50 FATS, OILS, AND WAXES 



under a microscope ; cholesterol crystallizes in four-sided plates 

 and phytosterol in elongated hexagonal plates. 



Cholesterol and phytosterol cannot with certainty be dis- 

 tinguished by means of their melting-points, owing to the fact 

 that phytosterol may melt at any temperature between 135 

 and 144° according to the source from which it is prepared. 

 As, however, there is a considerable difference between the 

 melting-points of the acetates of these two substances the 

 following procedure may be adopted. After completely 

 evaporating off the alcohol, the residue is carefully heated 

 with 2-3 c.c. of acetic anyhdride over a free flame until the 

 liquid boils, the remaining acetic anhydride being evaporated 

 off over a water bath. The residue is then re-crystallized two 

 or three times from the least possible quantity of absolute 

 alcohol, and the melting-point of the crystals so obtained is 

 determined. 



Cholesterol acetate melts at ll4*3-ii4-8°. 



Phytosterol acetate * melts at 125-137°. 



Stigmasterol acetate melts at 141°. 



Since cholesterol and phytosterol are the sterols charac- 

 teristic of animal and vegetable fats respectively the above 

 procedure may be adopted for distinguishing the source of 

 origin of a given fat, or for detecting the presence of vegetable 

 fat in animal fat. For this purpose a melting-point of the 

 sterol acetate up to 116° is taken to imply the absence of vege- 

 table oil, but a melting-point of 117° or more indicates con- 

 tamination with vegetable oil. 



ESTIMATION OF THE STEROL CONTENT OF AN 

 UNSAPONIFIABLE RESIDUE. 



The method devised by Windaus f depends upon the 

 formation of an insoluble compound of the sterols with 

 digitonin. 



The unsaponifiable residue obtained by the method already 

 described, is dissolved in twenty times its weight of alcohol ; it 

 is then warmed to 65° and treated with a I per cent solution 



* The acetyl derivative obtained by Power and Moore from the root 

 of Bryonia has the melting-point 155-157°. 



t Windaus : " Zeit. physiol. Chem.." 1910. 65, no. 



