298 
CYANIDE OF POTASSIUM. 
results, that from live atoms of ferrocyanide of potassium, 
which contains thirty atoms of cyanogen, there cannot be ob- 
tained more hydrocyanic acid than from nine atoms of cya- 
nide of potassium, viz.: eighteen atoms of hydrocyanic acid, 
the other twelve atoms remaining with bluish white ferru- 
ginous precipitate. 
If the ferrocyanide of potassium be converted into cyanide 
by the method indicated, there may be obtained from five 
atoms of ferrocyanide, twenty-five atoms of hydrocyanic acid, 
consequently seven atoms more. 
For the decomposition of one atom of ferrocyanide, one 
atom of sulphuric acid is usually directed, which suffices to 
form with the potassa an acid sulphate of potassa: in using 
the cyanide there is required but one atom of acid. 
Equal parts of hyd rated sulphuric acid and cyanide of po- 
tassium are the best proportions for the preparation of hydro- 
cyanic acid; the sulphuric acid suffices to form with all the 
potassa a neutral sulphate and an acid sulphate of ammonia 
with all the ammonia produced by the decomposition of the 
cyanate of potassa. The cyanide is to be dissolved in double 
its own weight of water, and the sulphuric acid, diluted with 
three times its weight of water, is to be gradual^ added in 
small portions, allowing the effervescence produced by each 
portion to subside previous to the addition of another. 
Preparation of Cyanate of Potassa. 
Cyanide of potassium, prepared by the method just indi- 
cated, offers an excellent means for preparing the cyanate. 
To prepare this salt, common litharge, which has been pre- 
viously heated red hot, should be preferred. The cyanide 
being fused in a Hessian crucible, pulverised litharge is gra- 
dually added ; the oxide of lead is reduced, and the metal re- 
mains in the form of powder mixed with the cyanate formed; 
by an increase of the heat it is fused into button. The fused 
mass, which is nothing else than cyanate of potassa, is poured 
out, reduced to powder, and boiled with alcohol as often as it 
