LEAD PROCESSING

preparation of the ore for use in various products. Lead (Pb) is one of the oldest metals known, being one of seven metals used in the ancient world (the others are gold, silver, copper, iron, tin, and mercury). Its low melting point of 327 C (621 F), coupled with its easy castability and softness and malleability, make lead and lead alloys especially suitable for a wide range of cast products, including battery grids and terminals, counterweights, plumbing components, and type metal. With a specific gravity of about 11.35 grams per cubic centimetre, lead is the densest of the common metals, except for gold; this makes it a good shield against X rays and gamma radiation. Its combination of density and softness make it an excellent barrier to sound. Compared with other metals, lead is a poor conductor of heat and electricity, although it has excellent corrosion resistance when it can form an insoluble protective coating on its surface. The metal has a face-centred cubic crystal lattice structure. Approximately 30 percent of all lead consumed is in the form of lead compounds, such as oxides, tetraethyl and tetramethyllead, lead chromates, sulfates, silicates, and carbonates, and organic compounds. These lead compounds have been used in paste mixtures in storage batteries, in cements, glasses, and ceramics, as pigments in paints, and as an antiknock agent in gasoline. 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 Britannica A broad review of lead history, mining, and production, with emphasis on uses, is presented in Lead Industries Association, Lead in Modern Industry: Manufacture, Applications, and Properties of Lead, Lead Alloys, and Lead Compounds (1952). Wilhelm Hofmann, Lead and Lead Alloys: Properties and Technology (1970; originally published in German, 2nd ed., 1962), is a comprehensive technical review. John S. Nordyke (ed.), Lead in the World of Ceramics: Source Book for Scientists, Engineers, and Students (1984), examines the properties and uses of lead compounds in one specific area. Michael L. Jaeck (ed.), Primary and Secondary Lead Processing (1989), presents papers of an international symposium on the subject. Thomas S. Mackey and R. David Prengaman (eds.), Lead-Zinc '90: Proceedings of a World Symposium on Metallurgy and Environmental Control (1990), is another collection, containing many papers on state-of-the-art technology for extracting and purifying lead, zinc, and some other metals. Frank E. Goodwin Adolph L. Ponikvar