Cyanide of Potassium, and on its Applications. 267 



sium, to obtain which it is best to remove with cold water all 

 that is soluble, and to warm the solution with some sulphuret 

 of iron, which easily dissolves in it. The cyanide of potassium 

 is thus obtained, on evaporation, again in the form of ferro- 

 cyanide, and sulphui'et of potassium remains in the mother- 

 ley. 



Preparation of Hydrocyanic Acid. — The cyanide of potas- 

 sium of the preceding process is much better adapted for the 

 preparation of prussic acid than the ferrocyanide; a larger 

 quantity is obtained, and the distillation is easier. It is well 

 known, that on distilling the yellow salt with sulphuric acid a 

 bluish-white powder is deposited, a combination of cyanogen, 

 potassium and iron, the composition of which is analogous to 

 that of cyanide of iron and zinc, and is represented by the 



formula 2 Cfy + |f p^; where Cfy = Cy^ Fe. 



From the formation and composition of this body, it results, 

 that not more prussic acid can be obtained from five atoms of 

 the ferrocyanide, which contain fifteen atoms of cyanogen, 

 than from nine atoms of cyanide of potassium, which only con- 

 tain nine; the other six atoms remain in the bluish-white 

 precipitate. When the yellow salt is converted, according to 

 the above method, into cyanide of potassium, twelve and a half 

 equivalents of hydrocyanic acid are obtained from five atoms 

 of the ferrocyanide, or three and a half equivalents more. 



It is usual to take so much sulphuric acid to decompose 

 one atom of the yellow salt as will suffice to form with the 

 alkali the bisulphate of potash : on employing cyanide of 

 potassium, only one atom of the hydrate of the acid is requi- 

 site. Equal parts of the cyanide of potassium and proto-hy- 

 drate of sulphuric acid are the best proportions for preparing 

 hydrocyanic acid ; that quantity of sulphuric acid exactly suf- 

 fices to form with the whole of tiie potash a neutral sulphate, 

 and with the ammonia originating from the decomposition of 

 thecyanate, thebisulphate of oxide of ammonium. The cyanide 

 of potassium is dissolved in double its weight of water, and the 

 sulphuric acid diluted with three times its weight of water 

 slowly added in small portions : previous to each addition the 

 effervescence must have subsided. 



Preparation of Cyanate of Potash. — The cyanide of potas- 

 sium, prepared according to the method above described, is 

 an excellent means of procuring easily and with very little loss 

 the cyanate of potash. It is most advantageous to make use 

 for this purpose of common litharge which has been previously 

 heated slightly. The cyanide of potassium is fused in a Hes- 

 sian crucible, and the powdered litharge thrown from time to 



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