410 [Jan. 22, 



nent in air, and forms a closely adhering coat like that which is 

 produced upon the surface of zinc or lead, protecting the metal 

 beneath from further change. 



In many points the chemical reactions of thallium resemble those 

 of silver, to which metal it is also further approximated by the cir- 

 cumstance that the atomic heat of the metal, like that of silver, is 

 double that of the series to which lead belongs. Although there- 

 fore in other physical properties thallium differs greatly from silver, 

 it seems to be more closely allied to that metal than to any other. 



January 22, 1863. 



Major-General SABINE, President, in the Chair. 

 The following communications were read : 



I. " Researches on some of the Artificial Colouring Matters. 

 No. I. On the Composition of the Blue Derivatives of the 

 Tertiary Monamines derived from Cinchonine." By A. W. 

 HOFMANN, LL.D., F.R.S. Received December ]8, 1862. 



The chemical visitors of the International Exhibition will not easily 

 forget the magnificent collection of products displayed in the French 

 court by M. Menier of Paris. Among these compounds, equally 

 remarkable for their variety and beauty, the large crystals of cyanine, 

 rivalling in splendour and purity Mr. Nicholson's acetate of 

 rosaniline, have attracted general attention. M. Menier, who has 

 produced this new dye on a very large scale, has most liberally placed 

 at my disposal some of the finest of these crystals for examination, 

 hoping that their more minute investigation might perhaps lead to a 

 method of giving solidity to this new colour, which in brilliancy and 

 purity of tint is second to none of the several blues lately derived 

 from coal-tar. The composition of cyanine and its mode of forma- 

 tion having hitherto remained unknown, I have gladly availed myself 

 of this opportunity of performing some experiments with this inter- 

 esting compound. I am sorry to say that, in a practical point of 

 view, these experiments have failed entirely ; but my studies have 

 led me to some observations on this substance which, as a contribu- 

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

 beg leave to communicate to the Royal Society. 



