5. MERCURY.
§ 828. Mercury, Hg = 200; specific gravity, 13·596; boiling-point, 350° (662° F.); it becomes solid at -39·4 (-39 F.). This well known and familiar fluid metal evaporates and sublimes to a minute extent at all temperatures above 5°.
When precipitated or deposited in a finely divided state, the metal can be united into a single globule only if it is fairly pure; very slight fatty impurities especially will prevent the union. It is insoluble in hydrochloric acid, soluble to a slight extent in dilute cold sulphuric acid, and completely soluble in concentrated sulphuric and in nitric acids. It combines directly with chlorine, bromine, and iodine, which, in presence of free alkali, readily dissolve it. It is unalterable at 100°, and, when exposed to a high temperature, sublimes unchanged.
Mercurous Chloride (Calomel, HgCl = 235·5; specific gravity, 7·178; subliming temperature, 111·6°; Hg, 84·94 per cent., Cl, 15·06 per cent.), when prepared in the wet way is a heavy white powder, absolutely insoluble in cold, but decomposed by boiling water. It may be converted into the mercuric chloride by chlorine water and aqua regia. Chloride of ammonium, potassium, and sodium, all decompose calomel into metallic mercury and mercuric chloride. It is easily reduced to metal in a tube with soda, potash, or burnt magnesia.
§ 829. Sulphide of Mercury (HgS, Hg, 86·21 per cent., S, 13·79 per cent.) is a black powder, dissolving in nitromuriatic acid, but very insoluble in other acids or in water. It is also insoluble in alkaline sulphides, with the exception of potassic sulphide.
§ 830. Medicinal Preparations of Mercury.—Mercury in the liquid state has been occasionally administered in constipation; its internal use is now (or ought to be) obsolete. Gmelin has found samples contaminated with metallic bismuth—a metal which only slightly diminishes the fluidity of mercury; the impurity may be detected by shaking the mercury in air, and thus oxidising the bismuth. Mercury may also contain various mechanical impurities, which are detected by forcing the metal by means of a vacuum pump through any dense filtering substance. Tin and zinc may be dissolved out by hydrochloric acid, and all fixed impurities (such as lead and bismuth) are at once discovered on subliming the metal.
Mercury and Chalk (Hydrargyrum cum creta).—Mercury, 33·33 per cent.; chalk, 66·67.
Blue Pill (Pilula hydrargyri).—Mercury in a finely divided state, mixed with confection of roses and liquorice root; the mercury should be in the proportion of 33·33 per cent.[902]
[902] The chemical composition of blue pill varies according to its age. Harold Senier has made a careful series of analyses, with the following result (Pharm. Journ., Feb. 5, 1876):—