Hydrargyri Oxydum Cinereum

Lond.

Grey Oxide of Mercury.

"Take of chloride of mercury, an ounce; lime-water, a gallon. Mix, and agitate assiduously; set aside, and when the oxide has subsided pour off the fluid; lastly, wash this with distilled water, until nothing alkaline can be perceived, and dry it in the air wrapped in bibulous paper.

1 M. Paysse, Annales de Chimie, li. 202.

2 System of Materia Medica, ii. 329. Dr. Murray suggests that it should have been named Subnitras Hydrargyri ruber, but improperly, as the undecomposed salt which it contains is a nitrate.

3 Trans, of the Pharm. p. 110.

Oxydum Hydrargyri cinereum, Edin. Grey Oxide of Mercury.

"Take of submuriate of mercury, half an ounce; lime-water, Jive pounds. Boil the submuriate in the solution, for a quarter of an hour in a slightly covered vessel. Pour off the supernatant fluid, then wash the oxide with distilled water, and dry it."

Hydrargyri Oxydum nigrum, Dub. Black Oxide of Mercury.

"Take of sublimed calomel, one part; hot solution of caustic potassa, four parts. Rub them together; the oxide acquires a black colour; then wash it well with water, and dry it, in a moderate heat, on bibulous paper."

Syn. Oxide gris de Mercure (F.), Schwarzes gesauertes Quecksilber (G.), Protossido cinereo di Mercurio (I.).

In the London and Edinburgh processes, the lime-water decomposes the calomel, and is itself also decomposed: its calcium unites with the chlorine of the chloride, whilst its oxygen combines with the mercury, and the insoluble protoxide remains of a greyish colour: the chloride of calcium which is formed, being soluble, is easily separated by washing. In the Dublin process, the alkaline solution yields the oxygen required in the same manner as the lime-water in the London process.

Qualities.-Grey oxide of mercury, properly prepared, is in the form of an impalpable, blackish grey-coloured powder, which becomes paler if exposed to air and light. It is inodorous, insipid, and insoluble in water. In the state in which it is usually found in the shops, it is of a light grey colour, almost approaching to a white : when prepared according to the London formula, it has been supposed1 that the product is strictly a chloride of mercury mixed with the protoxide; and I have found, from experiment, that this is actually the case. The constituents of the protoxide are 96*2 parts of mercury, and 3.8 of oxygen, in 100 parts, or one eq. of mercury = 202 + 1 of oxygen = 8; making the equivalent 210 (Hg). It ought to dissolve totally in nitric and acetic acids, and to decompose the hydrochloric, which again changes it into the chloride.

Medical properties and uses. - The grey oxide of mercury, when well prepared, may be used as a substitute for the oxide prepared by trituration; and as it is more likely to be always of an uniform strength, it may of course be more depended on than that preparation. It has been, however, objected to for forming ointment for the purposes of mercurial frictions

1 Murray's System of Materia Medica, ii. 326.

(see Ung. Oxydi Hydrargyi cinerei); but perhaps the objections have originated from that form of the preparation having been used which contains the triple salt. We have seen it used with advantage for fumigation, both locally applied to assist the healing of venereal ulcers, and, generally, to bring the habit under the mercurial influence, when the mercury could not be introduced by the ordinary mode. The dose of this oxide is from gr. i. to grs. iij., given in the form of pill twice a day.

Officinal preparation.- Unguenlum Oxydi Hydrargyri cinerei, E.