Mr Johnston on a solid form of Cyanogen. 77 



each of the following experiments, the carbonic acid is so near-i 

 ly double of the azote, that there can be no doubt of this sub- 

 stance being composed, like gaseous cyanogen, of 



2 atoms carbon, 



1 azote, 



No. 1 3.04 inches. 2.0 inches. 1.04 inches. 



Mean, 3.493 2.32 1.173 



When prepared according to this process, I have found it 

 impossible to obtain this compound entirely free from metallic 

 mercury ; minute globules remaining attached to it after the 

 most careful separation. Hence, in analyzing it, the weight of 

 the resulting carbon and azote, in the above experiments, never 

 equalled the weight of the carbonaceous matter employed. By 

 exposing it to heat in a glass capsule over the flame of a spirit 

 lamp, the mercury is volatilized and completely driven off; 

 but before this is effected, a change in the composition of the 

 substance itself takes place, of which I shall have occasion here- 

 after to take notice. 



It became desirable, therefore, to find another process for 

 obtaining this compoimd by which the presence of metallic or 

 other foreign bodies might be completely prevented. It is 

 known that when cyanogen is allowed to stand over mercury 

 for a sufficient time, a black substance is deposited on the 

 sides of the containing vessel. It is known also that when a 

 solution of caustic potash saturated with cyanogen is exposed 

 to an excess of that gas, the liquid becomes brown from the 

 intermixture of black particles which seem about to be depo- 

 sited. In both cases, it has been supposed, or rather taken 

 for granted, that a portion of the cyanogen is decomposed, 



