A. Treat the filtered liquid with carbonate of potass.
B. Add a solution of sulphate of iron with a small quantity of alum: a
precipitate, as in the former method, will fall down, which if
treated by free sulphuric acid, will also become blue and
pulverulent. During this latter part of the experiment, there is a
disengagement of carbonic acid.
Evidence may be pushed still farther, and the existence of the Prussic
acid proved in a most positive manner by decomposing the precipitate,
above described, and which is a true Prussian blue, so as to separate
the acid. For this purpose, heat the precipitate with an equal quantity
of tartaric acid, in a glass retort, at the temperature of 150°, when
the hydro-cyanic vapours will soon exhale from the mixture, and may be
received in water.”[442]
Cl. V. NARCOTICO-ACRID POISONS.
We have already stated our objections to this division, and our apology
for adopting it. _See page_ 205.