MERCURY PROCESSING

preparation of the ore for use in various products. Mercury (Hg) has a unique combination of physical properties. Its low melting point (-38.87 C ) and boiling point (356.9 C ), high specific gravity (13.5 grams per cubic centimetre), uniform volume expansion over the entire range of temperatures in its liquid state, and high surface tension (so that it does not wet glass) make it useful for the measurement of temperature in thermometers and of pressure in barometers and manometers. In addition, the high electrical conductivity of liquid mercury has led to its use in sealed electric switches and relays, industrial power rectifiers, fluorescent and mercury-vapour lamps, mercury cell batteries, and as moving cathodes in the large-scale production of chlorine and caustic soda. Because mercury is highly toxic, care must be exercised in its handling and transport. By limiting exposure to mercury metal, vapours, and compounds through such preventive measures as proper ventilation, plant cleanliness and personal hygiene, industrial plants can be made relatively safe from the dangers of mercury poisoning. Additional reading Comprehensive and up-to-date information on many aspects of metallurgy, individual metals, and alloys can be found in convenient reference-form arrangement in the following works: Metals Handbook, 9th ed., 17 vol. (197889), a massive and detailed source prepared under the direction of the American Society for Metals, with a 10th edition that began publication in 1990; Herman F. Mark et al. (eds.), Encyclopedia of Chemical Technology, 3rd ed., 31 vol. (197884), formerly known as Kirk-Othmer Encyclopedia of Chemical Technology, with a 4th edition begun in 1991; and its European counterpart, the first English-language edition of a monumental German work, Ullmann's Encyclopedia of Industrial Chemistry, 5th, completely rev. ed., edited by Wolfgang Gerhartz et al. (1985 ). The Editors of the Encyclopdia BritannicaLeonard J. Goldwater, Mercury: A History of Quicksilver (1972), reviews the early occurrences, recovery, uses, and toxicology of mercury. A collection of conference papers on the properties of mercury is presented in Morton W. Miller and Thomas W. Clarkson (eds.), Mercury, Mercurials, and Mercaptans (1973). John E. Shelton