CYANIDE OF POTASSIUM. 
297 
five atoms of cyanide, and consequently one-fourth more than 
by fusion at a red heat. The cyanate of potassa, with which 
it is mixed, does not injure it for any of its uses. It is rea- 
dily detected by supersaturating the cyanide with an acid; 
effervescence then results from the disengagement of car- 
bonic acid, and an ammoniacal salt is found in the liquid. 
The explanation of the formation of cyanide of potassium, 
under the conditions indicated, is not strictly exact; for the 
carbonate of the protoxide of iron, which is formed, is decom- 
posed previous to reduction into carbonic acid and black 
oxide of iron; and at the expense of this latter there is formed 
an indeterminable quantity of cyanate of potassa, over and 
above that indicated by the preceding formula. 
The metallic iron remaining, as well as the sides of the 
crucible, is covered with cyanide of potassium; to obtain this, 
the most advantageous process consists in dissolving from 
the crucible, by warm water, every thing soluble, and heat 
the solution with a little sulphuret of iron, which is readily 
dissolved. 
From this solution the ferrocyanide may be obtained by 
evaporation ; and the mother waters contain sulphuret of 
potassium. 
Preparation of Hydrocyanic Acid. 
The cyanide is much superior to the ferrocyanide of potas- 
sium for the preparation of hydrocyanic acid, because the 
product is more abundant, and the distillation is conducted 
with more facility. 
In the distillation of ferrocyanide of potassium with sul- 
phuric acid, there is deposited a bluish white powder, a com- 
bination of cyanogen, potassium and iron, analogous, in com- 
position, to the ferrocyanide of zinc, and is expressed by the 
following formula: 
3Cf y+3Fe^ cr y = c y 6Fe -) 
From the formation and composition of this body there 
