The arsenite of copper [Scheele’s-green, Mineral-green] deserves notice,
because it is in use as a pigment, and has actually been used as a
poison. Dr. Duncan once detected it in pills, given to a pregnant female
with the view of procuring abortion; in Paris it has been detected in
sweetmeats, having been used to give them a fine green colour;[556] and
Mr. Ainley of Bingley in Yorkshire informs me he found it to constitute
a pigment sold by London pastry-cooks under the name of emerald-green
for colouring preserves, and which in his practice had proved poisonous
to children who had eaten apple-tarts coloured with it.
It is a compound of arsenious acid and deutoxide of copper, is sold in
powder or pulverulent cakes, and has a pale grass-green colour. Its
nature may be ascertained by heating it in a glass tube. Crystals of
oxide of arsenic sublime, and oxide of copper remains, which, on being
dissolved in nitric acid, yields a fine violet-blue solution with
ammonia.
The mineral-green of the shops, however, is seldom arsenite of copper.
The substance sold in Edinburgh under that name, although believed by
colourmen to be a preparation of arsenic, is not the arsenite of copper,
but a mixture of hydrated oxide of copper and carbonate of lime; which
will be mentioned more particularly under the head of the poisons of
copper.
_Process for Organic Mixtures._—The suspected mixture is to be heated
with a little hydrochloric acid and well stirred. The arsenite being
thus dissolved, the solution is to be allowed to cool and then filtered.
A stream of hydrosulphuric-acid gas will now cause a dark-brown or
yellowish-brown muddiness or precipitate, which is a mixture of
sulphuret of copper and sulphuret of arsenic. The precipitate being
separated after boiling, and properly cleansed by the process of
subsidence and affusion, or if it is large, by washing on a filter, the
two sulphurets are to be separated by ammonia, which dissolves sulphuret
of arsenic but leaves the sulphuret of copper; and the sulphuret of
arsenic may be recovered from the filtered fluid by expelling the
ammonia with heat. The sulphuret of arsenic is next to be reduced as
directed at page 211; and the sulphuret of copper examined as
recommended under the head of copper.