Arsenic, Trii′odide of

AsI 3 . Syn. Teriodide of arsenic , Iodide of arsenic ; Arsen′ici iodi′dum , A. teriodi′dum , L.; Arsenic iodure , ., Fr. Prep. 1. From finely-pulverised metallic arsenic, 2 parts; iodide, 11 parts; mixed and gently heated in a bent gla tube, or a suitable retort, until combination is complete; the heat being then raised, and the sublimed iodide collected, and at once put into a well-stopped phial. 2. Arsenic, in fine powder, 1 part; iodine, 5 parts; triturate them together, place the mixture in a small flask or retort just large enough to contain it, and apply a gentle heat until liquefaction is complete, avoiding the formation of iodine vapour; when the odour of iodine is no longer perceptible, and the ma a umes a reddish-yellow colour and crystallises on the sides of the ve el, the operation is complete, without having recourse to sublimation. A very easy and excellent proce . Prop., . A deep orange-red, crystallisable solid; soluble in water, and highly volatile and poisonous. Its aqueous solution yields the iodine unchanged by rapid evaporation, but when slowly concentrated and set aside, white pearly plates are obtained, consisting of arsenious acid and the teriodide. As a medicine it combines the properties of both arsenious acid and iodine, but its use requires great caution. It has been succe fully employed by Dr A. T. Thomson, Biett, and others, in obstinate skin diseases (lepra, impetigo, herpes, lupus, psoriasis, .), and in real or stimulated cancer.— Dose , 1 ⁄ 16 to 1 ⁄ 12 gr. (in pills or solution), gradually increased to 1 ⁄ 6 or even 1 ⁄ 3 gr. (A. T. Thomson.) Externally, 2 1 ⁄ 2 gr., to lard 1 oz.; of which 1 dr. may be used at a time. (Biett.)