Mercury is a metal distinguished from all others by its extreme fusibility, which is such that it does not take the solid state until it is cooled to the 39o below 0 in Fahrenheit's thermometer, and is therefore always fluid in the temperate climates of the earth. From this circumstance, and its resemblance to silver in colour and metallic splendour, it has been usually denominated quick-stiver. The term mercury, although almost universally employed by chemical authors, is strongly objected to by Mr. Gray, the author of The Operative Chemist, who complains that "medical authors and chemists of the medical professions, still continue to call this metal (which he denominates quick) mercury, that name having been formerly used by the priest-physicians and priest-chemists, to mystify and hoax their patients and the public. It were to be wished that now chemistry and medicine are almost exclusively in the hands of the laity, they would abstain from this ridiculous mummery." The same author also informs us that there are two kinds of quicksilver in the market, - Spanish and Austrian, both of which are very pure; and that " the source of the impure quicksilver in the apothecaries' shops, is the purchase of the quick from the silvering tables of bankrupt or deceased looking-glass makers, which is of course impregnated with tin, and sometimes lead and bismuth; this quicksilver is cheaper than the pure, and is thought by them good enough for making blue pill and blue ointment." Mr. Gray does not, however, censure this pernicious practice of the laity, notwithstanding he is so indignant at the presumed alteration of a mere term of doubtful propriety by our learned forefathers.

The specific gravity of mercury is at 212° Fahr. 13.375; at 160°, 13.580, and at 40° below zero it increases to 15. 632, when it is a malleable solid body. It is volatile, and rises in small portions at the common temperatures of the atmosphere, as is evinced by several experiments, more especially in a vacuum, such as obtains in the upper part of a barometer tube. At the temperature of 650° it boils rapidly, and rises copiously in fumes: it has been attempted to employ the mechanical force which it then exerts as a motive power similar to that of the steam engine; but the loss of the metal, by the extreme subtlety of the vapour passing apparently impervious joints, occasioned, we are informed, its abandonment. Mercury is sometimes found native, but generally combined with sulphur, when it is denominated cinnabar; it is separated from the sulphur by distillation with quicklime or iron filings. Owing to the property which mercury possesses of dissolving completely some of the baser metals, it is extremely liable to adulteration; and the union of the metals is so strong, that they even rise with the quicksilver when distilled.

The impurity of mercury is generally indicated by its dull aspect; by its tarnishing and becoming covered with a coat of oxide on long exposure to the air; by its adhesion to the surface of glass; and when shaken with water in a bottle, by the speedy formation of a black powder. Lead and tin are frequent impurities, and the mercury becomes capable of taking up more of these if zinc or bismuth be previously added. In order to discover lead, the mercury may be agitated with a little water, in order to oxidize that metal; pour off the water and digest the mercury with a little acetic acid: this will dissolve the oxide of lead, which will be indicated by a blackish precipitate with sulphuretted water; or to this acetic solution, add a little sulphate of soda, which will precipitate a sulphate of lead, containing, .when dry, 72 per cent. of metal. If only a very minute quantity of lead be present in a large quantity of mercury, it may be detected by solution in nitric acid, and the addition of sulphuretted water. A dark brown precipitate will ensue, and will subside, if allowed to stand a few days; one part of lead may thus be separated from 15,263 parts of mercury.

Bismuth is detected by pouring a nitric solution, prepared without heat, into distilled water; a white precipitate will appear if this metal be present. Tin is manifested in like manner by a weak solution of nitro-muriate of gold, which throws down a purple sediment; and zinc, by exposing the metal to heat. When the metallic mixtures contain a sufficient quantity of mercury to render them soft at a mean temperature, they are called amalgams. Although it is obvious, from the known inferior specific gravity of iron, lead, and silver, that pieces of these metals will float in mercury, like wood in water, it nevertheless forms a very interesting phenomenon. Mercury is readily soluble in acids, as may easily be ascertained; and from its very extensive use in medicine, there are very numerous preparations of it, by which it may be exhibited in powders, pills, or drops. The most usual is calomel, which is a preparation of mercury and muriatic acid, or chlorine, and is hence called, according to the modern nomenclature, proto-chloride of mercury. The deuto-chloride, or corrosive sublimate, is another combination of mercury and chlorine, and forms one of the most powerful and useful, but dangerous medicines, man has ever discovered. Mercury will readily unite with sulphur.

Melt some sulphur in a crucible on the fire, then add a little mercury, and stir the whole well together, and a sulphuret of mercury, or cinnabar, will be formed. That beautiful scarlet pigment called vermilion (see the separate article) is also prepared from mercury and sulphur, and is called by chemists the red sulphuretted oxide of mercury. The property of mercury dissolving a certain portion of gold and silver, enabled alchymists to impose upon mankind, and make it appear as if they had succeeded, in a small degree, in discovering the secret of turning metals into gold and silver. In their operations they employed mercury in which small portions of these metals had been dissolved; and as the mercury was evaporated by great heat, and left the gold and silver behind, the bye-standers were made to believe that these metals had actually been produced in operation by the skill of the experimentalist. Looking-glasses and mirrors are covered on the back with an amalgam of tin, and the glasses are afterwards loaded with weights, to press out gradually the superfluous mercury, which thus exudes from the amalgam. Amongst the numerous uses of this valuable metal, the application of it in the construction of barometers and thermometers is not the least important.

See those inventions.