80 Mr Johnston on a solid form of Cyanogen, 



and carefully dried at a heat not above 212°, gives a deep 

 chocolate powder, having the smell and taste of rhubarb. 

 Caustic potash decomposes it, giving off ammonia. Heated 

 in a tube it gives white fumes, which condense on the sides of 

 the tube and resemble rhubarb in colour, smell, and taste. 

 When fumes cease to be given off, there remains a bluish-black 

 substance of considerable density and lustre, and breaking 

 like thin layers of coal into rectangular fragments. 



Of this substance 8 grains were exploded with 8 grains of 

 chlorate of potash. The products were 



Carbonic acid, - - 2.75 inches 

 Azote, - - - 1.4 



Now the weight of the carbon in the carbonic acid, added to 

 that of the azote = .77 grains, which is near enough to .8 

 grains, the quantity employed, to be completely within the li- 

 mits of error. 



In this experiment, as in all the others above detailed, the 

 carbon is to the azote as 2 : 1 ; we are warranted therefore in 

 concluding, that the deposit from alcohol supersaturated with 

 cyanogen, when dried by a sufficient heat, is a solid hi-carhu- 

 ret of azote. In the sequel of this paper we shall have further 

 reason for concluding it to be identical also with the carbo- 

 naceous matter remaining from the decomposition of the cyanide 

 of mercury. 



One question occurs here to which we may advert. If this 

 substance be identical in composition with gaseous cyanogen, 

 does the difference in their properties arise from a new arrange- 

 ment of the elements, or merely from their closer aggregation.'' 

 It is nothing new in chemistry for substances of very different 

 properties to be identical in composition. Of this kind are the 

 acetic and succinic acids, but the number of atoms (=9) they 

 contain, leaves ample room for various changes of arrangement. 

 In the present case, however, there are only three atoms united, 

 and of these two are carbon, so that there cannot by possibility 

 be more than two identical combinations of these elements. 

 There may be more if the atom of this solid bicarburet be 

 greater than that of cyanogen, but this we are not entitled to 

 assume till its compounds be investigated. Still, even if the 

 atomic weights of these two compounds be the same, one dif- 



