By oxidation, copper becomes poisonous. The substance may be easily
recognised by the change of colour which it produces in ammonia; this
alkali will dissolve it instantly, and assume a beautiful blue colour.
It is wholly insoluble[308] in water. In oils and fatty matter it is
easily and copiously dissolved at the ordinary temperature of the
atmosphere. Such bodies also, when boiled in vessels of perfectly clean
copper, facilitate their oxidation, especially if left to cool a few
minutes before they are poured out.
GREEN CARBONATE OF COPPER—_Natural Verdegris_.
This substance forms spontaneously on surfaces of copper and brass; it
differs from the oxide in its green colour, and in effervescing with
dilute sulphuric acid; with ammonia, however, it demeans itself in the
same manner, and is likewise insoluble in water. It is poisonous.
From the above history of these substances the medical practitioner will
easily perceive under what circumstances, and by what bodies, metallic
vessels of copper may be rendered dangerous. The oxide and carbonate,
formed in them, will easily dissolve in acidulous and oily aliments,
whence it follows that all preparations of such food, if conducted in
vessels whose surfaces have contracted this change will be liable to
prove deleterious.[309] If the vessels be perfectly clean, acid
preparations may be safely boiled in them, but they must be poured out
immediately, and not suffered to remain sufficiently long to allow the
copper to become oxidized. To the formation of the oxide of copper, and
to the acetic acid contained in the wine, vinegar, beer, and cider, _M.
Orfila_ attributes the production of the _acetate_ which forms about the
corners of the cocks in vessels containing these liquors. Upon the same
principle the _soda water_ sold in this town, in a draught, from the
pump, is liable to metallic impregnation, as we have fully satisfied
ourselves.
Equally important is it for the forensic physician to be acquainted with
the various other sources from which copper poison may be derived. In
consequence of the fact of the oxide of copper forming, with the acids,
compounds of a beautiful green colour, the metal is often employed in
cookery to impart a vivid hue to various articles; the sale of pickles,
for instance, frequently depends upon the liveliness of their green
colour; whence we find, in works[310] on cookery, directions for
ensuring such an effect, by boiling the pickles with copper coin, or by
suffering them to stand for some time in vessels of that metal. In the
third volume of the _Medical Transactions of the College of Physicians_
we shall find an interesting history, related by _Dr. Percival_ of
Manchester, of a young lady who amused herself, whilst under the hands
of the hair-dresser, with eating pickled samphire, of which she consumed
two breakfast plates full; she shortly afterwards complained of great
thirst, pain in the stomach, and a rash appeared upon her hands and
breast. After an illness of nine days, during which she suffered severe
vomitings, and tormina of the bowels, she expired. Upon examining the
samphire, _Dr. Percival_ found that it was very strongly impregnated
with copper. In the preparation of confectionary, especially
sugar-plums, and sweatmeats of a green colour, copper is very generally
introduced, and many instances are recorded of their having proved
highly deleterious. Catsup is also said to be occasionally impregnated
with verdegris; and vestiges of this metal have been detected in the
well known cordial, called _Shrub_.
In order to prevent the _contingent_ dangers attendant upon copper
vessels, they ought always to be _tinned_;[311] and it is a very curious
and interesting fact, that this latter metal, although it may cover the
copper surface only imperfectly, will nevertheless protect us from its
effects; for _M. Proust_ has shewn that the superior readiness with
which _tin_ is oxidized and acted upon by acids, when compared with
copper, will not allow this latter metal to appropriate to itself a
single atom of oxygen.
But copper vessels, notwithstanding this fact, unless well tinned,
should be dismissed from the service of the kitchen. The Senate of
Sweden, in the year 1753, prohibited them entirely, and ordered that
none but such as were made of iron should be used in their fleets and
army.