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.