the retort speedily turns to one of the blues, identical with,
or allied to, Prussian blue. This is at best a disagreeable
process to conduct, for the hydrocyanic acid formed
adheres so strongly to the glass, that, instead of being
freely given off, bubbles are evolved suddenly with such
explosive violence as occasionally to crack the vessel.
This may be remedied as far as possible by the insertion
of plenty of waste pieces of platinum--if platinized,
so much the better, as that facilitates 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.