The Sun.
London, England, 1844-10-09 00:00:00

POISONS.--THEIR TESTS AND
ANTIDOTES.
At the Royal Polytechnic Institution, yesterday, Dr.
Ryan delivered a lecture upon the important subject of
poisons, mineral, vegetable, and animal—and the various
modes of discovering their presence and of counteracting
their effects in an animal body. He observed, that it was
in the highest degree desirable that tome knowledge of
poisons, and the signs of their presence, should be pos-
sessed by every person who might be called upon to give
evidence, or deliver judgment, as to :he guilt or innocence
or a fellow-subject accused of committing murder by the
most common and insidious means. Having explained,
in a popular manner, and illustrated by simple experi-
ments, the principles of chemical analysis, especially
the formation of precipitates, by the colour of which the
material held in solution is detected, the lecturer chose
arsenic as his first subject, on account of its extensive
use. lle exhibited specimens in the solid form, and con-
demned the imprudence of selling, in the public shops,
without any precaution, so deadly a substance, which,
from its colour and appearance, might be mixed, without
detection, in flour, arrow-root, and other innocuous
white powders, from which, when separate, it is dis-
tinguishable only by the weight. There was a means
of rendering arsenic easily distinguishable without im-
pairing its utility in the arts or its efficacy in the de-
struction of vermin. If three or four per cent. of prus-
siate of potass and sulphate of iron be added, when
placed upon chalk, a blue colour will indicate the pre-
sence of arsenic. This we understood him to recommend
as a precaution in the public sale of the drug. But as a
test to discover its presence amongst other substances,
Marsh's test properly applied would discover the five-
thousandth part of it. At considerable length, and by
various beautiful experiments, he pointed out the falla-
cies of the liquid tests, which were too much relied on,
and often too loosely applied. Zinc and sulphuric acid
both contained arsenic, and unless the chemist were very
careful in applying them he might place the life of an inno-
cent fellow-creature in jeopardy. This risk might be avoided
by taking sufficient care to secure the purity of the tests
themselves. Here he mentioned incidentally that pure
water in passing through lead pipes becomes impregnated
with a powerful poison, the carbonic acid evolved from
the water combining with the lead to form carbonate of
lead. This combination does not so readily take place
when the water is impure, encrustations forming on the
surface of the pipes and preventing the contact of the
water with the lead. Dr. Ryan then illustrated the falla-
cies to which the hydro-sulphuric acid may lead. The
experiment was very interesting, and elicited much ap-
plause. On the table were placed six glasses,
each containing a perfectly colourless fluid.
The first contained an arsenical solution ;
the second antimony in solution, the third cadmium (a
metal found in small quantities with zinc), the fourth
tin, the fifth selenium, and the sixth zinc. To each of
those in succession a few drops of hydro-sulphuric acid
were added, and the effect was such as ought to warn the
inexperienced analyst against giving too positive an
opinion upon the faith of his tests. The acid with the
arsenic produced a bright yellow, the orpiment of the
shops. With the antimony, the compound was nearly
of the same colour, only rather more orange, but easily
mistaken for the former, when not compared with it in
juxta-position, unless the observer have a very exact
memory of colours. The four remaining compounds
were so nearly of the same colour, that where the
quantities are very small, any of the five might be mistaken
for an arsenical compound, unless by a person ofvery rare
experience and accurate eye. Fatal error in such a case
might be avoided by adding ammonia when the arsenic,
if present in the precipitate, would be re-dissolved. It
would exceed our limits to follow the learned Professor
through the details of this highly valuable discourse, but
we will content ourselves with giving his account of the
antidote most to be relied upon in cases of poisoning by
arsenic. It is the hydrate peroxide of iron, which is
formed by boiling a solution of copperas in nitric acid,
and adding ammonia, when the peroxide is precipitated.
This combines immediately with the arsenious acid in
the stomach, and forms a neutral salt, which is in-
noxious.

This course of lectures commenced with arsenic, because
that poison is the most easily obtained, and the most
frequently resorted to for the purpose of suicide or do-
mestic murder ; and whilst it is of importance to discover
its actual presence, it is also important to guard against
presuming its discovery where it is not. The next sub-
ject will be that of prussic acid, the antidotes to which
formidable poison are much more accessible than that for
arsenic.