138 MASS. EXPERIMENT STATION BULLETIN 166. 



Sterols. • 



The stei'ols indicate the percentage of cycUc alcohols in an oil, fat or 

 wax. 



Reagents. — Ninety-five per cent, alcohol : ^ redistilled, free from acids 

 and aldehydes. 



Digitonin solution: 1 gram to 100 cubic centimeters of 90 per cent, 

 alcohol. 



Ethyl ether. 



Windaus Method. ^ — The unsaponifiablc matter is dissolved in boiUng 

 95 per cent, alcohol in the proportion of 1 to 50, and the sterols precipi- 

 tated with an excess of hot digitonin solution. After standing overnight 

 at room temperature, the precipitate is brought into a tared Gooch 

 crucible with 95 per cent, alcohol, washed with alcohol and then with 

 ether, dried in an oven at 100° C, and weighed as digitonin-sterol. 

 Digitonin unites with the sterols, molecule for molecule, to form an 

 addition product without loss. 



From the weight obtained the percentage of sterols can be calculated 

 by the factor 0.2431. 



Limit of error, 0.05 per cent. 



Synopsis of Reaction. — Solution of the unsaponifiablc matter in hot 

 alcohol. 



Precipitation of the sterols with digitonin. 



C27H460H +C55H9l02S =C82Hl4o029 



Filtration and weight of digitonin-sterol. 



'See "Reagents" under "Saponification Number." 

 sZtschr. Phys. Chem., 65, pp. 110-117 (1910). 



