172 



DR SAMUEL BROWN ON PARACYANOGEN. 



oil (600), had hindered the further extrication of cyanogen during three hours. 

 However, all the remainder of the cyanogen had not been separated from the 

 mercury as paracyanogen ; the solid product was a mixture of that principle, 

 mercury and bicyanuret, only two-thirds of the last having been decomposed. 

 This oil-bath experiment was repeated several times with a view to finishing the 

 reduction by prolonging the operation, but in eight trials the packed tubes 

 burst in about nine hours ; and when removed before that time the cyanuret 

 was never found to have been completely decomposed. In one case, for example, 

 130 grs. gave two-thirds of its nitro-carbon product as paracyanogen, while the 

 cyanogen set free, as indicated by the loss after explosion, was only 0.9 gr. In 

 this form of the process the mercury is so intimately mixed up with the paracy- 

 anogen as not to be visible till it be ground under water ; they may be separated 

 either by levigation, which is a very tedious process, or by rubbing the mixture 

 gently in a leaden mortar, which absorbs the mercury. It is rather difficult to 

 separate paracyanogen entirely from the surface of the lead, on account of its ad- 

 hesiveness ; and for the purposes of analysis it is necessary to weigh the mixture, 

 to weigh the little mortar before and after the trituration, and to subtract the first 

 from the second weight of the mortar for the mercury, and the weight of mercury 

 from that of the mixed product for the paracyanogen. 



9. In order to discover the degree of pressure under which the gaseous pro- 

 duct of these experiments is separated from the mercury in the solid form, I con- 

 structed a sort of differential barometer on the principle of the law of aerial elas- 



Fig. 1. Fig. 2. Fig. 4. 



n 



Fig 3. 



5.0 



9.O 



10 In. 



'e 



jTT 



