SAPONIFICATION NUMBER 203 



fat the Koettstorfer number generally lies between 220 and 233, 

 while other fats {e.g. margarine) and oils have lower values, in the 

 neighbourhood of 190 to 200. 



The Koettstorfer number is sometimes known as the " saponifica- 

 tion number," the term " saponification equivalent " being employed 

 to express the mean molecular weight of the fatty acids. 



193. The Determination of the Koettstorfer or 

 Saponification Number. 



In this determination it is advisable that a blank 

 experiment be performed at the same time as the actual 

 experiment, using similar apparatus. 



Two round-bottomed 150 c.c. flasks are fitted with 

 corks, each provided with a glass tube about 3 feet 

 in length, to act as an air condenser. An alcoholic 

 solution of caustic potash is prepared by dissolving 

 about 30 grams of caustic potash in i litre of absolute 

 alcohol. 



Two grams of butter-fat are then weighed out into 

 one of the flasks, and thereafter the two flasks treated 

 in exactly similar ways as follows : — 



Twenty-five c.c. of the alcoholic caustic potash are 



run into each flask from a burette, the air condensers 



fitted, and the solutions boiled gently for a quarter of 



an hour. During the boiling the exact strength of the 



alcoholic-potash solution is determined by titration 



N 

 with — hydrochloric acid, using phenolphthalein as an 



indicator. 



When the boiling has proceeded for the time 

 mentioned, the heating is discontinued, the flasks 

 disconnected from the condensers, and their contents 



N 

 titrated with the — hydrochloric acid, using phenol- 

 phthalein as before. The number of c.c. of acid required 

 by the contents of the blank flask are subtracted from the 



