Mercury is the only common metal existing as a liquid at ordinary temperatures. The pure metal has a silver-white mirrorlike appearance. Mercury is below cadmium in Group 2 of the periodic table. It is relatively stable in dry air, but in moist air slowly forms a gray oxide coating. Mercury has high surface tension; when spilled, it breaks up into tiny beads which often become lodged in cracks.
Mercury forms numerous compounds, assuming +1 valence in mercurous compounds and +2 valence in mercuric compounds. Mercury is not attacked by dilute hydrochloric or sulfuric acid. It reacts with hot nitric acid to form mercuric nitrate, Hg(No3)2. An excess of mercury reacts with nitric acid to form mercurous nitrate, HgNO3. Mercury reacts with hot concentrated sulfuric acid to form mercuric sulfate, HgSO4; with excess mercury, mercurous sulfate, Hg2SO4, is formed. Mercury reacts directly with the halogens to form mercuric salts. At elevated temperatures mercury reacts slowly with oxygen to form mercuric oxide, HgO. A mercurous oxide may be formed chemically but is unstable, decomposing to a mixture of mercury and mercuric oxide.
Mercury occurs uncombined in nature to a limited extent. The metal is obtained commercially from cinnabar, a mercuric sulfide ore; it is easily separated by roasting the ore in air. The metal is usually purified by repeated vacuum distillation.
Mercury metal has many uses. Because of its high density, it is used in barometers and manometers. Because it has a high rate of thermal expansion that is fairly constant over a wide temperature range, it is used extensively in thermometers. Mercury is important as a liquid contact material for electric switches. It is used in mercury-vapor lamps, which emit light rich in ultraviolet radiation; various kinds of such lamps are used for street lighting, as sun lamps, and in "black lights" (see lighting). Mercury is used as an electrode in the production of chlorine and sodium hydroxide. It is also used in certain electric batteries. With some other metals mercury forms a special type of alloy called an amalgam; a special amalgam (mostly mercury, silver, and tin) is used in dentistry for filling teeth.
Mercury compounds have many uses. Calomel (mercurous chloride, Hg2Cl2) is used as a standard in electrochemical measurements and in medicine as a purgative. Mercuric chloride (corrosive sublimate, HgCl2) is used as an insecticide, in rat poison, and as a disinfectant. Mercuric oxide is used in skin ointments. Mercuric sulfate is used as a catalyst in organic chemistry. Vermilion, a red pigment, is mercuric sulfide; another crystalline form of the sulfide (also used as a pigment) is black. Mercury fulminate, Hg(CNO)2, is used as a detonator. Mercury forms many organic compounds. Mercurochrome (in 2% aqueous solution) is used in medicine as a topical antiseptic. Mercury compounds were formerly used in the treatment of syphilis.
See also mercury poisoning.
Harmful effects of mercury compounds. Manufacture of paints, various household items, and pesticides uses mercury; the finished product and the waste products released into air and water may contain mercury. The aquatic food chain can concentrate organic mercury compounds in fish and seafood, which, if eaten by humans, can affect the central nervous system, impairing muscle, vision, and cerebral function, leading to paralysis and sometimes death (see Minamata disease). Acute mercury poisoning causes severe digestive-tract inflammation. Mercury accumulates in the kidneys, causing uremia and death. Chronic poisoning, from occupational inhalation or skin absorption, causes metallic taste, oral inflammation, blue gum line, extremity pain and tremor, weight loss, and mental changes (depression and withdrawal). Drugs containing mercury can cause sensitivity reactions, sometimes fatal. In young children, acrodynia (pink disease) is probably caused by an organic mercury compound in house paints.
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Metallic chemical element, chemical symbol Hg, atomic number 80. Mercury is the only elemental metal that is liquid at ordinary temperatures, with a freezing point of −38 °F (−39 °C) and a boiling point of 674 °F (356.9 °C). Silvery white, dense, toxic (see mercury poisoning), and a good conductor of electricity, mercury is occasionally found free in nature but usually occurs as the red sulfide ore, cinnabar (HgS). It has many uses—in dental and industrial amalgams, as a catalyst, in electrical and measuring apparatus and instruments (e.g., thermometers), as the cathode in electrolytic cells, in mercury-vapour lamps, and as a coolant and neutron absorber in nuclear power plants. Many of mercury's compounds, in which it has valence 1 or 2, are pigments, pesticides, and medicinals. It is a dangerous pollutant because it concentrates in animal tissues in increasing amounts up the food chain.
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First series of U.S. manned spaceflights (1961–63), which began about three weeks after Yury A. Gagarin became the first human in space. In May 1961 Alan B. Shepard rode the first Mercury space capsule, Freedom 7, on a 15-minute, 302-mi (486-km) suborbital flight, attaining a maximum altitude of 116 mi (186 km). The first U.S. manned flight in orbit was that of the Friendship 7, carrying John H. Glenn, Jr., in February 1962; it completed three orbits. The last Mercury flight, Faith 7, launched in May 1963, was the longest, making 22 orbits in about 34 hours.
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Mercury may also refer to: