Note 246 — MINERAL POISONS.

Foderé recommends this process, Traité de Med. Leg. t. iv, p. 153; and Dr. Jaeger, in his Thesis, before quoted, observes that he has been enabled to recognise the tenth of a grain of arsenious acid, although mixed with sugar, by its odour, when thrown upon burning coals! We must be allowed to question this fact; Dr. Jaeger, no doubt, believed that he recognised the alliaceous odour, but it must have been the sole effect of the imagination. Dr. Bostock states that such a test is not to be depended upon; for, unless the arsenic be in considerable quantity, the odour is not sufficiently perceptible; and if it be mixed with either an animal or a vegetable substance, the smoke and smell arising from these bodies, when heated, will altogether prevent our recognising the peculiar odour of the arsenic. When a quantity of arsenic is mixed with an equal weight of flour, and placed upon iron at a low red heat, so as not to cause the flour to inflame, the suffocating smoke that arises from the latter can be alone perceived; nor is it possible to discover that any thing has been mixed with it. Edinb. Med. Journ. l. c. This last objection of Dr. Bostock is true in fact, although it admits of a different explanation, for at a low temperature the arsenious acid will be volatilized without decomposition; in which case no alliaceous odour can be developed.