Hydrargyri Persulphas. Dub. Persulphate of Mercury

"Take of purified mercury, sulphuric acid, of each six parts; nitric acid, one part. Let the mixture be exposed to heat in a glass vessel, gradually increasing the heat, until the matter, when nearly dry, acquire a white colour."

1 John Hunter.

In this process the nitric acid is decomposed, its oxygen combines with the mercury, forming it into a binoxide, which in its turn unites with the sulphuric acid, and forms a persulphate. It is white, in fine crystalline plates, or in prismatic needles; is soluble in 500 parts of cold, and 250 of boiling water. It consists of 1 proportion of binoxide of mercury =216 + 2 proportions of sulphuric acid = 80.2; making the equivalent 296.2 (Hg + 2S). Its chief use is for making the bichloride of mercury.

Officinal preparations. - Hydrargyri Oxydum Sulphuricum, D. Hydrargyri Murias Corrosivum, D. Calomelas sublimatum, D.

Acetas Hydrargyri. Edin. Acetate of Mercury

"Take of purified mercury, three ounces; diluted nitrous acid, four ounces and a half or a little more than may be required for dissolving the mercury; acetate of potassa, three ounces; boiling water, eight pounds. Mix the mercury with the acid; and, towards the cessation of the effervescence, digest, if necessary, until the mercury be completely dissolved. Then dissolve the acetate of potassa in the boiling water; and immediately to this solution, still hot, add the former, and mix them together by agitation. Set the mixture aside to crystallise; then wash the crystals placed in a funnel with cold distilled water; and finally dry them with a very gentle heat.

"In preparing acetate of mercury, it is necessary that all the vessels which are used, and the funnel, be of glass."

Hydrargyri Acetas, Dub. Acetate of Mercury.

"Take of purified mercury, nine parts; diluted nitrous acid, eleven parts; acetate of potassa, nine parts; boiling distilled water, a sufficient quantity. Add the nitric acid to the mercury; and when the effervescence is over, digest, that the metal may be dissolved.

" In the whole of this process glass vessels must be used."

Syn. Acetate de Mercure (F.), Essigsaures Quecksilber (G.), Acetato di Mercurio (I.).

Acetic acid scarcely acts on mercury; but by either of the above processes the acetate may be formed. Nitrate of mercury is first obtained by the action of the nitric acid on the mercury; and this is decomposed by the acetate of potassa, the alkali of which unites with the acid of the metallic salt, and forms nitrate of potassa, which remains in solution; while the disengaged acetic acid combines with the protoxide of mercury, and forms the acetate of mercury, which readily crystallises, and is thus easily separated. By preparing the solution of the nitrate of mercury with a low heat, when there is an excess of acid, the portion of mild acetate of mercury produced is considerable; but if the quantity of acid be sufficient for the saturation only of the oxide, a sudden decomposition of the solution is effected by the hot water which contains the acetate of potassa in solution, independent of the action of the acetate, and a subnitrate of mercury of a yellow colour is precipitated. Hence the propriety of the direction of the Edinburgh College to use more acid "than is required for dissolving the mercury." It is of much importance also that the degree of heat be low; for if a high temperature be employed, the metal is oxidised to a maximum, and the product of the subsequent part of the process is a binacetate, which is very acrid and soluble, instead of the protosalt intended to be produced.

For the success of the process, which often fails, the solution of the acetate of potassa should not be used immediately after it is made, but should be scarcely more than tepid when it is mixed with the solution of the nitrate of mercury; and to the water employed for washing the salt should be added about f 3 j. of distilled vinegar for every Oss. of water; which prevents the partial decomposition of the acetate, and the consequent yellow colour of the crystals, that sometimes occur in the washing.

Qualities. -This salt, when properly prepared, is in small flat crystals of a silvery whiteness, acrid to the taste, soluble in hot water, but scarcely soluble in cold water. It is insoluble in alcohol. The alkalies decompose it, and it is readily decomposed by heat. Light also has this effect, blackening the salt. It consists of 1 eq. of protoxide of mercury = 210 + 1 of acetic acid = 51.48, making the equivalent 261.48.

Medical properties and uses. - Acetate of mercury is anti-syphilitic and alterative; but it is scarcely ever used, unless as the active ingredient of Keyser's pills. As an external application, a solution of it, in the proportion of grs. ij. in f ij. of rose-water, is used in some cutaneous affections. The internal dose is gr. j. night and morning.