The salts of mercury are divided into two classes—mercurous, where mercury is a monad element, and unites with one atom of chlorine; and mercuric salts, where it plays the part of a dyad element, or unites with two atoms. The latter of these will be taken first.
Mercury, Pure. (Ph. B.) Syn. Hydrargyrum purum. Place commercial mercury, 3 lbs., in a glass retort or iron bottle, and applying heat cause 21⁄2 lbs. of the metal to distil over into a flask employed as a receiver. Boil on this for five minutes hydrochloric acid, 3 dr., diluted with distilled water, 9 fl. dr., and having by repeated affusions of distilled water, and decantations, removed every trace of acid, let the mercury be transferred to a porcelain capsule, and dried first by filtering paper, and finally on a water bath.
Mercuric Salts. Tests. Sulphuretted hydrogen and ammonium sulphide, added in very small quantities, produce on agitation a perfectly white precipitate, which acquires successively a yellow, orange, and brownish-red colour, as more of the test is added; and, ultimately, when the test is added in considerable excess, an intensely black colour. This precipitate is insoluble in excess of the precipitant, potassium hydrate, potassium cyanide, hydrochloric acid, or nitric acid, even when boiling; but it dissolves readily and completely in potassium sulphide and in ‘aqua regia’ with decomposition. These reactions are characteristic.
Ammonia gives a white precipitate.
Potassium hydrate gives a reddish precipitate, turning yellow when the test is added in excess. The presence of ammonia causes the precipitate to be white, and when the solution
contains much acid both reactions are imperfect.
Alkaline carbonates give a brick-red precipitate.
Potassium iodide gives a scarlet precipitate, which is soluble in excess, and in alcohol, and solution of sodium chloride.
The alkaline bicarbonates either do not disturb the solution, or only cause a slight degree of opalescence.
Mercuric Acetate. Hg(C2H3O2)2. Syn. Protacetate of mercury. Prep. By dissolving mercuric oxide in warm acetic acid. It crystallises in brilliant micaceous lamina, soluble in their own weight of cold water, and somewhat more soluble in boiling water. According to Robiquet, this is the basis of Keyser’s antivenereal pills, which do not contain subacetate of mercury, as has been asserted.