the many interfering actions necessary to be guarded against, effec- 

 tually prevented this from ever becoming a process for general 

 adoption, either among chemists or manufacturers. 



Another method of recognizing the presence of quinine is founded 

 on the optical phenomena of fluorescence, which have been investi- 

 gated by Professor Stokes. Whilst endeavouring to turn this pro- 

 cess to account in the quantitative estimation of quinine by means 

 of excessive dilution, and marking the points at which the various 

 phenomena of "epipolism," "fluorescence," and "internal disper- 

 sion" vanish, the author arrived at the following extraordinary re- 

 sults ; premising that he employs the term "internal dispersion" 

 to mean the positive, "fluorescence" the comparative, and "epi- 

 polism " the superlative degrees of the same optical power : 



I. Solutions containing 1 grain in 35,000 of either quinine or 

 quinidin of Pasteur, exhibit epipolism and fluorescence ; solutions 

 with 1 grain in somewhat less than 140,000 grains of water are still 

 fluorescent, with slight internal dispersion. 



When diluted with from 3 to 10 gallons of water, these alkaloids 

 continue to exhibit internal dispersion. 



Solutions of quinicine are only slightly epipolic, and if the 

 change has been perfect, scarcely at all fluorescent, but neverthe- 

 less strongly absorptive of rays of high refrangibility. 



Cinchonidin also exhibits optical phenomena, but in a much slighter 

 degree ; about y-jnj-th part of that of either quinine or quinidin. 



Cinchonine is also fluorescent about y^^th part of the same alka- 

 loids. 



II. That on mixing fluorescent solutions of quinine, quinidin, or 

 other cinchona alkaloid with the soluble chlorides, although all 

 traces of optical phenomena are lost to the eye, yet the media still 

 possess powerfully absorbent powers on the rays of high refrangi- 

 bility, and, if sufficiently concentrated, are wholly opaque to them, 

 without exhibiting any of the phenomena of dispersion, and greatly 

 impede chemical action. 



This was proved by three methods of observation : 

 1st. By introducing vessels containing fluorescent solutions of 

 quinine into other vessels filled with non-fluorescent solutions of the 

 alkaloids, produced by previous admixture with chloride of ammo- 

 nium, when all optical phenomena disappeared from the inner vessel. 



