SILVER PROCESSING

preparation of the ore for use in various products. Silver has long been valued for its white metallic lustre, its ability to be readily worked, and its resistance to the corrosive effects of moisture and oxygen. The lustre of the pure metal is due to its electron configuration, which results in its reflecting all electromagnetic radiation of wavelengths shorter than 3000 angstroms. Since 3000 angstroms is in the ultraviolet range, all visible light is effectively reflected, thus conferring the white colour. Silver (Ag), like gold, crystallizes in the face-centred cubic system. It melts when heated to 962 C (1,764 F). With a density of 10.49 grams per cubic centimetre, it is the lightest of the precious metals. It is also the least noble of the precious metals, reacting readily with many common reagents such as nitric acid and sulfuric acid. Metallic silver can be dissolved from gold alloys of less than 30 percent gold by boiling with 30-percent-strength nitric acid in a process referred to as parting. Boiling with concentrated sulfuric acid to separate silver and gold is called affination. Both these processes are used on a commercial scale for separating silver and gold. James Edward Hoffmann 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 on the precious metals. 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. F.W. McQuiston, Jr., and R.S. Shoemaker, Gold and Silver Cyanidation Plant Practice, 2 vol. (197581), provides a wealth of information for the commercial operator, including actual flowsheets and operating data from a variety of gold and silver operations around the world. James Edward Hoffmann