412 [Jan. 22 



compound has not been realized ; nevertheless the importance at- 

 tached by dyers to Mr. Williams' s discovery is well marked by the 

 fact of a gold medal, together with a prize of 10,000 francs, having 

 been proposed for the discovery of a means of rendering stable the 

 beautiful colours dyed by cyanine. 



The crystals submitted to me for examination by M. Menier were 

 distinct prisms, sufficiently well formed for crystallographical deter- 

 minations. They are at present in the hands of Quintino Sella. 

 Their substance possesses a beautiful green metallic lustre with a 

 golden tint, by which, as well as by crystalline form, they are readily 

 distinguished from acetate of rosaniline, which they in other respects 

 much resemble. The crystals are insoluble in anhydrous ether, diffi- 

 cultly soluble in water, but dissolve readily in alcohol. The solution 

 has a magnificent blue colour, with a coppery iridescence on its sur- 

 face. Addition of acids destroys this colour. Ammonia and the fixed 

 caustic alkalies leave the colour apparently untouched ; but it is now 

 produced by a finely divided deep-blue precipitate suspended in the 

 liquid, which may be filtered off, the filtrate separated from it being 

 colourless. 



The green crystals were found to be the iodide of a peculiar basic 

 compound. The iodine is rather firmly held in this compound ; but it 

 may be precipitated from the alcoholic solution by oxide of silver, and 

 exchanged for bromine or chlorine by treatment of this solution with 

 bromide or chloride of silver, when the bromide or chloride corre- 

 sponding to the iodide are produced. The analysis of the crystals 

 gave results indicating unequivocally the formula 



C 30 H 39 N 2 I, 



which received a close confirmation by the examination of a fine 

 platinum-salt crystallizing in rhombic tablets, which is obtained by 

 precipitating the chloride corresponding to the iodide, strongly acidu- 

 lated with hydrochloric acid, by dichloride of platinum. Neverthe- 

 less slight discrepancies between the theoretical values of the formula 

 and the results obtained led me to assume the existence in the crystals 

 of a compound containing less carbon and hydrogen, indeed of a 

 homologous iodide, 



C 28 H 3S N 2 I. 



This hypothesis, not countenanced at first by the remarkable con- 

 stancy which the composition of the iodide presented even after three 



