Hofmann on the Blue Derivatives of the Tertiary Monamines. 231 



tion to the history of cyanine, deserve to he recorded, and which I 

 beg leave to communicate to the Royal Society. 



The discovery of the blue compounds from chinoline and its homo- 

 logues dates as far back as 1856. In that year Mr. G. Williams 

 engaged in a renewed examination of the base extracted by Runge 

 from coal-tar and obtained by Gerhardt from the alkaloids of the 

 cinchona bark, the identity in composition of which I had established 

 in one of my earlier researches. Among the numerous compounds 

 of these bases most carefully examined by Mr. G. Williams on this 

 occasion, were also their methylated and ethylated derivatives, one of 

 which, the iodide of methyl-leucolylammonium, I had discovered 

 when studying the action of iodide of methyl upon ammonia and its 

 analogues. It was in preparing this compound from the chinoline 

 obtained by the distillation of cinchonine, and in separating the am- 

 monium-base corresponding to the iodide by means of oxide of silver, 

 that Mr. Williams first observed the splendid coloration which has led 

 him to the discovery of the new dye now commercially known under 

 the name of cyanine. Precisely similar phenomena were subse- 

 quently (in 1857) observed by M. von Babo, who produced them by 

 treating chinoline with the sulphates of methyl and ethyl, and 

 described the poloured substances thus obtained as methylirisine and 

 ethylirisine. Mr. Williams was inclined to attribute the formation 

 of the blue compounds, in which he recognized distinctly basic pro- 

 perties, to a process of oxidation ; M. von Babo represents his methyl- 

 and ethylirisine, although with very great reserve, by the formulae 



C u H 14 N a O a and C 13 H 18 N 2 2 . 



No attempt has since been made to establish the composition of 

 these singular compounds by a more minute examination. In fact 

 several years elapsed without any further notice being taken of them, 

 until the development of the aniline industry revived the memory of 

 these remarkable colour phenomena, which have since attracted the 

 general attention of dyers and printers. Mr. G. Williams showed 

 that, among the several coloured compounds produced by the action 

 of iodides of alcohol radicals upon chinoline bases, the one obtained 

 by means of iodide of amyl is particularly rich in tinctorial power ; 

 he has given a very interesting account of this new dye, and accu- 

 rately described the mode of manufacture of this body, which, under 

 the name of cyanine, soon became an article of commerce. 



Unfortunately the tint produced by cyanine is less fast than beau- 

 tiful, and the hopes entertained of the industrial future of the new 

 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 



