ARSENIOUS ACID.

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alcohol or oil on the surface of the liquid in the short limb, and placingthe apparatus aside for an hour or two, to allow the bubbles to burst.

The fallacy of the test is, that if a solution of emetic tartar be em-ployed instead of an arsenical liquid, we obtainFig. 04. antimoniuretted hydrogen gas, which coincides in

many of its properties with arscniuretted hydrogen(Mr. L. Thompson, Land, fy Edinb. Phil. Mag.,May 1837). Thus it has a peculiar odour, not veryunlike that of arseniuretted hydrogen, and bums inthe air with a pale bluish flame, and the depositionof metallic antimony and the white oxide (onmica or glass held over it), which resemble, in theirgeneral appearance, arsenicum and arsenious acid:moreover, the action of hydrosulphuric acid andof ammoniaco-sulphate of copper on the oxide ofantimony, produces colours resembling those generated by the action ofthese tests on arsenious acid. The two metals may, however, be dis-tinguished by adding a drop of nitric acid to the crusts, and evaporat-ing to dryness : a white powder is left in each instance. A few drops ofa dilute solution of the nitrate of silver being now added, and the wholeexposed to the fumes arising from a stopper moistened with ammonia,the arsenical crust will give the well known canary-yellow flocculi (Mr.L. Thompson, op. cit.) Moreover, the greater volatility of arsenicum,and its conversion into octahedral crystals of arsenious acid (Dr. E. Tur-ner’s Chemistry, by W. Turner ) may serve, in some cases, to distinguishit from antimony. Furthermore, the solubility of the arsenious acid, andthe reaction of the before-mentioned liquid tests on the solution, will dis-tinguish it from oxide of antimony, which is insoluble.

In performing Marsh’s test great care must be taken that the apparatusbe perfectly clean, and that fresh zinc and acid liquor be used for everyexperiment. The experimenter should be fully alive to the possibility ofthe acid, zinc, or even the brasswork of the apparatus, containing minutetraces of arsenic; hence the necessity of examining the qualities of thehydrogen flame before adding the suspected arsenical liquid. It has beenshown by Mohr ( Journ. de Pharm. xxiii. 563) that zinc which had beenonce used, but afterwards carefully washed both in water and acid, retainedsufficient arsenic to produce the usual effects on the hydrogen flame.

3. Of Arsenious Acid in Organic Mixtures. —I shall confinemyself to a brief notice of the modes of detecting arsenious acid whenmixed with the" contents and tissues of the stomach, and must refer thereader to Dr. Christison On Poisons, and to his paper in the Edinb.Med. &; Surg. Journ. xxii. 60, as well as to Devergie’s Med. Leg. ii. 718,for further details, especially in reference to other organic mixtures.

When the stomach is laid open we sometimes observe in it a whitepowder or white particles; these are, of course, to be carefully removed;and if they be arsenious acid, no difficulty will be experienced in recog-nising them by the tests already mentioned.

If no solid arsenious acid be observed, cut the stomach into smallpieces, and boil it with the contents of this viscus for half an hour indistilled water, to which a small quantity of liquor potass® has beenadded: then filter, first through muslin, and afterwards through paper.Fibrin is insoluble in water, and, by boiling, albumen is coagulated, so