174 ARRANGEMENT OF THE ELEMENTS IN COMPOUNDS. 



two simple cyanides ; and lastly the properties of compound 

 cyanides are very different from those of the simple cyanides 

 which are supposed to compose them. The simple cyanide of 

 potassium, for instance, is highly poisonous, while the double 

 cyanide of potassium and iron is as mild in its action upon the 

 animal economy as sulphate of soda. But the compound 

 cyanides may be removed from the class of double salts on a 

 speculative view of their constitution, which their anomalous 

 character warrants me in proposing. It is to be premised that 

 the supposed double proto-cyanide of iron and potassium 

 (yellow prussiate of potash) affords no hydrocyanic acid what- 

 ever when distilled with an excess of sulphuric acid at a tem- 

 perature not exceeding 100, which suggests the idea that it 

 does not contain cyanides or cyanogen. Assuming the existence 

 of a new compound radical, N 3 C 6 , which has three times the 

 atomic weight of cyanogen, and may be called prussine, and 

 which is also tribasic or capable of combining with three atoms 

 of hydrogen or metal, like the radical of the tribasic class of 

 phosphates, then the compound cyanides assume a constitution 

 of extreme simplicity. We have one atom of prussine com- 

 bined always with three atoms of hydrogen or metal in the 

 following salts ; in the proto-cyanide of iron and potassium 

 with one of iron and two of potassium ; in the compound called 

 ferro-cyanic acid, with one of iron and two of hydrogen ; in 

 Mosander's salts, with one of iron, one of potassium and one 

 of barium, calcium, &c.; with two of iron and one of potassium 

 in the salt which precipitates on distilling the yellow prussiate 

 of potash with sulphuric acid at 212. To many of these, pa- 

 rallel combinations might be adduced from the tribasic phos- 

 phates. Prussides likewise combine together, producing double 

 prussides, such as : 



Percyanide of iron and potassium 



(red prussiate of potash) . Fe 2 , N 3 C 6 + K 3 , N 3 C 6 

 Prussian blue . . . Fe 2 , N 3 C 6 + Fe 3 , N 3 C 6 



Basic prussian blue . . . Fe 2 . N 3 C 6 -f Fe 3 , N 3 C 6 + Fe 2 O 3 



One of the proximate constituents in the class of salts, is 

 always a metal or hydrogen on the one theory, or the oxide of 

 a metal or of hydrogen on the other. The metal or the oxide 

 in the salt is often spoken of as its radical, or the oxide of its 

 radical, expressions which are perfectly correct, but apt to lead 



