Hydrargyri Binoxydum. Lond.1 Binoxide of Mercury

"Take of bichloride of mercury,four ounces; solution of potassa, twenty-eight fluid ounces; distilled water, six pints. Dissolve the bichloride in the water, strain, and add the solution of potassa. Wash the powder thrown down in distilled water, until nothing alkaline be perceived, and dry it with a gentle heat."

Hydrargyri Oxydum rubrum, Dub. Oxide of Mercury.

"Take of purified mercury, any quantity. Put it into an open glass vessel with a narrow mouth and a broader bottom, and expose it to a heat of about 600°, until it be converted into red scales."

Syn. Oxide de Mercure rouge par le feu (F.), Rothes Quecksilberoxyd (G.), Perossido rosso di Mercurio (I.).

In the London process both the bichloride and the potassa are decomposed, a chloride of potassium is formed, which remains in solution whilst the oxide is precipitated in the form of a hydrate.

In the Dublin process the mercury is brought nearly to the boiling point2, so as to be volatilised, in which state it decomposes atmospherical air, attracting its oxygen, and is converted into a red oxide. A small quantity of mercury requires several weeks to be thus oxidised; and, therefore, as much only is introduced into the vessel as can cover its bottom; and both on this account, and in order to prevent the dissipation of the volatilised metal, the shape of the vessel is of some importance. It should have a wide bottom, a long neck, and the extremity extended almost to a point; and it should be heated in a sand bath, the sand not rising higher round the vessel than the mercury stands within it. By maintaining a steady heat sufficient to produce gentle ebullition, a constant circulation of the mercurial vapour takes place in the upper part of the matrass, and as it combines with oxygen, a dull film first forms on the surface of the mercury, which is next converted into a black powder, and lastly into deep red shining scales.

A part of the mercury is always lost; and as the process requires so long a time for its completion, the preparation is necessarily expensive.

1 Hydrargyrus calcinatus, P. L. 1787. Hydrargyri Oxydura Rubrum, P. L. 1824.

2 Irvine makes the boiling point of mercury to be 672°; Crichton 655°; and Dalton, 660°.

Qualities. -Binoxide of mercury, by the London process, is obtained in the form of a deep orange yellow powder; but by the Dublin it is in minute, crystalline, very brilliant, sparkling, deep red scales, inodorous, but acrid and caustic. Each is a binoxide, soluble in a small degree in water, forming a solution which greens the infusion of violets : it is also soluble in several of the acids without decomposition. Potassa and soda decompose these solutions, and precipitate the binoxide of an orange colour. Ammonia forms a white precipitate, which is a triple compound of the acid, the binoxide, and ammonia. When rubbed with running mercury, both are changed into black oxide; and when heated to ignition in a glass retort it is decomposed, very pure oxygen being obtained, whilst the metal returns to the state of running mercury. According to Lavoisier, 100 parts of this oxide contain 7 of oxygen: Mr. Phillips makes the proportion 7.3; Fourcroy, 8: and Chenevix, 15 parts. In equivalents it consists of 1 eq. of mercury=202 + 2 eq. of oxygen = 16; making the equivalent 218 (Hg). The light partially decomposes the binoxide hence it should be kept in opaque bottles.

Medical properties and uses.-This is a very active preparation of mercury, and has been employed by some very celebrated practitionersl as an internal remedy in syphilis. It is, however, very apt to cause vomiting, purging, and otherwise violently to affect the stomach and bowels; consequently it is now scarcely ever exhibited internally, or employed as an antisyphilitic. The dose may be one eighth of a grain to gr. j. combined with gr. ss. of opium, in the form of pill, night and morning. It is chiefly used as an external stimulant and escharotic, in the same cases as the nitric oxide; being previously rubbed to a fine powder, and either sprinkled over the ulcers, or united with lard, and applied as an ointment.