70 



FOODS AND FOOD ADULTERANTS. 



that an alcoholic solution of a fat acid is immediately saponified by the 

 addition of alcoholic potash, while a neutral fat requires time and heat 

 to secure complete saponiti cation. 



When, therefore, an alcoholic solution of fat acids and neutral fats to 

 which phenol-phthaleiu has been added is titrated with caustic potash* 

 the red color only appears when the fat acids are saponified, and only 

 comes permanently when all the fats are saponified. When the red 

 color appears an excess of caustic potash is added and the whole boiled for 

 half an hour to saponify all the neutral fats and retitrated, whereby the 

 amount of caustic potash required to effect the saponification of all the 

 fats is ascertained, and the quantity of potash required for each titra- 

 tion represents the relative proportion of fat acids and neutral fats in 

 the mixture operated on. When a neutral fat is saponified the follow- 

 ing reaction takes place : 



C 3 H 5 



KOH=C S H 6 (OH) 3 +3 K 



and therefore every litre of normal potash splits up one-third equivalent 

 of glycerine, i. e., 30.667 grams. One cubic centimeter normal potash is 

 therefore equivalent to 0.030667 gram glycerine. The theoretical yield 

 of fat acids could also be calculated by the following formula: 



C 3 H 5 (C n H 2n _ 1 O 2 ) 3 = C3H 5 C n H 2n _ 1 O 2 . 



Then one litre normal potash represents one-third equivalent of gly- 

 cerine residue, or 12.667 grains. If 5cc. normal potash have been em- 

 ployed the weight of the glycerine residue would be .012667x5. 



F. W. A. Woll 1 gives the results of his studies with butter and artifi- 

 cial butter. 



Mixtures of pure butter with "oleo oil" were made and examined by 

 the methods of Koettstorfer and Keichert, and the results compared 

 with theory. The following numbers were obtained : 



NOTE. It is very easy to get exact results by the above method of mixture. But- 

 ter and an oil are used whose behavior with the reagents employed was determined 

 by preliminary experiment. The case is very different when the analyst is called on 

 to examine an unknown sample. The butter in an unknown sample may have quite 

 a different per cent, of volatile acid from that used in the samples given. The value 

 of this method, therefore, is seriously impaired for determining the extent of adul- 

 terations in case where the separate examination^of the constituents is impossible. 



!Zeit. Anal. Chem., 1884, p. 28, and Am. Chem. Jour., vol. 9, p. 62. 



