Prussic acid is then generated and passes through the tube to
the recipient vessel, which is to be charged with liquor potassae.

"When the potash is saturated, the operation is completed.
The Germans recommend a strong, alcoholic solution of potassa
to be used in the second vessel, for in this case, the hydrocyanic
or prussic acid combines with the potassa, forming a hydrocyanate
of potassa, or, the water being abstracted, the cyanuret
of potassium, which spontaneously precipitates, on the saturation
of the fluid, the cyanuret, being insoluble in strong alcohol.
The ferrocyanate of potash may be considered as containing
three equivalents of hydrocyanic acid, two of potash and one
of iron; but, unfortunately, we can only obtain half the acid
from the salt, owing to the formation of a compound during
its decomposition which resists the action of the acid.
The decomposition of this salt taking 2 equivalents or 426 grains
(to avoid fractions) would afford 3 equivalents or 81 grains
of hydrocyanic, or prussic acid, capable of forming 198 grains
of cyanuret of potassium, while in the retort there would
remain 384 grains or 3 equivalents of bisulphate of potash,
and 1 equivalent or 174 grains of a peculiar compound,
said to contain 3 equivalents of cyanogen, 1 of potassium,
and one of iron (Pereira). It is manifest that, but for this
later compound, we might double the quantity of hydrocyanic
acid from the yellow salt."

The decomposition just described is the one usually received;
but too much reliance must not be placed on its accuracy,
for the analysis of the several compounds is too difficult
for the results to be fully admitted. The residue left in