. 

 Is it soluble in water? in alcohol? in chloroform? 



33. Production of "inyclin forms". Place a small piece of 

 lecithin in water under a cover-glass. Examine from time to time. 

 Note especially the surface. Draw. Remove the cover-glass and try 

 drawing out the surface with a glass rod or needle. Note the very 

 fine filaments formed. 



34. Presence of glycerine in lecithin. Try the acrolein test. See 

 under Exp. 30. 



35. Presence of nitrogen. Heat strongly in a dry test-tube 

 a small piece of lecithin. Suspend in the mouth of the tube a strip 

 of moistened neutral litmus paper and a strip of lead acetate 

 paper. Is the paper changed in color? Due to the formation of 

 what substance? What would the lead acetate paper detect if it 

 blackened in color ? 



36. Presence of plwsphorns. Heat a small piece of lecithin 

 with a fusion mixture consisting of 5 parts KOH to i part KNO 3 

 in a crucible, until colorless. Cool, dissolve in a little warm water, 

 acidify with a few drops of cone. HNO 3 and add molybdic solution. 

 A yellow precipitate indicates the presence of P. 



37. Presence of fatty acid. Add a small piece of lecithin to a 

 few cc. of sodium alcoholate in an evaporating dish and evaporate 

 to dryness. Take up with water and add CaCL solution. A white 

 curdy precipitate indicates fatty acid. What is this precipitate? 



Note that lecithin is like a fat in many ways, yet differs in 

 important respects. 



