the escape of the
gas. The heat should be applied to every part of the vessel, and the
flame should not be allowed to play upon one single part alone. Large
commercial operations are performed in green glass or stone-ware
retorts.

"Now for one word of advice to the tyro: Remember that you are working
with prussic acid; therefore, never conduct the process in a room, the
fumes being quite as poisonous as the solution of the acid itself;
moreover, have always a bottle of ammonia or chlorine by your side,
that should you have chanced to inhale more than is pleasant, it will
be instantly at hand to counteract any bad effects. It is stated by
Pereira, that a little sulphuric acid or hydroferrocyanic acid passes
to the outer vessel, but probably the amount would be of no consequence
for electro-metallurgy, otherwise, it might be as well to use a
Woulfe's apparatus, and discard the salt formed in the first vessel.
To the large manufacturer it may be worth considering whether some
other metallo-cyanuret, formed in a similar manner to the
ferrocyanuret, might not be more advantageously employed, because the
residue of the process last described contains a large quantity of
cyanogen which the acid is unable to set free.

"There are other modes of procuring prussic acid, besides the one which
has been so tediously described; but these are found to be more
expensive. The only one which I shall now notice is the process by
which it is obtained from bicyanide of mercury. The bicyanide of
mercury itself is formed when peroxide of mercury is digested with
Prussian blue, the peroxide of mercury abstracting the whole of the
cyanogen from the blue, and leaving the oxides of iron at the bottom of
the vessel. The solution may be evaporated to dryness, and one part of
the salt dissolved in six of water; one part of muriatic acid, sp. gr.
1.15, is then added, and the solution distilled, when the whole of the
hydrocyanic acid passes over, and by being conducted into a solution of
potassa, as in the former process, forms cyanuret of potassium. This
process, though easier than the first described, is rather given as a
resource under peculiar circumstances than as one to be adopted by the
large manufacturer. The expense is the only objection, but in a small
quantity this cannot be a consideration.

"In giving this very rough outline of the general mode of forming
salts, the minutiae necessary for chemical work have altogether been