3g; MR JOHNSTON ON PARACYANOGEN 



composed by heat in close vessels, a black residue remains, which is generally 

 supposed to be a carburet of iron. This, however, is not necessarily the case. 



A portion of the best Prussian blue of the shops was gradually heated to red- 

 ness in a retort for half an hour, water, hydro-cyanate and carbonate of ammonia, 

 carbonic oxide and nitrogen, were given off. The black matter dissolved in sul- 

 phuric acid, with evolution of hydrogen gas, and the solution diluted with water, 

 gave a precipitate of Prussian blue. Burned with bichromate of potash, it gave 

 the carbon and nitrogen in the proportion of 2 to 1. Heated again to redness for 

 half an hour, the carbon was found to be to the nitrogen as 4 to 1, and this pro- 

 portion was not changed by a third heating for the same length of time. 



It appears, therefore, that while water is present, the decomposition goes on 

 in such a way as to remove all the elements of each atom of cj^anogen as it is decom- 

 posed, without affecting the composition of what remains ; and that, when all the 

 water is drawn off, the affinity of the iron for carbon comes into play, and nitrogen 

 is given off while a carburet of iron is formed. 



Dry prussiate of potash, heated to redness in close vessels, as in the prepa- 

 ration of cyanide of potassium, undergoes a similar decomposition. A portion of 

 the black matter remaining after the separation of the cyanide in this process, 

 gave me the carbon to the nitrogen as 8 to 1. I have not satisfied myself, hoAv- 

 ever, that the black matter thus formed contains paracyanogen at any stage of 

 the process. 



11. — Properties of Paracyanogen. 



1. It is of a black or dark brown colour, and occasionally has considerable 

 lustre. It has no taste or smell, is insoluble in water and alcohol, has a density 

 of about 2, and is a non-conductor of electricity. 



2. Heated to redness in close vessels, it is slowly resolved into cyanogen. 

 In the air or in oxygen, at a red heat, it burns away without residue, forming 

 carbonic acid, and, according to the hygrometric state of the atmosphere, more or 

 less ammonia and hydrocyanic acid. Heated to redness in a close vessel, and 

 suddenly exposed to the air, it burns like tinder. Heated in a moist state in close 

 vessels, ammonia, and carbonic and hydrocyanic acids, are first given off, and af- 

 terwards cyanogen. 



3. Fused with sulphur or phosphorus, or heated to redness in the vapours of 

 these substances, no apparent change takes place. With alkaline sulphurets con- 

 taining an excess of sulphur, an action takes place at a red heat, but without the 

 formation of any sulpho-cyanide. Heated to redness in an atmosphere of dry 

 chlorine or iodine vapour, a very slight action takes place. Chlorine, if moist, 

 disengages vapours which affect the eyes (chloride of cyanogen ?), and among other 

 products muriate of ammonia. 



