176 ON THE MANUFACTURE OF PRUSSIATE OF POTASH. 
from the calcination of bones, &c., and finally, the atmos- 
pheric air. 
The theory of reaction, in all the processes, is identical, 
and results from the fact that when nitrogen alone, or in 
combination, is brought into contact with a mixture of pot- 
ash and carbon, at a bright red heal, cyanogen is produced 
by the union of carbon and nitrogen, and which combines 
with potassium, reduced from the potash by the action of 
the carbon, forming cyanide of potassium. If irpn be pre- 
sent in the mixture of fused cyanide, it is taken up on treat- 
ing the mass with warm water, forming ferrocyanide ; the 
iron being dissolved very readily, whether existing as metal- 
lic iron, oxide or sulphuret. Animal matter, when mixed 
with fused potash according to the old process for the manu- 
facture of prussiate, yields both the carbon and nitrogen 
necessary for this reaction. It has long been known to 
chemists that a similar effect occurs when gaseous ammo- 
nia is passed through charcoal impregnated with potash and 
heated to redness. This was the method by which Scheele 
confirmed synthetically, his original analysis of hydrocyanic 
acid. Within a few years past it has been discovered that 
the same results ensue when atmospheric air is passed 
through a similar mixture, and as this latter is of course 
the cheapest of all the sources of nitrogen, it is desirable 
to ascertain a practical and available method of applying 
it for this important manufacture. 
Mr. L. Thompson, of Lambeth, England, is said by Ure 
to have been the first to apply the principle of the formation 
of cyanides from atmospheric air, practically. His method 
is to expose at a red heat a mixture of two parts each of 
coke and carbonate of potassa, and one part iron turnings 
in a shallow pan for some lime, frequently stirring. There 
is certainly some formation of cyanide by this method, 
which we have frequently repeated, but, according to our 
experience, the proportion is insignificant, and it will not 
answer for the manufacturer. 
