The Sun. — 1844-10-09 (London, England)

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 possessed 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 experiments, 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 condemned 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 distinguishable only by the weight. There was a means of rendering arsenic easily distinguishable without impairing its utility in the arts or its efficacy in the destruction of vermin. If three or four per cent. of prussiate of potass and sulphate of iron be added, when placed upon chalk, a blue colour will indicate the presence 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 fivethousandth part of it. At considerable length, and by various beautiful experiments, he pointed out the fallacies 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 innocent 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 fallacies to which the hydro-sulphuric acid may lead. The experiment was very interesting, and elicited much applause. 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 innoxious.  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 domestic 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 subject will be that of prussic acid, the antidotes to which formidable poison are much more accessible than that for arsenic.