1894.] p. C. Roy—In,li(tu Fuo'lshiffs. Fal aud Oil. 45 



such Indian Foodstuffs as mustard oil, butter, fjhei\ &c., which might be 

 ef some help in deciding cases of falsification. 



Particular care was taken in procuring genuine samples of substances. 

 The oils were in many cases expressed under direct supervision from 

 seeds carefully selected, so that the purity of the products was unques- 

 tionable. A sample of pure mustard oil was also obtained through the 

 courtesy of the Superintendent, Alipur Jail, and another of cocoauut oil 

 from the officer in charge of the Kopi'a works. Viper Island, Port Blair-> 

 with a certificate from him guaranteeing its purity and stating it to be 

 a standard sample. 



The preliminary examination of fats and oils is much helped by 

 the application of certain physical tests, e. g., melting point, specific 

 gravity, index of refraction, &c. The work is at present confined solely 

 to the chemical methods. The determination of the physical constants 

 has been reserved 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 ghjcerides. Qy estimating the amount 

 of either or both of these constituents of fatty substances, valuable in- 

 formation is often obtained as to their nature. Now, if a fat be treated 

 with an alkali, the fatty acids contained in the former, combines with 

 the latter, resulting in the formation of an alkaline salt, 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, occurring in butter-fat, has a molecular 

 weight equivalent to 88, while erucic acid, a component of mustard oil, 

 Las a molecular weight of 338. A molecule of caustic potash weighing 

 56, will exactly neutralise 88 parts by weight of butyinc acid, or 338 

 parts by weight of erucic acid. Hence a given weight of butter-fat will 

 require a far larger proportion of caustic potash to convert it into soap, 

 to saponify it, as it is called, than the same weight of mustard oil. Koett- 

 storfer 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 

 20 grammes of caustic potash for saponification, the same weight of 

 mustard oil requires only 17 grammes of the alkali. The amount of 

 glycerin also will vary in the same manner. Again, butyric, caproic, 

 and other volatile acids, present in cocoauut oil, butter-fat, &c., may be 

 easily separated from the non-volatile acids by distillation, and their 

 amount ascertained by their potash neutralising power. Upon this prin- 

 ciple is based the well-known Reicherts' test. The amount of iodine 

 absorbed by different fats and oils also lies within wide limits. The 

 iodine absorption has been employed with remarkable success by Baron 

 Hiibl in deciding cases of adulteration. 



