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An Encyclopedia of the History of Technology part 8

An Encyclopedia of the History of Technology part 8. This one of a kind encyclopedia presents the entire field of technology from rudimentary agricultural tools to communication satellites in this first of its kind reference source. Following an introduction that discusses basic tools, devices, and mechanisms, the chapters are grouped into five parts that provide detailed information on materials, power and engineering, transportation, communication and calculation, and technology and society, revealing how different technologies have together evolved to produce enormous changes in the course of history | PART ONE MATERIALS relatively pure native metal. The rate of this transformation increased rapidly soon after the establishment of the Tigris and Euphrates civilizations. The wealth and specialized demand provided by these urban societies must have stimulated early copper workers to prospect in the northern mountainous regions where weathered outcrops of copper were most likely to be encountered. The earliest copper workers appear to have extracted their metal from oxide or carbonate ores which although not always rich or plentiful could generally be smelted successfully in the primitive furnaces then available. The early smelters all appeared to understand instinctively that charcoal fires could be adjusted to provide atmospheric conditions which simultaneously reduced copper and oxidized iron. Methods were thus evolved which allowed relatively pure copper to be separated in the molten state from iron and other unwanted materials in the ore. These when suitably oxidized could be induced to dissolve in the slag. The primary ores of copper are invariably complex sulphides of copper and iron and are generally disseminated in a porous rock such as sandstone which rarely contains more than 2 per cent by weight of copper. Such deposits were too lean to be exploited by primitive man who sought for the richer if more limited deposits produced by the weathering and oxidation of primary ores. Thus at Rudna Glava in Yugoslavia a copper mine worked in the 6th millennia did not exploit the main chalcopyrite ore body but worked instead a thin rich carbonate vein produced by leaching and weathering. This concentrated ore contained 32 per cent of copper and 26 per cent of iron. Quartz sand would have been added to such a smelting charge to ensure that most of the iron separated into the slag. At Timna in the southern Negev copper has been mined and smelted since the dawn of history. Extensive workings slag heaps and furnaces have remained with little disturbance since .