8 



2ndly. By surrounding fluorescent specimens of fluor-spar with 

 these prepared solutions of the alkaloids, when the blue colour in 

 the spar immediately disappeared. 



3rdly. By photography ; employing concentrated solutions of qui- 

 nine mixed with chloride of ammonium in troughs to intercept the 

 incident light from any object anterior to the camera, when it was 

 found almost impossible to obtain any image upon the sensitive 

 collodion plate, although the intensity of the visible image received 

 on the ground- glass screen did not suffer any apparent diminution. 



4thly. By photographic printing ; troughs containing these solu- 

 tions obstructed the chemical rays very considerably, thus interfering 

 with the production of a positive picture from the negative, much 

 longer exposure being necessary to produce any chemical effect. 



III. That certain reagents do not destroy fluorescence ; others 

 only mask its appearance by their own colour ; whilst some destroy 

 it by neutralizing the excess of acid ; others do so by producing 

 salts which are themselves non-fluorescent media. Whilst a third 

 class destroy it by really modifying the alkaloid itself. 



IV. That as so many reagents of common occurrence interfere with 

 the manifestation of fluorescence, and as it is also a property com- 

 mon to all the cinchona alkaloids herein described, its appearance 

 becomes no longer of any value as a test for quinine. 



V. Brandes's chlorine and ammonia test will discover 1 grain of 

 either quinine or quinidin in 1 gallon of water, but shows no dif- 

 ference between these alkaloids, except in very concentrated solu- 

 tions, when there is a precipitate with quinidin, but not with 

 quinine. 



Quinicine is also influenced by this test, but less extensively. 



VI. Dr. Vogel's first modification of this test is of no apparent 

 value ; but by also employing ammonia, the author has found that it 

 will indicate both quinine and quinidin, detecting readily 1 grain 

 of either in a pint, and showing slight evidence with 1 grain in 10,000 

 grains of water. 



There is scarcely any reaction with quinicine. 



VII. Dr. Vogel's other modifications of Brandes's test are unim- 

 portant, with the exception of the fourth, viz. excess of chlorine, and 

 very little ammonia. This detects 1 grain in about 2000 grs. of 

 fluid very readily, if excess of acid be avoided at first. The test, 



