162 FATS, OILS AND LIPINES. [cH. VI. 



It melts at i45C. In chloroform solution it is laevorota- 

 tory, [a] = -36-6. 



Its chemical constitution is not yet determined, but 

 it is probably a member of the terpene series. 



179. Preparation of cholesterol from sheep's brain. Sheep's 

 brain is minced, ground with sand, and intimately mixed with three 

 times its weight of plaster of paris. After some hours the hard mass 

 is ground and extracted three times with cold acetone by rubbing 

 well in a mortar. The mixed acetone solutions are filtered and 

 allowed to evaporate spontaneously. The cholesterol crystallises 

 out and is recrystallised from boiling alcohol. 



1 80. Mount a few crystals of cholesterol in water, examine 

 under the microscope, and draw them. Note the rhombic plates, 

 which are often incomplete at one corner. Irrigate the crystals 

 with strong sulphuric acid : they turn red at the edges. Now add a 

 drop of iodine solution : the crystals give a violet colour, changing 

 lo a green, blue, and finally a black. 



181. Salkowski's reaction for cholesterol. Dissolve a little 

 in a few cc. of chloroform ; to the soution add an equal quantity 

 of strong sulphuric acid and shake. The upper layer of chloroform 

 becomes red, the layer of sulphuric acid yellow with a green fluor- 

 escence. 



182. Liebermann-Burchard reaction for cholesterol. Dis- 

 solve a little cholesterol in 2 cc. of chloroform, contained in a 

 perfectly dry tube. Add ten drops of acetic anyhdride, then two 

 drops of strong sulphuric acid, and shake. The solution becomes 

 coloured a deep blue. 



Phospholipins or Phosphatides. As mentioned on p. 153, 

 these are compounds of fatty acids with phosphorus and 

 nitrogen. Maclean* classifies them as follows : 



(A) Monaminophosphatides (N : P = i : i) 



(a) Lecithin. 



(b) Kephalin. 



* Lecithin and Allied Substances, by H. Maclean (Longmans, Green & 

 Co., 1918). 



