168 DR SAMUEL BROWN ON PARACYANOGEN. 



cyanogen is presented to it in the most favourable condition for retention in a 

 process of which they are simultaneous products ; and the following selection of 

 simple experiments ratifies the suggestion. 



A quantity of paracyanogen was heated, the first product was rejected till 

 the air of the little apparatus, and any gaseous matters which the subject of ex- 

 periment might have absorbed from the atmosphere, were expelled, and then 32, 

 18, and 28.5 volumes were successively collected and examined ; the first was 

 found, after the removal of cyanogen by potassa, to contain 13.3 vol. or 41.5 per 

 cent., the second 14 vol. or 77.7 per cent., and the third 2(5 vol. or 92.8 per cent, 

 of nitrogen ; the volume of nitrogen being greater, and of cyanogen less, as the 

 operation was prolonged. The paracyanogen, which yielded these mixed volumes, 

 was then found to give off nothing but nitrogen. 



Again, a parcel of the same paracyanogen was kept a week in a vessel full of 

 chlorine, by the copious absorption of which it was changed in appearance, having 

 assumed a very light brown colour. One part of this product, treated as in the 

 former case, first gave away chlorocyanic acid alone at a temperature somewhat 

 lower than that of red heat, and then, at a more exalted temperature, unmingled 

 nitrogen. Another portion was boiled several hours in water with a little carbo- 

 nate of potass, filtered, dried at 212, and decomposed by heat; the first 30.1 

 volumes of the product suffered a diminution of only 0.1 vol. by the action of 

 potassa ; and the subsequent volumes suffered none. 



These observations confirm the rationale which I have given of the appear- 

 ance of cyanogen at the beginning of the decomposition of paracyanogen procured 

 in the ordinary way ; especially when they are viewed in connection with GAY- 

 LUSSAC'S discovery of traces of nitrogen in cyanogen produced from bicyanuret of 

 mercury at high temperatures. And the fact that pure paracyanogen (precipitated 

 by the atmospheric moisture from the sulphuric acid solution of the common pro- 

 duct) does not aiford the slightest appearance of cyanogen, warrants the conclu- 

 sion that paracyanogen, once formed from cyanogen (or its elements), cannot be 

 rechanged into cyanogen by heat. Indeed, it would have been anomalous if it 

 had been otherwise ; for it will be found in the sequel, that the higher the tem- 

 perature at which bic} r anuret of mercury is decomposed, the greater is the quantity 

 of paracyanogen produced ; and how should the same cause which converts the 

 cyanogen of the mercurial salt into paracyanogen transform the latter into its 

 gaseous isomeric again ? 



III. Experiments upon the Preparation of Paracyanogen, The following expe- 

 riments were made with bicyanuret of mercury, formed by the reaction of hydro- 

 cyanic acid, prepared by GEIGEE'S process, on the peroxide of mercury, and sub- 

 sequently ascertained to be pure by a humid analysis. 



