UNSAPONIFIABLE RESIDUE 15 



bath, and thoroughly stirred to get rid of the alcohol. If 

 the free fatty acids are required sufficient sulphuric acid is 

 then added to make the solution strongly acid, whereupon 

 the fatty acids separate out and rise to the surface. 



The aqueous layer contains the glycerol together with the 

 excess of sulphuric acid and potassium sulphate. 



CHOLESTEROL AND PHYTOSTEROL. 



In addition to the trihydric alcohol glycerol, all fats contain 

 a small quantity of the monohydric alcohols cholesterol and 

 phytosterol * which form what is known as the unsaponifiable 

 residue of fats. 



These substances may be isolated from fats according to 

 the following method devised by Kossel and Obermuller.f 



An ethereal solution of the fat is mixed with a solution 

 of sodium in alcohol ; saponification takes place in the cold 

 and the soap which is precipitated from solution can be filtered 

 off; the filtrate, which is a mixture of alcohol and ether, 

 contains the glycerol together with the so-called unsaponifiable 

 residue consisting of phytosterol or cholesterol which may be 

 obtained by evaporating the solvent. 



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 ai " 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 



* The term phytosterol though employed by many authors to indicate a single 

 definite substance is beginning to be used as a generic term for a whole group of 

 closely allied substances the number of which is rapidly increasing as the investi- 

 gation of vegetable fats proceeds. 



f Kossel and Obermiiller : " Zeit. physiol. Chem.," 1890, 14, 599 ; 1891, 15, 321. 



