orence flasks,
answer well: a bent tube being connected at one end to its month, the
other passing into the second vessel; heat should be cautiously applied
by means of an Argand lamp, a little vessel of sand being placed under
the flask, which helps the acid to decompose the salt. 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 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