106 



FIXED OIL, ETC. 



detected, according to Jacobson, 1 by shaking with powdered 

 rosaniline. Oil containing free fat-acid is coloured red. 



Rumpler 2 employs carbonate of soda, which does not emulsify 

 oils containing no free fat-acid. 



Geissler 3 estimates the free fat-acid by diluting with 2 or 3 

 volumes of ether and titrating with alcoholic potash, using an 

 alcoholic solution of rosolic acid or phenol-phthalein as an indi- 

 cator. 



126. Cholesterin. Detection and Estimation. Hoppe-Seyler* 

 -detects and estimates cholesterin in vegetable substances by ex- 

 tracting with ether, distilling, boiling the residue for a few hours 

 with alcoholic potash, evaporating, redissolving in water, and 

 shaking with ether. If the cholesterin obtained by evaporating 

 the ethereal solution is not pure, the treatment with alcoholic 

 potash is repeated. If sufficient alkali is present neither fat nor 

 soap will be taken up by the ether. 



Schulze 5 directs attention to the fact that the estimation is 

 inaccurate if the material contains vegetable wax yielding an 

 alcohol ( 14) on decomposition with an alkali, on account of the 

 influence the latter exercises on the solubility of cholesterin in 

 spirit. Schulze recommends the conversion of the impure cho- 

 lesterin into benzoate of cholesteryl by heating with benzoic acid 

 in sealed tubes. This compound may be freed from many foreign 

 substances by boiling with absolute alcohol, in which it is almost 

 insoluble. After recrystallization from ether the cholesterin may 

 be liberated by heating with alcoholic potash. 



Cholesterin is soluble in petroleum spirit as well as in ether, and 

 is therefore extracted by the former, together with the fixed oil. 

 If an accurate estimation is required, large quantities of material 

 must be worked upon, as cholesterin occurs in only small prc 

 portions in vegetable substances. (Beneke obtained 1'5 grai 

 from 2,500 grams of grey peas.) It is insoluble in water, crystal- 

 lizes from alcohol in silky needles and plates (belonging to th( 

 rhombic system), melts at 137, and is, in alcoholic solutioi 

 laevo-rotatory (a D = 36'61). Warmed with a mixture of 1 voi 



1 Chem.- tech. Eepert. i. 84 ; Zeitschr. f. anal. Chemie, xvii. 387, 1878. 



2 Zeitschr. f. anal. Chemie, ix. 417, 1870. 



3 Ibid. xvii. 387, 1878 (Journ. Chem. Soc. xxxiv. 334). 



4 Med.-chem. Unters. Heft i. 143. Zeitschr. f. anal. Chemie, v. 422, 1866. 



5 Zeitschr. f. anal. Chemie, xvii. 173, 1878. (Journ. Chem. Soc. xxxiv. 612. ; 



