98 FATS AND ALLIED SUBSTANCES [ch. 



separating funnel to remove alkali. Then evaporate off the ether in an evaporating 

 basin on a water-bath after turning out the flame. Dissolve the unsaponifiable 

 residue in a small quantity of hot 96-98 ^/o alcohol and cool. A crystalline deposit 

 of sterol will separate out. Examine under the microscope and note the elongated 

 six-sided plates. Make 5 c.c. of a chloroform solution of some of the unsaponifiable 

 residue and test for sterols as follows : 



{a) To 2 c,c. of the chloroform extract add 2 c.c. of concentrated sulphuric acid. 

 The chloroform layer develops a reddish-yellow to blood-red colour according to the 

 amount of sterol present. The sulphuric acid layer shows a very characteristic green 

 fluorescence. Pipette off the chloroform into a basin ; it shows a play of colours, blue, 

 green and yellow due to absorption of water. 



(6) To 2 c.c. of the chloroform extract add 20 drops of acetic anhydride and then 

 concentrated sulphuric acid drop by drop. A violet-pink colour appears which later 

 changes to blue and green. 



Lecithins. 



These substances are probably present in all living cells. True 

 (pure) lecithin can be isolated from the animal, but preparations from 

 the plant have hitherto always been mixtures with other substances. 

 Various plant lecithins with such impurities have been isolated from 

 seeds of the Wheat (Triticum vulgare), Castor-oil Plant {Ricinus com- 

 munis), Pea (Pisum sativum), Lupin (Lupinus) and others: also from 

 leaves of the Horse Chestnut (Aesculus Hippocastanum) and root of the 

 Carrot {Daucus Carota). 



Lecithin is a complex substance in which one hydroxyl of the glycerol 

 of a fat forms an ester with phosphoric acid, the latter being also combined 

 with the base, choline (see p. 170). 



CHg • OOC • R 



I 

 CH -OOCR 



i 

 CH2— o 



I 



HO— P = 

 / 



o 



/ 



C2H4 



N = (CH3)3 

 OH 



Lecithins are yellowish wax-like substances which, on exposure to air, 

 rapidly darken and become brown. They are hydrolysed by boiling with 

 alkalies with the production of glycero-phosphoric acid, fatty acids and 



