2nd. To another portion of the liquid, the ammoniaco-nitrate of silver was added; a slight turbidness arose, but no yellow precipitate occurred.
3rd. After adding a fixed alkali, the surface of the liquid was touched with a stick of lunar caustic, but no yellow precipitate was produced.
4th. The liquid was next assayed in a watch-glass, for a phosphate of soda, by endeavouring to form a triple salt with magnesia and ammonia, as suggested by Dr. Wollaston; the result proved that phosphate of soda was not present. It is unnecessary to pursue the relation of the experiments; I conceive that sufficient evidence has been adduced to establish the truth of the explanation. I have frequently repeated the first experiment, substituting for the gastric infusion, a decoction of onions, and with similar results.
[419]. This explanation applies equally to the objection lately advanced by Dr. Porter, of the University of South Carolina, who in observing on the tests for arsenic, remarks, that an appearance similar to Scheele’s Green, is produced by the carbonate of potass when added to a solution of copper containing coffee, but without arsenic, more striking than if a weak solution of arsenic be used. Silliman’s Journal, iii. 365.
[420]. Annals of Philosophy, New Series, No. III. for March, 1821.
[421]. The habitudes of arsenious acid with the nitrates were first observed by Kunkel; nitrous vapour is disengaged, part of the oxygen being absorbed by the arsenious acid, by which an arsenite of potass is formed.
[422]. 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.
[423]. Assafœtida was used by the ancients as a condiment, under the name of σιλφὶον, Laserpitium, (Pliny); and according to Kempfer, the Persians use it for the same purpose. The Arabian writers on the materia medica class this article among their Mobehyat (Aphrodisiaca). The term Assafœtida is derived from the monks of the Salernian school; some of the writers of the middle ages call it Opium Cyrenaicum, i. e. the Juice from Cyrene.
[424]. Tolu Lozenges. Sugar 8 oz. Cream of Tartar 1 oz. Starch 2 drachms. Tinct. Toluiferæ Balsami E. one fluid-drachm, mucilage of Gum Tragacanth q. s.
[425]. Belladonna, so called from the juice of its berries being used as a cosmetic by the Italian women, to make their faces pale.