Bismuth, a metallic chemical element. It is brittle, has a high luster, and is grayish-white with a red or pink tinge. Bismuth is relatively inactive chemically at normal temperatures, but when heated in air it will burn. It is soluble in strong acids such as aqua regia and nitric acid. Bismuth combines directly with fluorine and the other halogen elements, as well as with sulfur and selenium.

Bismuth has some unusual physical properties. It is one of only two elements (gallium is the other) that expand upon solidifying. Except for mercury, bismuth is the poorest heat conductor of all the metals. Bismuth's electrical resistance increases in a magnetic field. This property is greater in bismuth than in any other metal.

Bismuth is used chiefly to make low-melting-point alloys known as fusible alloys, many of which melt at temperatures below 212 F. (100 C.). These alloys are used in electrical fuses and water-heater safety valves, and also in fire detectors and automatic sprinkler systems. Bismuth is sometimes added to alloys of iron, steel, and aluminum to improve the machining qualities of these alloys. Other uses of bismuth are in drugs, cosmetics, glass, and ceramics.

Bismuth occurs in nature as a free metal, but is more common in ores that contain other elements. The principal ores are bismite (Bi2O3) and bismuthinite (Bi2S3). Most bismuth is recovered as a by-product from the mining of lead, copper, tin, and zinc. The leading producers of bismuth are China, Mexico, Peru, Australia, and Japan.

Bismuth in impure form was known to the alchemists of the Middle Ages, but it was usually thought to be a form of tin or lead. It was first identified as a separate element in 1753 by Claude Franois Geoffroy, a French chemist.

Symbol: Bi. Atomic number: 83. Atomic weight: 208.9804. Specific gravity: 9.8. Melting point: 520.34 F. (271.3 C.). Boiling point: 2,840 F. (1,560 C.). Bismuth belongs to Group VA of the Periodic Table and may have a valence of +3 or +5. Several radioactive isotopes of bismuth are known. Only one isotope, Bi-209, is stable.