60 P. C. Ray— CA.cmicaZ Examination of [No. 1, 



necessary to work out in the first instance a series of constants for such 

 Indian food-stuffs as mustard oil, butter, ghee, &c., which might be of 

 some help in deciding cases of falsification. 



Particular care was taken in procuring genuine samples of the 

 substances. The oils were, in many cases, expressed under direct super- 

 vision from seeds carefully selected, so that the purity of the products 

 was unquestionable. A sample of pure mustard oil was also obtained 

 through the courtesy of the Superintendent, Alipur Jail, and another of 

 cocoanut oil from the officer in charge of the " Copra " works, Viper 

 Island, Port Blair, with a certificate from him, guaranteeing iis purity, 

 and stating it to be a standard sample. 



The preliminary examination of the fats and oils is much helped 

 by the determination of certain physical constants, e. g., melting point, 

 specific gi'avity, index of refraction, &c. The work in the present com- 

 munication is confined solely to the chemical methods. The application 

 of the physical tests, is i*eserved for a future occasion. 



The fats and oils are simply combinations of certain acids, the 

 so-called fatty acids, e. g., butyric, stearic, oleic, palmitic, &c., with 

 glycerin ; hence they have been named the glycerides. By estimating 

 the amount of both or either of these coustitaeuts of fatty substances, 

 valuable infoi'mation is obtained as to their nature. Now, if a fat 

 be treated with an alkali, the fatty acids contained in it com- 

 bine with the alkali, resulting in the formation of organic salts, 

 commonly called a soap, and the separation of glycerin. It so 

 happens, however, that the molecular weights of some of these fatty 

 acids vary within wide limits. Thus, butyric acid, occuri'ing in butter- 

 fat has a molecular weight equivalent to 88, while erucic acid, a compo- 

 nent of mustard oil, has a molecular weight of 338. A molecule of 

 caustic potash weighing 56, will exactly neutralise 88 parts by weight 

 of butyric acid or 338 parts by weight of erucic acid. Hence a given 

 weif^ht of butter-fat will require a far larger proportion of caustic 

 potash to convert it into soap — to saponify it, as it is technically called — 

 than the same weight of mustard oil. Koettstorfer has made use of 

 this principle. It has in fact been found by actual experiments that 

 while 100 grammes of butter-fat require very nearly 22 grammes of 

 caustic potash for saponification, the same weight of mustard oil requires 

 only 17 grammes of the alkali. The amount of glycerin in a fat or oil 

 also will vary in a corresponding manner. 



Again butyric, caproic and other volatile acids present in cocoa-nut 

 oil, butter- fat, &c., may be easily separated from the non- volatile acids 

 by distillation, and their amount ascertained by their potash neuti-alis- 

 i"g power. Upon this principle is based the well-known Reichert s 



