OXIDE OF MERCUHY.
459
Hydrar'gyri Ox'ydum. — Ox'ide of Mer'cury.
History. —The mode of preparing this compound was taught byMoscat in 1797. This oxide is sometimes termed the protoxide, sub-oxide, ash, grey, or black oxide (hydrargyri oxydurn cinereum, hydrargyrioxiduni nigrum ).
Preparation. —In the London Pharmacopoeia it is prepared byadding one ounce of calomel to a gallon of lime water: then frequentlyshake them, set by, and when the oxide has subsided, pour off the super-natant liquor, and wash the precipitate with distilled water: afterwardsdry it (wrapped in bibulous paper) in the air.
In this process double decomposition takes place: chloride of calciumis formed in solution, while oxide of mercury precipitates.
REAGENTS.
1 eq. Chlorine1 eq. Mercury1 eq. Calcium.1 eq. Oxygen .
RESULTS.
. 56
202 ——
20-
8-
— 1 eq. Oxide of Mercury .
. 210
In the Edinburgh Pharmacopoeia one-fourth more lime-water is em-ployed, and the mixture boiled for a quarter of an hour. In the DublinPharmacopoeia, one part of calomel and four of water of caustic potashare employed. In this case chloride of potassium is formed in solution.
Properties. —Pure oxide of mercury is black, or nearly so. The pre-sent preparation, however, is frequently greyish, owing to the presenceof some undecomposed calomel. It is readily decomposed by light(especially by the solar rays), becomes olive coloured, and is resolved intometallic mercury and the binoxide. It is odourless, tasteless, insoluble inwater and the alkalies, but soluble in nitric acid and acetic acid. By theaction of hydrochloric acid it forms water and calomel. When heated itis first decomposed, and then completely dissipated.
Characteristics. —Heated in a glass tube it evolves oxygen, whilemetallic globules are sublimed. Dissolved in nitric acid it forms a proto-mercurial salt, known by the before-mentioned characters for these sub-stances.
Composition. —The composition of this oxide is as follows:—
Eq. Eq.Wt. Per Cent. Sefstrom.
Mercury. 1 ..... 202 ..... 96*19 96*2
Oxygen. 1 . 8 3*81 3*8
Oxide of Mercury. . 1 . 210 .... 100*00 . 100*0
Purity. —Digested, for a short time, in dilute hydrochloric acid, thesolution, when filtered, should form no precipitate with either potash oroxalate of ammonia. If any binoxide had been dissolved, the potashwould throw it down as a reddish or yellowish hydrate. If any carbonateof lime had been precipitated, die oxalate would recognise it.
Physiological Effects. —Pure oxide of mercury is one of the leastirritating of the mercurial preparations, and, therefore, when swallowed,does not produce much disorder of the alimentary canal. In small dosesit acts as an alterative and purgative. When taken in repeated doses,its constitutional effects are similar to those of other mercurials.
Uses. —Mr. Abemethy employed it as a fumigating agent. The fol-lowing arc his directions for using it:—Place the patient in a vapour