638 COPPER—VERDIGRISE—DECOMPOSITION OF
Verdigrise is an acidulous oxyd or rust of copper, produced by art,
prepared much in the fame manner as the saccharum saturni. It is
also prepared in a coarser way, by taking what remains in the wine
press, after the must has been entirely squeezed from the grapes, add
ing some soured wine, and stratifying this mixture with plates of cop
per. As the huſks grow sour, the copper is corroded; and after some
weeks of this treatment, the faline crust is beaten off by the hammer.
This coarse preparation is then diffolved in weak vinegar, with the
addition of some more copper ; and lastly the crystals are purifyed in
the usual manner.
This substance diffolves readily in distilled vinegar, and gives a li
quor of a deep green, which being evaporated, gives crystals of the
fame colour ; but the powder of them is bright and elegant, like that
of all semi-transparent bodies. Hence it is used by painters, though
they find it corrofive. The name they give it is very improper,
distilled verdigrise.
All these compounds of copper with acids, when they are thrown
into the fire, or mixed with flaming fuel, give a green or blue colour
to the flame, and noxious fumes.
If we desire to decompound these compounds of copper with acids,
we can effect the decomposition of some of them by heat alone, others
can scarcely be decompounded without the aid of an elective attrac
tion.
The one which is the moſt easily decompounded by heat alone, is
the acetite of copper. This must be done by distillation of the dry
materials, that we may obtain the acid as concentrated as possible. As
a dry powder cannot communicate the heat so quickly and perfectly
to the interior parts, as a fluid body can do, this distillation always
destroys some of the acetous acid. The first part of the produce is
tainted with a ſmall portion of copper, which gives it a green colour;
and before the production of acid vapours is much abated, there is a
very fensible empyreuma. We therefore do not obtain nearly the