part in. Metallic Preparations. — Mercury. 675

bath, the sand not rising higher round the vessel than themercury stands within it. By maintaining a steady heat, aconstant circulation of the mercurial vapour is kept up in theupper part of the matrass, and as it combines with oxygen, adull Him first forms on the surface of the mercury, which isnext converted into a black powder, and then into red shiningscales. A part of the mercury is always lost; and as the pro-cess requires much attention, and so long a time for its com-pletion, the preparation is necessarily expensive.

Qualities. — Red oxide of mercury is obtained in the form ofminute, crystalline, very brilliant, sparkling, deep red scales,inodorous, but acrid and caustic, although less so than theformer preparation. It is soluble in several of the acids with-out decomposition. It is soluble in water also, and the solutionchanges to green the syrup of violets. When rubbed withrunning mercury, both are changed into black oxide; andwhen heated to ignition in a glass retort, it is decomposed ;very pure oxygen being obtained, and the metal again returnsto the state of running mercury. According to Lavoisier,100 parts of this oxide contain 7 of oxygen; Fourcroy makesthe proportion of oxygen 8; and Chenevix, IS parts. Thelight partially decomposes the red oxide, hence it should bekept in opaque bottles.

Medical prope/iies a?id uses. — This is a very active prepa-ration of mercury, and has been employed by some very cele-brated practitioners * as an internal remedy in syphilis. It is,however, very apt to occasion vomiting, purging, and otherwiseviolently to affect the stomach and bowels ; consequently it isnow scarcely ever exhibited internally, or employed as an anti-syphilitic. The dose may be gr. j. combined with gr. ss. ofopium, in the form of pill, night and morning. It is chieflyused as an external stimulant and escharotic, in the same casesas the nitric oxide ; being previously rubbed to a fine powder,and either sprinkled over the ulcers; or united with lard, andapplied as an ointment.

HYDRAItGYItl OXYMURIAS, Lond. Oxymuriate ofMercury.

" Take of purified mercury, two pounds; sulphuric acid,thirty ounces (by weight); dried muriate of soda, four pounds.Boil the mercury with the sulphuric acid in a glass vessel, untilthe sulphate of mercury becomes dry: rub this, when it is cold,with the muriate of soda in an earthen-ware mortar; thensublime it in a glass cucurbit with a gradually raised heat."

Murias Hydraugyri corrosivus, Edin. Corrosive Mu-riate of Mercury.

1 John Hunter.XX 2