It may happen that the quantity of the above substances is not
sufficient to allow their metallic reduction by calcination. In that
case, we must proceed to obtain a solution; but since neither the oxide,
nor the carbonate, is soluble in water, it will be necessary to bring
them in contact with concentrated acetic acid, so as to obtain an
acetate of copper; which will furnish the following indications with the
respective tests.
_a._ _A surface of clean iron._ If dipped into the solution will become
coated with metallic copper, and appear as if transmuted into that
metal.
_b._ _Ammonia._ This test, when added in a quantity more than sufficient
to saturate any excess of acid, will strike a beautiful blue colour; in
the first instance we shall obtain a deep blue precipitate, but this
will be redissolved by an excess of alkali. To detect the presence of
copper, therefore, in pickles, it is only necessary to cut them into
small pieces, and to pour liquid ammonia, diluted with an equal bulk of
water, over them in a stopped phial: if the pickles contain the most
minute quantity of this metal, the ammonia will assume a blue colour. In
the same manner cupreous impregnations may be discovered in the various
articles of confectionary above enumerated, and in those foreign
conserves which are imported into this country, and usually sold in
round boxes.
_c._ _Sub-carbonate of Potass._ By this re-agent a precipitate of a pale
blue colour is produced.
_d._ _Arsenite of Potass_ instantly occasions a copious precipitate in
the acetate of copper, which is of a green colour, and is in fact an
arsenite of the metal.
_e._ _Triple Prussiate of Potass._ This test gives a brown precipitate
with a solution of verdegris, which is found to consist of prussiate of
copper, and prussiate of iron; while the liquor contains an acetate of
potass.
2. _The suspected poison is mixed and combined with various alimentary
substances._
We have in this case the same embarrassments to encounter, as those
already noticed under the consideration of arsenic. Our tests may
produce their respective precipitates, but they will present different
colours according to the nature of the fluids with which the substance
happens to be mixed; whence the circumstance of colour, so
characteristic on other occasions, cannot be received as a satisfactory
indication. In such a difficulty, we may collect the precipitates, and
calcine them in a crucible with charcoal, in order to obtain the metal;
or we may at once evaporate the whole of the alimentary mass, and submit
it to a high temperature, by which means all the vegetable and animal
principles, which can form a part of the liquor vomited, will be
decomposed and converted into several volatile productions, and into
charcoal; this combustible body will decompose the oxide of copper, and
reduce it to its metallic state.[312].
Nor is this process without its fallacies; it is often difficult to
recognise the metal, dispersed as it necessarily must be, in small
quantity, through a considerable mass of charcoal; in this case we are
recommended by _Orfila_ to place the product of the calcination in
water, when in a short period, the copper, from its superior specific
gravity will subside from the lighter particles of charcoal. But it
would be still better to pour nitric acid upon the product of the
calcination, and thereby to obtain a solution of _nitrate of copper_,
which by filtration might be immediately prepared for the application of
appropriate re-agents.
It merits notice, however, that in certain cases of poisoning by copper,
no vestiges of the substance can be found in the matters voided from the
stomach. In that case, _Orfila_ directs that the mucous membrane of the
stomach, and of the intestines, should be scraped off, dried, and
submitted to the action of a strong heat in a crucible. “I have,” says
this distinguished experimentalist, “twice obtained metallic copper, by
calcining in this manner a portion of the membranes of the stomach of
two dogs that I had poisoned with verdegris. This effect particularly
takes place when the mucous membrane is of a bluish colour, hard, and
strongly adhering to the substance of the stomach.”
TIN and its MURIATE.
It is clearly established by the experiments of _Bayen_ and
_Charlard_,[313] as well as by those of _Proust_,[314] that this metal
possesses no poisonous properties. Its muriate, however, has been shewn
by _Orfila_ to possess highly corrosive properties. It excites violent
vomiting, great depression, and death, without convulsions. Its antidote
is milk, which it speedily coagulates; and by chemical combination with
it, the poison is rendered inert. On dissection, the stomach is said to
have been found corrugated and indurated, and has been compared to
tanned skin, but its colour is not altered.
As this substance is never likely to become an object of forensic
interest, in this kingdom, we shall pass it over without farther notice.