In this country vermilion is commonly made by triturating mercm y with about one sixth of its weight of sulphur, and then subliming. The beauty of the tint is said to depend upon the amount of levigation to which the sublimate is afterwards subjected.
Protosulphide of mercury is also thrown down when sulphuretted hydrogen gas is passed through a solution of a mercuric salt. It is black, but may be made to assume a red colour by sublimation. It is insoluble in aqueous solutions of the alkalies and in all acids except aqua regia. It is dissolved however in hydrochloric acid when arsenic or antimonic acids and some other oxidising agents arc present.
Mercury 4nd iodine form 1. Protolodide of mercury IIgI 2. Scsqui-iodidc of mercury . . . 11g,I, 3. Biniodidc of mercury 1. Protoiodhle of mercury. (He). Green, or diniodide of, mercury. Mercurous iodide. Prepared by triturating an equivalent of mercury with one of iodine, the mixture being moistened with a little alcohol to keep down the temperature and consequently prevent too rapid action and decomposition. It is also precipitated when a mercurous salt is mixed with solution of iodide of potassium. It is somewhat unstable.
2. Scsgui-iodide of mercury (Hg,I,). Mereuroso-mereurio iodide. Pre cipitated when a solution of iodine in iodide of potassium is added to a solution of mercurous nitrate. Alcohol extracts no mercurous iodide from this compound—a proof that it is not a mere mixture of mercu rous and mercuric iodide.
3. Biniodide of mercury (HgI„) Mercuric iodide. Prepaied as the protoiodide, two equivalents of iodine being used, or by precipitation from a mercuric salt by iodide of potassium. It is at first salmon coloured, but by molecular alteration speedily becomes a magnifi cent scarlet. It sublimes in yellow tabular crystals, but on rubbing, scratching, or merely agitating, undergoes the alteration just mentioned and becomes scarlet ; in short, biniodide of mercury is, in crystallo graphic language, dimorphous. During the change beat is evolved.
Double salts of biniodide of mercury with other compounds of mercury and with the alkaline iodides may be easily formed.
Mercury and bromine form compounds very much resembling the iodides.
Mercury and chlorine form two important chlorides : I. Protochloride of mercury . . . . 11gC1 2. Bichlorldc of mercury . . . . . 1. Protochloride of mercury (HgC1). Subeldoride or dichloride of mercury. Mercurous chloride. Calomel. This compound of mercury has been known for nearly three centuries. It was first called calomel (from naAhs,good, and ulAar, black) by Sir Theodore Turquet de Mayenne, though for what reason is not satisfactorily known. It occurs native [MERCURY, in NAT. HIST. DIY.] but for use in medicine is always prepared artificially. This is sometimes accomplished by adding chloride of sodium to a solution of a mercurous salt, and well washing and drying the precipitate. More usually, however, it is obtained by submitting to the action of heat a mixture, in equivalent proportions, of chloride of sodium and protosulpbate of mercury ; double decom position takes place, pmtochloride of mercury sublimes and sulphate of soda remains. If the vessel in which this operation is conducted be small, the calomel condenses in brilliant quadrilateral prisms termi nated by four-sided pyramids; but if the receiver be capacious, and especially if it be filled with steam, the calomel condenses in the form of an exceedingly fine white or slightly buff-tinted powder. By the latter modification of manufacture the trouble of grinding is avoided.
Calomel is tasteless and insoluble in water. The fixed alkalies con vert it into protoxide. Ammonia changes it to black precipitate or mercurous amidochloride (HgC1+ It is very soluble in strong solutions of alkaline salts, but much less so in dilute solutions ; decom position into metallic mercury and mercuric salt accompanies the solution.
2. Bichloride of mercury Perchloride of mercury. Mer curic chloride. Corrosive sublimate. This compound may be formed by the direct union of its constituents, but is usually prepared by submitting to an elevated temperature a mixture, in equivalent pro portions, of bisulphate of mercury and chloride of sodium. The following equation exhibits the reaction :— 140„ 300.