This metal, with the exception of gold and silver, and perhaps tin, was
known earlier than any other metal; but its applications were entirely
confined to the arts. It was first discovered by the Greeks in the
island of Cyprus, whence its name; and we learn from _Homer_, that even
during the Trojan war, the combatants had no other armour but what was
made of bronze, which is a mixture of _copper_ and _tin_.[305].
The external characters of the metal are too well known to require
minute description. Its taste is styptic and nauseous; and the hands
when rubbed for some time on it, acquire a peculiar and disagreeable
odour. When melted, its specific gravity is 8·667; but after being
hammered it is 8·9. It is only susceptible of two degrees of oxidation.
If the protoxide be _native_, it is red; if _artificial_, orange
coloured. The peroxide is black.
Copper, on exposure to a moist atmosphere, becomes tarnished, absorbs a
portion of its oxygen, and passes into the state of an oxide, which
shortly unites with the carbonic acid of the atmosphere, and forms a
greenish carbonate of copper.
Metallic copper, perfectly pure, does not possess any deleterious
properties. We have already cited instances[306] sufficiently conclusive
to establish this fact. It becomes, therefore, a subject of no little
interest to enquire, under what circumstances it may become poisonous by
combination. _M. Orfila_ observes that it has been long maintained, that
milk heated, or allowed to remain in vessels of copper not oxidized,
dissolved a portion of this metal, and acted as a poison. _Eller_, a
philosopher of Berlin, has, however, very clearly proved such an opinion
to be incorrect. He boiled in succession, in a kettle well freed from
verdegris, milk, tea, coffee, beer, and rain water; after two hours
boiling, he found it impossible to discover, in any of these fluids, the
least vestige of copper. _M. Drouard_ has also shewn that distilled
water, left for a month together on the filings of this metal in a glass
bottle, did not dissolve an atom of it. The celebrated toxicologist
above cited, after relating these important facts, concludes by
observing, that the phenomena are very different, if, instead of pure
water, we substitute that which contains a certain quantity of muriate
of soda. _Eller_ has demonstrated the presence of a very small quantity
of copper in water, which contained 1/20th of its weight of muriate of
soda, and which had been boiled in a brass kettle. This fact is of the
highest importance, for it will explain the reason why highly seasoned
aliments have proved deleterious, when cooked in vessels of copper. But
we are indebted to _Mr. Eller_ for a still more important discovery; he
found that if, instead of heating a simple solution of common salt in
copper vessels, the salt be previously mixed with beef, bacon, and fish,
the fluid resulting from it does not contain an atom of copper.[307] In
relating this fact, _M. Orfila_ observes, “however astonishing it may
appear, it is quite correct, _M. Eller_ was the first to announce it,
and I have several times ascertained the truth of it; it is probable,”
continues _Orfila_, “that the combination of several kinds of aliments
destroys the effect of the solution of the muriate of soda; which
consequently ought to render the cases of poisoning by aliments cooked
in copper vessels, _which are not oxidized_, extremely rare.”
Copper combines with sulphur, and affords a black sulphuret.