SPONTANEOUS CHANGES IN FATS 19 



Phytosterol crystallizes from alcohol in elongated plates 

 and from ether in slender needles. The melting point of the 

 pure substance varies somewhat according to the source from 

 which it is prepared; it lies somewhere between 135 and 137 

 or it may be as high as 144. The reason for this may be 

 that the various substances obtained from different sources 

 and described as one and the same substance are in reality 

 different substances but all of a phytosterol nature. The 

 colour reactions of phytosterol resemble those of cholesterol. 



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 is recommended by Lewkowitsch. 



The unsaponifiable residue remaining after evaporation of 

 the ether (p. 15) is dried over a water bath and then dissolved 

 in the least possible quantity of absolute alcohol and allowed 

 to crystallize. The crystals which separate should be examined 

 under a microscope ; cholesterol crystallizes in four-sided plates 

 and phytosterol in elongated hexagonal plates. 



The alcohol is then evaporated off completely and the 

 residue is carefully heated with 2 to 3 c.c. of acetic anhydride 

 over a free flame until the liquid boils, the remaining acetic 

 anhydride being evaporated off over a water bath. The resi- 

 due 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 H4'3-H4'8. 



Phytosterol acetate* melts at 125-137. 



SPONTANEOUS CHANGES IN FATS. 



Rancidity. Most fats when exposed to air and light sooner 

 or later become rancid, acquiring an unpleasant taste and smell. 

 The actual cause of this change is as yet but little understood, 



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

 Byronia has the melting point 155-157. 



