DR SAMUEL BROWN ON PARACYANOGEN. 107 



to a white heat, and the shorter the time it is kept at that temperature, the less ni- 

 trogen is lost. The change which it suffers from elevation of temperature resembles 

 that which the same process produces on carbon, boron, and silicon ; after ignition 

 it is very difficult of decomposition, and indisposed to enter into combination. It is 

 soluble in cold concentrated sulphuric acid, and yields a deep-brown, semi-trans- 

 parent solution, from which I have found that it gradually falls, unchanged and 

 anhydrous, on prolonged exposure to the moisture of the atmosphere. This is the 

 only way in which pure paracyanpgen can be prepared, for, taken as it occurs in 

 the retorts, it is saturated with cyanogen, which adheres to it with great obstinacy ; 

 and I have never seen a specimen which did not leave an evident, though inap- 

 preciable, residue after the action of sulphuric acid, as might have been expected 

 from GAY-LUSSAC'S observation that, when paracyanogen remained in his retorts, 

 he always found traces of nitrogen in the cyanogen collected. It likewise dissolves 

 in nitric and hydrochloric acids, but to a much smaller extent. It is insoluble in 

 water, alcohol, ether, oils. When the sulphuric acid solution is poured into water, 

 there falls a bulky hydrate of paracyanogen. This hydrate is produced in several 

 humid reactions, such as that of cyanogen dissolved in alcohol and exposed to the 

 influence of light ; but it is unnecessary to refer to them, as it is with the produc- 

 tion of anhydrous paracyanogen by fire that the present inquiry has to do. These 

 proximate characters are exceedingly well marked, and are quite sufficient for 

 the discrimination of the substance to which they belong. 



In the memoir of A. D. 1838, Mr JOHNSTONE states that paracyanogen is slowly 

 resolved by heat into cyanogen, but without alluding to the experiments which 

 led to this conclusion. As I had not only never succeeded in producing such an 

 effect upon .the pure anhydrous substance, prepared by the process which has 

 been indicated above, but had invariably obtained results directly negative of his 

 proposition, viz. the extrication of unmixed nitrogen, I requested Mr JOHNSTONE 

 to inform me of the manner in which his experiments had been performed. That 

 chemist kindly gave me to understand that he had never effected the total re- 

 solution of the solid into the gaseous isomeric, and that the process by which he 

 had produced the partial resolution, consisted in keeping paracyanogen (procured 

 as the residue of the preparation of cyanogen) at a low red, followed by a higher 

 heat, for sometime, and collecting the gaseous product, which came away less and 

 less rapidly as the operation was continued. Now, I had separated cyanogen in 

 this way from common paracyanogen, but always mixed with more or less nitrogen, 

 less at the beginning and more towards the end of the process, till there was ex- 

 tricated nitrogen alone ; and had inferred that the cyanogen had been retained in 

 the paracyanogen, which yielded it, by its absorptive power. This inference was 

 suggested and corroborated by the considerations that paracyanogen is peculiarly 

 fitted, by its mechanical form, for retaining gases ; that its chemical relation to 

 cyanogen renders it particularly adapted to the absorption of that gas, and that 



