Mercury Tungstates

Normal mercurous tungstate, Hg₂WO₄, is formed, on adding a soluble mercurous salt to a solution of alkali tungstate, as a yellow precipitate, which darkens in colour when dried and leaves tungstic anhydride when ignited. Owing to its insolubility in water, this salt affords a means for the separation and estimation of tungstic acid. An acid mercurous salt, 2Hg₂O.3WO₃.8H₂O, is described by Lefort, but its existence is doubtful.

Normal mercuric tungstate, HgWO₄, is obtained as a light yellow precipitate on adding the acetate to a saturated solution of sodium tungstate. A basic salt, 3HgO.2WO₃, is obtained as a heavy white precipitate when a boiling solution of mercuric chloride is treated with an insufficient quantity of alkali tungstate. An acid salt, 2HgO.3WO₃, is formed as a white precipitate on mixing neutral solutions of mercuric nitrate and an alkali tungstate. Both these salts are insoluble in water, are decomposed by boiling alkalies with separation of mercuric oxide, and on ignition yield tungstic anhydride.

The following salts have been described: HgO.3WO₃.7H₂O, HgO.5WO₃.5H₂O, and 3HgO.5WO₃.5H₂O.