which exhibit the phenomena of Fluorescence. 87 



portion of two equivalents of the latter to one of the former, 

 a brownish-red solution results, which exhibits a blue appear- 

 ance at the edges. If to such a solution successive portions of 

 either the platinum salt, or the iodide of the alkali, be added, 

 the fluorescence gradually diminishes, and eventually ceases 

 to be discernible. What the fluorescent compound here is I 

 have not been able to ascertain with any degree of certainty. 

 Pure biniodide of platinum is insoluble in water, and its solu- 

 tion in iodide of potassium is of a most intense red, without 

 any superficial blue. Probably chlorine in some condition 

 forms a constituent of the compound ; indeed the fluorescence 

 was found to be rather increased than otherwise by the addi- 

 tion of chloride of potassium, though the red colour was con- 

 siderably reduced. That this internal dispersion was not due 

 to mere opalescence, was proved by its not being exhibited 

 when the incident light had passed through quinine salt. 



Besides these experiments on iron and platinum salts, I have 

 made several with the specimen of comenamic acid which you 

 were kind enough to give me. I subjoin the results. 



Alkaline Comenamates. — I found that an aqueous solution 

 of the acid itself is absolutely devoid of dispersive power upon 

 a ray of light, but that when combined with an alkaline base 

 it is very fluorescent. If excess of potash be added, a blue 

 results which is almost equal to that of bisulphate of quinine ; 

 and as the solution is itself perfectly transparent and colour- 

 less, it may serve as a good additional means of analyzing 

 light. The blue does not appear when the comenamate of 

 potash is placed in a ray that has traversed a solution of qui- 

 nine salt, or of prussian blue in oxalic acid ; but it is rendered 

 very visible in a ray which has passed through the ammonia- 

 cal copper salt. On throwing a prismatic spectrum upon a 

 solution of this salt, the blue dispersion was found to take 

 place in the violet portion of the beam. 



The comenamate of soda resembles the potash salt. 



The ammonia salt, the epipolic dispersion of which Mr 

 How has mentioned in his paper (Trans. Roy. Soc. Ed. xx,, 

 Pt. 2), was also examined. I found it required great dilution 

 to bring out the effect properly ; and it did not seem to me to 



