MERCURY, or QUICKSILVER, a me.; tallic element which has been known for many centuries and which is distinguished from the other metallic elements by the fact • that it is liquid at ordinary temperatures. Mercury oe curs native in the metallic form, but by far the larger part of it is obtained by' distilling the native sulphide, cinnabar (Hgs), in a current of air which is regulated so as to burn the sul-1 phur of the sulphide, while leaving the mer cury in the metallic state. Cinnabar occurs abundantly at Idria, Austria, at Almaden,. Spain, and at New Almaden, near San Fran cisco Bay, and it is from these sources that the mercury of commerce is chiefly obtained. It occurs as veins and disseminated deposits, the. ores of which are believed to have been intro.; duced by hot waters of magmatic (q.v.) origin.. Spain is the largest producer and the chief out put in the United States comes from Califor nia, though deposits are known in Texas and; Oregon. Mercury freezes at' 37.9° F. below zero and boils, at the ordinary pressure (760 mm.), at 675° F. Its specific gravity at 32° F., when compared with water at 39° F., is 13.596. Its specific heat at ordinary temperatures is about 0.0331, and its average co efficient of expansion between 32° F. and 212° F. is 0.00010085 (Fahrenheit scale). The ratio of the specific heat of the vapor at constant pressure to its specific heat at constant volume' has been found, experimentally, to be 1.666,. which indicates that the molecules of the vapor are monatomic and that they behave, so far as their collisions among themselves are con cerned, as though they were elastic spheres. (See GASES, KINEric THEORY oP). Mercury may be freed from dust and dirt by filtering it through leather. To remove tin, lead and other dissolved metals, the mercury may be left for some weeks in contact with concentrated sul phuric acid and subsequently digested with di lute nitric acid; or it may he several times dis tilled. Various other modes of purification are also known.
The metal is chiefly used, in the arts, for the extraction of gold from crushed ore or fine gravel, the ore being washed by a gentle stream of water over a copper plate which is amalgamated with mercury. The gold particles, being heavy, sink through the water so as to come into contact with the copper plate, where they are held by the mercury in the form of a gold amalgam. (See GoLn and AMALGAM). In physics, mercury is also greatly, used for filling thermometers and barometers, and for many other purposes. It is used in medicine both in the metallic form arid in its compound; with other elements. Metallic mercury, when rubbed up in a mortar with confection of roses until its globules are so fine as to be indistin guishable to the eye, is known as "blue mass" and is administered in the form of pills, as a cholagogue.
Mercury has the chemical symbol • Hg (from "hydrargyrum," its Latin name), and an atomic weight of 200.3 if 0-16, or 198.8 if H = 1. It forms two oxides, each of which give rise to a series of stable salts. .The metal does not oxi dize upon exposure to air at ordinary tempera tures, but when heated nearly to its boiling point in air or in oxygen it slowly oxidizes, with the formation of mercury monoxide (or mercuric oxide), HgO. When prepared in this manner the monoxide is crystalline and red, and for this reason it is familiarly .knqwn as the
"red oxide." The same substance may be pre pared in an allotropic form by precipitating a solution of Mercuric nitrate by the addition of caustie potash, the monoxide then coming down as an amorphous yellow powder. The red oxide turns black when strongly heated, but re covers its color upon cooling. When heated to redness the monoxide decomposes into metallic mercury and free oxygen. It can, therefore, be used as a source of oxygen; and it was in fact by heating this substance that oxygen was first discovered by Priestley. By acting upon the red oxide or upon metallic mercury by excess of nitric acid, mercuric nitrate, Hg(N003, is formed; while if nitric add is allowed to act upon excess of mercury, mercurous nitrate, HgN0A, is obtained. The corresponding sul phates of the metal are obtained by acting upon Metallic mercury with sulphuric acid, mercuric sulphate (HgSO4) or mercurous sulphate (Hg..SO4) being obtained, according to the conditions of the experiment. Mercuric sul phide, HgS, which occurs native as the mineral• cinnabar, and which is also known as vermil ion, is bright red in color and may be prepared artificially by heating mercury with sulphur, or by passing sulphuretted hydrogen gas through a solution of •mercuric salt. When obtained in the latter way it comes down as a ;black amor phous powder, which may be, brought into the normal red crystalline form by sublimation. Mercury forms two chlorides which are exten sively used, especially in medicine. Mercuric chloride (also known as "bichloride of mer cury" or "corrosive sublimate"), HgCI,, is pre pared by heating a mixture of ,equal parts of mercuric sulphate, HgSO., and common salt, NaCI; the reaction being HgS0. HgCI, + Na.,S0.. The bichloride is fairly solu ble in water and dissolves readily in a solution of sal ammoniac. It is also quite soluble in alcohol. It crystallizes in the trimetric system,. melts at 509° F. and boils at 563° F. It is in tensely poisonous and is one of the most power ful germicides known. It is used in surgery. and medicine as an antiseptic and disinfectant, and is occasionally administered internally in very small doses. Mercurous chloride, HgCI more familiarly known as "calomel)) or as the mild chloride"), is a white powder, insoluble in water and is greatly used, in medicine, both as a cholagogue and otherwise. It may be pre pared in various, ways, but the usual method is by heating four parts of corrosive sublimate with three parts of metallic mercury; the mer cury combining with half of the chlorine of the corrosive sublimate, as indicated by the equa tion HgCI, Htv.c2HgCl. The calomel sub limes and must then be ground to a fine powder and thoroughly washed, in order to remove any free soluble corrosive sublimate that may not have been decomposed. The so-called *white precipitate,* which is obtained when ammonia is added to a solution of corrosive sublimate, has the composition NH,HgCI. Mercurous oxide, or *black oxide of mercury,* Hg,O, may be obtained as a black powder by digesting calomel with excess of caustic potash. It decomposes into the red oxide and metallic mercury upon expo sure to light, or upon being heated to the boil ing point of water. Many other compounds of mercury are known, but they of less im portance than the ones here given.