266 Prof. Liebig on the Preparation of 



the operation, clear and colourless as water, and solidifies into 

 a shining white crystalline mass. 



During the fusion brown flocks are seen floating in the 

 fluid mixture, which subsequently unite into a spongy mass 

 and assume a light gray colour. If the crucible be now re- 

 moved from the fire and allowed to cool somewhat, the gray 

 powder generally settles entirely at the bottom ; this is faci- 

 litated by stirring once or twice with the glass rod. The fused 

 mass may now be easily poured into a warm porcelain dish 

 without a particle of the sediment accompanying it. This 

 mass consists of two combinations, of which the cyanide of 

 potassium forms the chief portion ; the other compound is the 

 cyanate of potash, in the proportion of five of the former to 

 one of the latter. The reaction in the fusion of the yellow 

 prussiate with carbonate of potash is as follows : — at the com- 

 mencement, the protocyanide of iron of the ferrocyanide is 

 decomposed, and forms cyanide of potassium with the potash 

 of the alkaline carbonate, and the protocarbonate of iron, 

 which is deprived of all its oxygen at a higher temperature by 

 the cyanide of potassium. In consequence of this reduction, 

 cyanate of potash and pure metallic iron are obtained. 



Let us suppose in the mixture two atoms of ferrocyanide of 

 potassium and two atoms of carbonate of potash, we then 

 have as sum of the constituents, 



Ferrocyanide of potassium. Carbonate of potash. 



Cf Fe^ K-t and K^ O^ + 2 C O^ = Cf Fe^ K^ O^ 

 and 2 C O^. 

 And we obtain after fusion, 



Cyanide of potassium. C)'an3te of potash. Iron. Carbonic acid. 

 Cy* K^ Cy O + K O Fe2 2 C O^. 



From two atoms of the ferrocyanide of potassium we thus 

 obtain five atoms of the cyanide, that is, one-fourth more than 

 by fusing it alone. The cyanate of potash mixed with it has 

 no injurious influence in any one of its applications. The 

 presence of cyanate is readily detected by the effervescence 

 caused from the escape of carbonic acid on the addition of an 

 excess of acid, and an ammoniacal salt is afterwards found in 

 the liquid. The explanation given above of the formation of 

 the cyanide of potassium under the conditions described is not 

 absolutely correct, as the protocarbonate of iron previous to its 

 reduction is decomposed into carbonic acid, carbonic oxide, 

 and the proto-peroxide (black oxide) of iron, at the expense of 

 which an undeterminable quantity of cyanate is formed more 

 than the formula indicates. The metallic iron precipitated 

 and the sides of the crucible are covered by cyanide of potas- 



