tailieunhanh - An Encyclopedia of the History of Technology part 13

An Encyclopedia of the History of Technology part 13. 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 THE LIGHT METALS ALUMINIUM AND MAGNESIUM In the middle years of the nineteenth century most of the metals in the periodic table of the elements had been chemically identified although few had been produced in the pure metallic state and engineers were still dependent upon iron and a few copper-based alloys for the construction of machinery. The metals which were used had oxides which could be reduced by carbon at atmospheric pressure. The other metals which were known could not be obtained in metallic form because of their high chemical activity. A particularly stable metallic oxide which could not be reduced was extracted from alum in 1760 and named alumina by the French chemist . By 1807 Sir Humphry Davy had concluded that even the most stable chemical compounds should be electrolytically reducible with the aid of the newly available voltaic cell and had succeeded by this approach in obtaining sodium potassium barium strontium and calcium in metallic form. For this remarkable demonstration of the power of electrochemistry Davy was awarded a prize of 50 000 francs by Napoleon. Although he failed in his endeavours to obtain the element he first named aluminum and then aluminium in metallic form it seemed evident that the other reactive metals he had obtained might well under appropriate conditions prove to be more powerful reductants than either carbon or hydrogen. In 1808 he succeeded in obtaining pure elementary boron for the first time by reducing boric oxide with electrolytically obtained potassium. The search for metallic aluminium was continued by the Danish chemist Hans Christian Oersted who in 1825 described to the Imperial Danish Society for Natural Philosophy a method of reducing aluminium chloride to metallic form with a mercury amalgam of potassium. The mercury from the amalgam was subsequently removed by distillation leaving behind a grey powder which was described as aluminium although it must have contained a good deal .