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X. On the Preparation of Paracyanogen in large quantities, and on the Isomerism 

 of Cyanogen and Paracyanogen. By SAMUEL M. BROWN, M.D. Communicated 

 by ROBERT CHRISTISON, M.D., F.R.S.E., &c. 



(Read 15th February 1841.) 



THE design of the processes described in this memoir was to decompose the 

 bicyanuret of mercury at such a temperature, and under such a degree of pressure, 

 as to secure the simultaneous extrication of the two equivalents of cyanogen, or 

 their elements, in the expectation that they should come off united, and produce 

 the interesting compound of nitrogen and carbon, isomeric with cyanogen, Para- 

 cyanogen : And that result was sought in the belief that it would illustrate the 

 chemical theorem of the existence of bodies which, though composed of the same 

 elements in the same proportions, yet differ as widely from each other in chemical 

 properties and mechanical conditions, as one element differs from another. 



I. History of Paracyanogen. M. GAY-LUSSAC* observed, in the course of his 

 admirable researches on the prussic acid, that it is spontaneously decomposed on 

 exposure to light, ammonia being liberated and a brown solid matter deposited. 

 From experiments made in vacuo it appeared that these were the sole products of 

 the reaction of the elements of the acid on each other, so that the deposit neces- 

 sarily contained nitrogen, and, without analysis, it was inferred to be " un azoture 

 de carbone." 



When M. GAY-LUSSAC proceeded to the discovery of cyanogen and the com- 

 position of the cyanurets, he procured cyanogen from the prussiate of mercury, 

 which he represented as a true bicyanuret. Among other processes, he had 

 recourse to the decomposition of the mercurial cyanuret by the oxide of copper, 

 in order to determine the quantitative composition of cyanogen. The results of 

 this analysis coincided with those of his other methods, and confirmed his view 

 of the nature of the so-called prussiate ; but there was one circumstance which, 

 at first sight, seemed to throw suspicion on these conclusions. " Cependant, s'il 

 en est ainsi, pourquoi reste-t-il une matiere charbonneuse lorsqu' on decompose le 

 cyanure par la chaleur? Cette difflculte m'embarrasse' pendant quelque terns; 

 mais je crois etre parvenu a la re'soudre." He then states that he found, that, when 

 the carbonaceous matter, now known by the name of paracyanogen, is left in the 

 retort after the reduction of the cyanuret by heat, nitrogen appears in the gaseous 

 product in such a proportion as very nearly to make up the equivalent weight of 



* Ann. de Ch. 1815. 

 VOL. XV. PART I. Y y 



