216 ODOROGRAPHIA. 



has become coloured in this way is quickly decolorized if shaken 

 with calcium carbonate ; granulated zinc likewise causes it to turn 

 brownish. Spectroscopic examination of the coloured oil furnishes 

 no phenomena of peculiar interest. Chromic acid dissolved in 

 chloroform does not perform the same reaction as nitric acid.' 

 The professor discovered, a few months later,* that Japanese and 

 Chinese oil of peppermint does not partake of this reaction at all ; 

 it is not coloured by nitric acid (sp. gr. 1"20) even when gently 

 warmed with it. 



It has been remarked by Dr. Polenske, technical assistant to the 

 German Imperial Health Department, that peppermint oil which 

 had stood for some time in sunlight lost the power of giving colour 

 reactions with acids. This observation is of particular practical 

 importance. 



The Dutch Pharmacopoeia requires as a test for the identity of 

 peppermint oil that a mixture of 5 drops with 20 drops of glacial 

 acetic acid shall gradually develope a dark blue colour, with a 

 copper-coloured fluorescence. 



It has been remarked by Messrs. Schimmel & Co. that the 

 formation of the colouring compound was dependent on a process 

 of oxidation, and did not occur when air was excluded. If a small 

 bottle is completely filled with the mixture of peppermint oil and 

 glacial acetic acid and closed with a cork, the liquid becomes a 

 scarcely perceptible blue, which, however, does not deepen in 

 intensity even when the mixture is allowed to stand for days. If> 

 however, the bottle is opened and the air thus enters, the mixture 

 gradually darkens in colour, and by reflected light shews a 

 beautiful copper-coloured fluorescence. It should be mentioned 

 that a certain time is necessary for the reaction to clearly develop, 

 and that hours often elapse before the fluorescence has attained its 

 maximum. Japanese peppermint, of which various samples were 

 examined, either gives no colour reaction at all, or only to a very 

 slight extent. 



Commercial oil of peppermint is usually adulterated to the extent 

 of 30 per cent, at least. The yellow resinous oil sold under the 

 name of " American " or " Crude oil of peppermint " consists 

 chiefly of oil of turpentine, and on evaporation leaves a residuum 



* Pharm. Journ. [3], ii., p. 321. 

 t Bericht, October, 1890. 



