Mercuric Bromide. HgBr2. Syn. Protobromide of mercury, Hydrargyri bibromidum. Prep. Two equal parts of bromine and mercury and sublime. Soluble reddish mass; resembles the iodide in its action.—Dose, 1⁄20 to 1⁄8 gr.
Mercuric Chloride. HgCl2. Syn. Protochloride of mercury, Perchloride of mercury, Bichloride of mercury, Corrosive sublimate; Hydrargyri perchloridum (B. P.), Hydrargyri bichloridum (Ph. L.), Sublimatus corrosivus (Ph. E.), Sublimatum corrosivum (Ph. D.), Hydrargyri chloridum corrosivum (Ph. U. S.), Hydrargyri murias corrosivus, L. This is the ‘corrosive sublimate’ of the shops.
Prep. 1. (Ph. L.) Mercury, 2 lbs.; sulphuric acid, 211⁄2 fl. oz.; boil to dryness, and rub the residuum, when cold, with sodium chloride, 11⁄2 lb., in an earthenware mortar; lastly, sublime by a gradually increased heat.
2. (Ph. E.) Mercury, 4 oz.; sulphuric acid, 2 fl. oz. 3 fl. dr.; pure nitric acid, 1⁄2 fl. oz.; dissolve, add of sodium chloride, 3 oz., and sublime as before.
3. (Ph. D.) ‘Persulphate of mercury’ (mercuric sulphate), 2 parts; dried sodium chloride, 1 part; triturate, &c., as before.
4. (Ph. B.) Reduce sulphate of mercury, 20 oz., and chloride of sodium, dried, 16 oz., each to fine powder, and having mixed them add black oxide of manganese, in fine powder, 1 oz., thoroughly by trituration in a mortar, place the mixture in an apparatus adapted for sublimation, and apply sufficient heat to cause vapours of perchloride of mercury to rise into the less heated part of the apparatus arranged for their condensation.
Obs. In preparing corrosive sublimate, as well as calomel, by the common process, the solution of the mercury is usually made in an iron pot, set in a furnace under a chimney, to carry off the fumes; and the sublimation is conducted in an earthen alembic placed in a sand bath, or in an iron pot, covered with a semi-spherical earthen head. Corrosive sublimate
may also be made by the direct solution of mercuric oxide in hydrochloric acid, or by bringing its constituents together in the state of vapour. The latter plan was patented by the late Dr A. T. Thomson.
Prop. The mercuric chloride of commerce occurs in white, semi-transparent, crystalline masses, of considerable density; it possesses an intense coppery taste, is soluble in about 16 parts of cold, and in 3 parts of boiling water; the boiling solution deposits its excess of salt in long white prisms as it cools; soluble in alcohol and ether, in the latter so much so that it has even the property of withdrawing it from its aqueous solutions; the addition of hydrochloric acid, ammonious chloride or camphor, increases its solubility in all these menstrua. It is decomposed by contact with nearly all metallic bodies, and in solution by various organic substances, and by exposure to light. Sp. gr. 5·2 (5·14 to 5·42—Liebig). It melts at about 509° Fahr., and boils and volatilises at a higher temperature.
Tests. The presence of mercuric chloride may, under most circumstances, be readily detected by the tests given. To distinguish it from other salts, special tests for chlorine or hydrochloric acid must be applied. If on filtering the solution, acidulating it with dilute nitric acid, and testing it with silver nitrate, a cloudy white precipitate be formed, which is insoluble in excess of the precipitant, and in nitric acid, but soluble in ammonia water, and blackened by lengthened exposure to light, corrosive sublimate is shown to be present in the substance examined. Calomel, the only compound of mercury with chlorine besides corrosive sublimate, is an insoluble powder, which could not, therefore, be found in the filtered liquid. Calomel, or the white precipitate formed by the mercurous salt, with hydrochloric acid and the soluble chlorides, is soluble in excess of the precipitant, and is not only insoluble in liquor of ammonia, but is immediately blackened by it.