22 



FATS, OILS, AND WAXES 



(3) U?isaponifiable Residue. 



The following method, originally due to Allen and Thomson, 

 is recommended by Lewkowitsch for the estimation of the 

 unsaponifiable residue. 



Five grams of the fat or oil are saponified by boiling under 

 a reflux condenser with 25 c.c. of alcoholic potash containing 

 1 1-2 per cent of caustic potash for half an hour. The alcohol 

 is then evaporated off and the residual soap is dissolved in 

 50 c.c. of hot water and transferred to a separating funnel of 

 about 200 c.c. capacity, about 20-30 c.c. of water being used 

 to rinse out the dish. After cooling, the mixture is shaken 

 with 50 c.c. of ether and set aside until the ethereal layer has 

 separated. The separation is accelerated by the addition of 

 a little alcohol. The soap solution is then run off from below 

 into a second separating 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 three times with 20 c.c. of water to remove 

 any soap, and transferred to a weighed flask ; after evaporating 

 oft" 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 may be carried out for the purpose of establishing 

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

 vegetable origin, since animal fats contain cholesterol, while 

 vegetable fats contain phytosterol (see p. 48). 



Authors' observations hitherto unpublished. 



