12 FATS, OILS, AND WAXES 



condenser with alcoholic potash in the proportion of about 

 5 gms. of fat to 50 c.c. of alcohol containing from 2-3 gms. of 

 caustic potash. The heating should be continued until on 

 pouring a little of the solution into a large volume of water 

 an opalescent solution free from undecomposed fat results. 

 The time required for this may vary from a few minutes to 

 half an hour or more. 



When the saponification is complete, the contents of the 

 flask should be heated in an evaporating basin over a water 

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

 free fatty acids are required, the residual soap is dissolved in 

 water and suflficient 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. 



In addition to the trihydric alcohol glycerol, all fats contain 

 a sniall quantity of the monohydric alcohols, cholesterol and 

 phytosterol * which constitute what is known as the unsaponi- 

 fiable residue of fats (cf. p. 22). 



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 unsaponi- 

 fiable residue consisting of phytosterol or cholesterol, which 

 may be obtained by evaporating the solvent. 



EXTRACTION OF FATS. 



The isolation of fats from admixture with other substances 

 may be effected by extraction by means of fat solvents. 



* 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 investigation of vegetable fats proceeds. 



t Kossel and Obermiiller : " Zeit. physiol. Chem.," 1890, 14, 599 ; 

 1891, 15. 321. 



