PLATINUM GROUP

six metals, in order of increasing atomic weight, ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). The elements all possess a silvery white colourexcept osmium, which is bluish white. The chemical behaviour of these metals is paradoxical in that they are highly resistant to attack by most chemical reagents yet, employed as catalysts, readily accelerate or control the rate of many oxidation, reduction, and hydrogenation reactions. Ruthenium and osmium crystallize in the hexagonal close-packed system, and the others have face-centred cubic structures. This is reflected in the greater hardness of ruthenium and osmium. 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 Relevant volumes of Joseph William Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, 16 vol. (192237, reprinted 196065), are an excellent source of descriptive chemistry and historical information. Information on the chemistry of the precious metals is scattered throughout the monumental Gmelins Handbuch der anorganischen chemie, 8th ed. (1924 ), with articles in German and English; since 1981 most of the articles have appeared in English, and the volumes now have English titles: Gmelin Handbook of Inorganic Chemistry (198189) and Gmelin Handbook of Inorganic and Organometallic Chemistry (1990 ). Linda S. Benner et al. (eds.), Precious Metals Science and Technology, trans. from Japanese (1991), is a comprehensive reference. F.E. Beamish, J.C. Van Loon, and Clyde L. Lewis, Analysis of Noble Metals: Overview and Selected Methods (1977); and F.E. Beamish, The Analytical Chemistry of the Noble Metals (1966), are useful texts for information on specific methods for the analysis of precious metals as found in a variety of rock matrices. Despite their ages, Ernest A. Smith, The Sampling and Assay of the Precious Metals, 2nd ed., rev. (1947, reprinted 1987); and Edward E. Bugbee, A Textbook of Fire Assaying, 3rd ed. (1940, reissued 1981), are an excellent place to begin the study and practice of fire assaying, which has changed very little since its beginning in antiquity. Louis J. Cabri (ed.), Platinum-Group Elements: Mineralogy, Geology, Recovery (1981), contains a useful review of the platinum metals chemistry, geology, and analytical chemistry. James Edward Hoffmann