6 



The following different methods of detecting the various cinchona 

 alkaloids have been proposed : 



To Bouchardat and Pasteur we are indebted for the use of polarized 

 light as a means of discriminating these alkaloids by the rotatory 

 power which they exercise upon its plane. 



Liebig employs the difference of their solubility in ether for the 

 same purpose. 



Almost all the other tests proposed have for their object only the 

 discovery of quinine. 



Professor Stokes employs fluorescence, combined with the peculiar 

 reaction, in respect to this phenomenon, of hydrochloric acid, alkaline 

 chlorides, &c. Brandes, the green reaction produced by the suc- 

 cessive addition of chlorine and ammonia, whilst Vogel has modified 

 this latter test in several ways. 



Pelletier has employed the agency of a stream of chlorine gas, and 

 Marchand uses nascent oxygen, obtained from puce-coloured oxide 

 of lead and sulphuric acid for the discovery of quinine. 



Leers first proposed a combination of Liebig' s ether test, with that 

 of Brandes' s chlorine and ammonia reaction, as a means of establish- 

 ing the purity of cinchonidin (miscalled by him quinidin, in common 

 with all German chemists). 



De Vry has advised the employment of hydriodic acid or iodide 

 of potassium in order to discover the quinidin of Pasteur. 



Van Heijningen depends on oxalate of ammonia to discriminate 

 quinine from quinidin. 



All these different tests the author has examined most critically, 

 and, as far as it is possible to do so, determined the absolute 

 numerical value of each method experimentally with the following 

 results : 



He first explains MM. Bouchardat and Pasteur's researches on 

 these remarkable alkaloids, from which it appeared that quinine 

 and cinchonidin are powerfully Isevogyrate, quinidin and cinchonine 

 pre-eminently dextrogyrate, and that quinicine and cinchonicine are 

 only slightly dextrogyrate upon plane- polarized light. These eminent 

 experimenters determined also with accuracy the amount of these 

 molecular rotations for each alkaloid. Yet the expensive nature of 

 the apparatus, the complex formula requisite to reduce the observed 

 amount of angular rotation to the normal molecular standard, and 



