Note 422 — PHARMACOLOGIA. (continued 2)

Dr. Bostock confesses that where less than three-fourths of a grain were used, he could not say that the metallic crust was clearly perceptible; and Dr. Black considered that one grain was the smallest quantity which could be distinctly recognised by such a process. Dr. Jaeger (Dissertatio Inauguralis, Stuttgard, 1808) also 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! I must be allowed to question this fact; Dr. Jaeger, no doubt, believed that he recognised the alliaceous odour, but it must have been the effect of imagination. Dr. Bostock observes that, if Arsenic be mixed with either an animal or vegetable substance, the smoke and smell arising from those bodies, when heated, will altogether prevent our recognising its odour. He found that when a quantity of Arsenic was 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 arose from the latter could be alone perceived; nor was it possible to discover that any thing had been mixed with it (Edinb. Med. Journal.) This objection of Dr. Bostock is true in fact, although it admits of a different explanation, for at a low temperature the Arsenious acid would be volatilized without decomposition; in which case no alliaceous odour can be developed. Dr. Traill has lately asserted (Annals of Philosophy, Feb. 1824) that he has recognised the alliaceous odour during the volatilization of 1/78th of a grain of the metal. I do not question the truth of this assertion, but there must have been an address in the manipulation which we cannot expect to find in ordinary experimenters.