part in. Metallic Preparations. — Arsenic.

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the white oxide can be employed. (See Arsenici Oxydum, Partii.) It was introduced by Dr. Fowler as a substitute for thecelebrated empirical remedy known under the name of " theague drop," which owes its efficacy to the oxide of arsenic.In addition to the account we have already given of the medi-cinal use of the oxide, we have to add that we have given thissolution with decided advantage after cupping and purging, inthreatened apoplexy when the strength was little and the com-plexion pale. The dose is V{ iv gradually increased to TH. xx,given twice a day.

ARSENIAS KALI. Dub. Arseniate of Kali.

" Take of white oxide of arsenic, nitrate of kali, eatch anounce. Reduce them separately to powder; then having mixedthem, put them into a glass retort, and place it in a sand-bathexposed to a gradually raised heat, until the bottom of the re-tort becomes obscurely red. The vapours arising from the re-tort should be transmitted through distilled water, by means ofa proper apparatus, in order that the nitrous acid extricatedby the heat may be disengaged. Dissolve the residue in fourpounds of boiling distilled water, and after due evaporationset it apart, that crystals may form."

In this process the nitrate of potash is decomposed by theheat; part of the oxygen of the nitric acid with the whole ofits nitrogen escape in the form of nitrous gas, while the re-mainder of the oxygen is attracted by the oxide of arsenic,which is thus converted into arsenic acid, and combines withthe disengaged potash of the nitrate, forming a superarseniateof potash: this remains in the retort in the form of a whitesaline mass, and is afterwards dissolved and crystallized. Thenitrous acid is not worth condensing, as the process is notlikely to be performed on a great scale.

Qualities. — Arseniate, or rather superarseniate % of potashcrystallizes in beautiful, transparent, tetraedral prisms, havingan excess of acid. They are soluble in water; and the solu-tion reddens the vegetable blues.

Medical properties and uses. — This salt may be used exactlyin the same manner, and in the same cases as the white oxide.It was discovered by Macquer, and long known under thename of " the arsenical neutral salt of Macquer." The doseis from one-sixteenth to one-eighth of a grain, formed into a pillwith crumb of bread.

• The arseniate is uncrystallizable and deliquescent, and altogether a different salt;the Dublin College therefore has improperly named it Arscmas Au.'i.