BINOXIDE OF MERCURY.

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(, b .) By calcination. —In the Dublin Pharmacopoeia, hydrargyrum oxy-dum rubrum is directed to be prepared by exposing mercury to a heat of600°, in an open glass vessel, with a narrow mouth and broad bottom,until it is converted into red scales. The heat vapourizes the mercury,which in this state attracts oxygen from the air, and forms this red orbinoxide. The long neck of the vessel prevents the escape of the vapoursor newly-formed oxide.

The process is a very tedious one, occupying several weeks ; so thatGeber ’s remark was correct, that “ it is a most difficult and laboriouswork, even with the profoundness of clear-sighted industry.” The appa-ratus which Mr. Boyle contrived for the manufacture of it, was longtermed “ Boyle's Hell,” from a notion that the mercury was tortured in it.

Properties. —When prepared by precipitation it is in the form of anorange-red powder; but when made by calcination, occurs in small bril-liant scales of a ruby red colour. Both varieties agree in the following-properties :—They are odourless, have an acrid metallic taste, are inso-luble in water, but soluble in both nitric and hydrochloric acids. Theyare decomposed and reduced by heat and solar light: the precipitatedvariety is more readily acted on by solar light than the variety made bycalcination.

Characteristics. —When heated in a glass tube by a spi it lamp, itis decomposed into oxygen and mercury: the first may be recognised bya glowing match, the second condenses in small globules. It dissolvescompletely in hydrochloric acid: the solution contains bichloride of mer-cury, which may be known by the tests hereafter to be mentioned for thissubstance ( vide Hydrargyri Bichloridum).

Composition. —The composition of this substance is as follows :—

Eq. Eq.Wt. PerCent. Sefstrom. Donovan.

Mercury . 1 .... 202 . . . 92-66 .... 92 - 68 .... 92 - 75

Oxygen .2 .... 16 . . . 7'34 .... 7'32 .... 7'25

Binoxide of Mercury . 1 .... 218 . . . 100-00 .... 100-00 .... 100-00

Binoxide of mercury prepared by precipitation usually contains somewater.

Purity. —Binoxide of mercury should be completely dissipated byheat, and be insoluble in water. Its solution in nitric acid should be un-affected by nitrate of silver, by which the absence of any chloride isshown. If an insufficient quantity of potash be employed in the prepa-ration of the precipitated variety, the product is brownish or brick-dustcoloured, and contains oxichloride of mercury (composed, according toSouberain, of 1 eq. bichloride of mercury and 3 eqs. of binoxide:Dumas, Traite de Chimie, iii. 615).

Physiological Effects. —Binoxide of mercury is a powerful irritant,and when taken internally, even in small doses, readily excites vomitingand purging; large doses would excite gastro-enteritis. Orfila ( Toxicol.Gen.) found that binoxide, obtained by precipitation from four grains ofbichloride, killed a dog in eighteen minutes. The constitutional effectsof this preparation are the same as those of mercurials generally.

Uses. —Binoxide of mercury is rarely employed as a medicine. Ithas been applied as an escharotic, either in the form of powder or oint-ment. Internally it was formerly exhibited to excite salivation in