16 FATS, OILS, AND WAXES 



funnel and shaken once more with a fresh quantity of ether. 

 Two extractions should suffice, but it is safer to extract a 

 third time. The ethereal extracts are then united, washed 

 with a small quantity of water to remove any soap and trans- 

 ferred to a weighed flask ; after evaporating off the ether, the 

 flask is weighed again ; the increase in weight gives the 

 amount of unsaponifiable residue in 5 grams of the sample. 



The isolation and identification of the unsaponifiable 

 residue is of considerable importance for the purpose of 

 establishing whether a given sample of fat or oil is of animal 

 or vegetable origin, since animal fats all contain cholesterol 

 while vegetable fats contain either phytosterol itself or a closely 

 allied substance belonging to the group of phytosterols. 



REACTIONS AND PROPERTIES OF CHOLESTEROL AND 

 PHYTOSTEROL. 



Cholesterol. 



Cholesterol is a monohydric alcohol of the formula 

 C 27 H 45 OH ; its constitution is still unknown, although a great 

 deal of work has been expended on this question. According 

 to Windaus * it would appear to be a secondary alcohol con- 

 taining an unsaturated group as expressed by the formula : 



CrI . CHoCHo Cj[Hj 7 



/ \ 

 CH CH. 



/ \ /\ 



CH 2 CH CHCH 8 



CH 2 CH 2 CH 



\ / II 



CHOH CH 2 



Cholesterol occurs in the bile and forms the chief con- 

 stituent of a certain type of gall stones ; it also occurs in the 

 brain and blood and is the chief alcohol constituent of wool 

 fat. 



It is insoluble in water and crystallizes from chloroform in 

 needles and from ether or alcohol in rhombic plates, m.p. 148- 

 1 50. It may conveniently be obtained by extracting crushed 

 gall stones with ether and evaporating the ethereal extract to 

 dryness. 



* Windaus: " Ber. deut. chem. Gesells.," 1912, 45, 2421; see also Dore"e: 

 " Biochem. Journ.," 1909, 4, 72. 



