PHYTOSTEROL 17 



alcohol containing an unsaturated group as expressed by 

 the formula : 



CH 



CH . CH 2 . CHCH 3 . [CH,J S . CH(CH 3 ) 2 



HC CH 



2 2 



H 2 C CH CH 



HO.C.H CH 



Cholesterol occurs in the bile, certain gall stones, brain, 

 blood and wool fat. It is insoluble in water and crystallizes 

 from chloroform in needles and from ether or alcohol in 

 rhombic plates, m.p. 148-150. It may conveniently be ob- 

 tained by evaporating the ethereal extract of gall stones to 

 dryness. 



Reactions. (i) Crystals of cholesterol pressed on a white 

 porcelain surface and moistened with a drop of sulphuric acid 

 (5 parts concentrated acid to I part of water) turn pink. The 

 addition of a drop of dilute iodine causes a play of colours 

 from red to blue or green. 



(2) A solution of cholesterol in chloroform gently agitated 

 with concentrated sulphuric acid turns red, while the sulphuric 

 acid which forms the lower layer assumes a green fluorescence. 



(3) On the addition of concentrated sulphuric acid drop 

 by drop to a little cholesterol dissolved in a mixture of 2-3 

 drops of chloroform and about 10 drops of acetic anhydride, a 

 transient pink colour is at first formed ; on the addition of 

 more acid, however, the colour changes to blue and finally to 

 green. 



(4) Alcoholic solutions of cholesterol mixed with a few 

 drops of I per cent alcoholic solution of digitonin,* give an 

 immediate white precipitate, C 27 H 46 OC 54 H 92 O 28 , a reaction em- 

 ployed in the estimation of cholesterol.f 



* Panzer: " Chem. Zentr.," 1912 (ii.), 540. 



fWindaus: " Ber. deut. chem. Gesells.," 1909, 42, 238; " Z. physiol. 

 Chem.," 1910, 65, no; Salomon: "Ber. deut. pharm. Gesells.," 1914,24, 189. 



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