1909.] PUBLIC DOCUMENT — Xo. 31. 131 



tered), ivve from carbonate, to 900 cubic centimeters of pure 

 glycerol. 



Hydrochloric acid solution of a strength that approxinuitcOy 

 45 cubic centimeters will neutralize 20 cubic centimeters of the 

 glycerol-soda solution. 



Ether. 



MciJiod. — Into a tared 300 cubic centimeter Erlenmeyer 

 flask are brought 5 grams of fat together with 20 cubic centi- 

 meters of glycerol-soda solution, and heated over a naked flame, 

 rotating continuously, until the saponification is complete, as 

 shoAvn by the mixture becoming perfectly clear. Care should 

 be taken not to overheat and discolor the fat. Fifty cubic centi- 

 meters of hydrochloric acid solution are now added and the 

 flask loosely stoppered^, heated on a water bath, rotating occa- 

 sionally, until the separated fatty acids form a transparent oily 

 layer on the upper surface of the clear liquid. This requires 

 several hours and must not be shirked. The flask and contents 

 are cooled in ice water, and after the fatty acids solidify the 

 solution is decanted through a fat-free filter, using care not to 

 break the insoluble cake; 150 cubic centimeters of hot water 

 are added, thoroughly agitated, and heated as above, cooled, and 

 the solution filtered. This process is continued until the wash- 

 ings are free from acid, about six times. The flask containing 

 the cake of insoluble fatty acids is inverted and allowed to 

 stand in a cool place over night and drain. A convenient filter 

 stand for both filtration and draining is illustrated by Wiley.^ 

 The next day the small particles of fat adhering to the filter 

 are dissolved in the least possible amount of ether and the solu- 

 tion run into the flask. The ether is driven off in a water 

 bath below 70° C, and the insoluble acids dried in an air bath 

 at 100° C. The final drying period should not exceed two 

 hours. 



There are two compensating errors that usually result from 

 this method, which are volatilization of fatty acids and oxidiza- 

 tion of unsaturated acids. The latter is especially serious, and 

 may render of questionable value a determination of the iodine 



• A condenser is ncoessary if liic soliilile arids are to be determined directly. 

 ' Foods and Food Adulterants, United States Dei)artment of Agriculture, Bureau of 

 Chemistry, Bulletin Ko. 13, p. 457. 



