Mercuric Sulphide is the principal ore of mercury occurring in nature as the mineral cinnabar (q.v.), and is extensively used as a pigment, vermilion (q.v.). It is obtained as a black powder by triturating mercury with sulphur, the compound thus formed being known in pharmacy as Aethiops mineralis, and also by pre cipitating a mercuric salt with sulphuretted hydrogen. There are three crystalline forms of mercuric sulphide :—the light red form aHgS corresponding with cinnabar or vermilion ; the black cubic variety a'HgS corresponding with metacinnabarite; a deep red hexagonal form j3 HgS not occurring in nature. Mercuric sulphide is only slightly acted upon by nitric acid ; it dissolves in aqua regia ; chlorine gives a yellow compound, and it dissolves in potassium sulphide solutions to form double sulphides.
Mercurous Sulphate, is a white, sparingly soluble, crys talline substance obtained by adding sodium sulphate to a solu tion of mercurous nitrate. Mercuric sulphate, is a white, soluble salt obtained by dissolving mercury in hot strong sulphuric acid; on digestion with water, it decomposes into an insoluble basic salt, known as turbith or turpeth mineral, and into a soluble acid salt, Mercury Phosphide, is obtained as brilliant red, hexa gonal crystals by heating mercury with phosphorus iodide to 300° and removing the mercuric iodide simultaneously formed by means of potassium iodide solution. Mercurous phosphate, and mercuric phosphate, are obtained as white precipitates by adding sodium phosphate to solutions of mercurous and mercuric nitrates respectively.
Mercurammonium Compounds.—With ammonia and ammon ium salts, mercury compounds yield a number of substances, many of which have long been used in medicine. By the action of dry ammonia on calomel mercuroso-ammonium chloride, is obtained ; aqueous ammonia on calomel gives di mercuroso-ammonium chloride, By adding ammonia to a solution of mercuric chloride, mercurammonium chloride, known in pharmacy as "infusible white precipitate," is obtained ; "fusible white precipitate" is mercuro-diammonium chloride, and is obtained by adding a solution of mercuric chloride to hot solutions of ammonium chloride and ammonia so long as the precipitate first formed redissolves; the substance separates out on cooling. With ammonia and a strongly
alkaline solution of mercuric iodide in potassium iodide (Nessler's solution) there is obtained a yellow precipitate of HO•Hg•NH•HgI; this reaction is the most delicate test for ammonia, a yellow color ation being given by minute traces. By passing dry ammonia over precipitated mercuric oxide at 130°, a nitride, N2Hg3, is ob tained. The oxide and ammonia solution gives the stable and basic mercurhydroxylamine, Analysis.—Mercury compounds, when heated in a closed tube with sodium carbonate, yield a grey to black sublimate of metallic mercury, which readily unites to form visible globules. The metal is precipitated from solutions on to bright copper-foil; the mer cury coating becomes silvery on rubbing and disappears when the quicksilvered copper is heated in a sublimation tube.
Solutions of mercurous salts with hydrochloric acid give a white precipitate of calomel, which becomes jet-black on treatment with ammonia. Stannous chloride, in its twofold capacity as a chloride and a reducing agent, precipitates both mercurous and mercuric solutions, at first as calomel, and on addition of an excess of reagent the precipitate becomes grey through conversion into finely-divided quicksilver. Sulphuretted hydrogen, when added very gradually to an acid mercuric solution, gives at first an almost white precipitate, which, on addition of more and more reagent, assumes successively a yellow, orange and at last jet black colour. The black precipitate is HgS, identified by its great heaviness, and insolubility in boiling nitric or hydrochloric acid. Aqua regia (q.v.) dissolves it as chloride.
"Mercurous" mercury is quantitatively estimated by precipi tating as calomel and weighing the precipitate on a tared filter at 00°. The metal may also be estimated by distillation in a closed tube with lime, the metal being collected and weighed, or by precipitation as sulphide with excess of sulphuretted hydrogen, the precipitate being collected on a tared filter or Gooch crucible, washed with carbon disulphide, dried and weighed.