ANALYSIS OP BUTTER-FAT. 67 



beKeves " leaves nothing to be desired on the score either of 

 facility of execution or of accuracy," is shortly described, as 

 follows : — ^A weighed quantity of butter-fat is saponified in a 

 strong closed flask by means of a measured volume of 

 standard alcoholic potash, 25 c.c. of a solution of the 

 ordinary standard strength being used to decompose 5 grammes 

 of the fat. The caoutchouc stopper with which the flask is 

 closed must be firmly tied with string. After heating in 

 the water-bath for about an hour the contents of the small 

 flask are carefully washed into an ordinary flask, the alcohol 

 is dissipated by heating, and 25 c.c. of a standard sul- 

 phuric acid, of somewhat greater strength than the alcoholic 

 potash, are added. The fatty acids which are thus liberated 

 are allowed to solidify, and the acid liquid containing the 

 soluble fatty acids and the excess of free mineral acid is 

 passed through a filter. The insoluble fatty acids are 

 washed in the flask, and weighed in the flask after due 

 drying, the small quantity on the filter being extracted by 

 means of ether, at a temperature of 105° C. Thus the 

 quantity and the percentage of insoluble acids are arrived at. 

 By simply determining the acidity of the filtrate and sub-, 

 tracting from the total acidity the quantity corresponding to 

 the excess of acid employed, the proportion of soluble fetty 

 acids is arrived at, which are calculated as butyric acid. 



Thus Dr. Dupre found that " butter-fat really does contain 

 from 5 to 6 per cent, of soluble fatty acids." 



He also found that, if the saponification took place in an 

 open flask a considerable loss of butyric acid took place, 

 some butyric ether being volatilised, as may readily be 

 perceived by the smeU. This loss amounted to as much ae 

 0'76 per cent. We were led to a similar result by direct 

 determination, by Berthelot's method, of the butyric ether 

 distilled off during saponification. 



In no case do Dr. Dupre's results add up to 100. 



