FORMATION OF CYANOGEN. 985 



melted mass, by the action of the matters dissolved upon the 

 insoluble residue ; for this melted mass yields nothing but 

 cyanide of potassium to alcohol, and contains no prussiate. In 

 explanation of the formation of cyanide of potassium in the 

 melted mass, it is stated by Liebig that metallic potassium 

 readily produces that salt when fused with calcined blood, dis- 

 engaging at the same time a considerable quantity of charcoal ; 

 the proportion of nitrogen to carbon, in cyanogen, being one 

 equivalent of the first to two of the last, while in blood, 

 hair, and horn, the proportion is 1 to 6. Now when these 

 animal matters are fused at a high temperature with potash, the 

 free charcoal reduces the potash to the state of potassium ; the 

 latter then acts upon the azotised carbonaceous matter, forming 

 cyanogen, with which it unites. A second mode in which 

 cyanide of potassium is produced, is when ammoniacal gas is 

 conducted over a mixture of carbonate of potash and charcoal 

 at a red heat. This is accounted for by the action of ammonia 

 upon charcoal alone at a red heat ; the gas is entirely converted 

 into hydrocyanic acid and hydrogen (NH 3 and 2C=H,NC 2 

 and 2H). Now hydrocyanic acid decomposes carbonate of 

 potash at a red heat, forming cyanide of potassium. Hence the 

 product of cyanide of potassium is most considerable when the 

 animal matter is used in its natural state, and not previously 

 carbonised, a fact of which the manufacturers of prussiate of 

 potash have long been aware from experience. To account for 

 the subsequent conversion of the cyanide of potassium in the 

 process into prussiate, it is absolutely necessary that iron exist 

 in the fused mass ; but it may indifferently be in the condition 

 of metallic iron, the protosulphuret or the protoxide of iron. 

 The first is readily dissolved by a solution of cyanide of potas- 

 sium with evolution of hydrogen gas (3KCy with HO and Fe 

 =2KCy,FeCy and KO and H) ; the second with the formation 

 of sulphuret of potassium, and the third with that of caustic 

 potash. When the iron is added in the state of protosulphate 

 to a solution of cyanide of potassium, one third of the latter salt 

 becomes cyanide of iron (a brown insoluble matter), which is 

 dissolved by the other two-thirds of the alkaline cyanide, arid 

 the ferrocyanide formed. These processes are not altered in 

 the slightest degree by mixing caustic potash or its carbonate, 

 or the sulphuret of potassium, with the solution of cyanide of 



