1 6 FATS, OILS; AND WAXES 



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 ; when saponification is 

 complete the alcohol is 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 30-50 c.c. of ether and set aside until 

 the ethereal layer has separated. (N.B. 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 

 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 



*Windaus: " Nachr. K. Ges. Wiss, Gottingen," 1919, 237; see also Dor6e : 

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



