|
30. ZincName: Zinc
Zinc is a bluish-white, lustrous metal. It is brittle at ambient temperatures but is malleable at 100 to 150°C. It is a reasonable conductor of electricity, and burns in air at high red heat with evolution of white clouds of the oxide. Zinc-deficient animals require 50% more food to gain the same weight of an animal supplied with adequate amounts of zinc. Zinc is not particularly toxic and is an essential element in the growth of all animals and plants. Plating thin layers of zinc on to iron or steel is known as galvanising and helps to protect the iron from corrosion. Zinc alloys have been used for centuries, as brass goods dating to 1000-1400 BC have been found in Palestine and zinc objects with 87% zinc have been found in prehistoric Transylvania. Because of the low boiling point and chemical reactivity of this metal (isolated zinc would tend to go up the chimney rather than be captured), the true nature of this metal was not understood in ancient times. Smelting and extraction of impure forms of zinc was being accomplished as early as AD 1000 in India and China. By the end of the 14th century, the Hindus were aware of the existence of zinc as a metal separate from the seven known to the ancients. In the West, the discovery of pure metallic zinc is most often credited to the German Andreas Marggraf, in the year 1746, though the whole story is considerably more involved. Descriptions of brass manufacture are found in Western Europe in the writings of Albertus Magnus, c. 1248, and by the 16th century, the understanding and awareness of the new metal broadened considerably. Agricola observed, in 1546, that a white metal could be condensed and scraped off the walls of a furnace when zinc ores were smelted. He added in his notes that a similar metal called "zincum" was being produced in Silesia. Paracelsus (died 1541) was the first in the West to say that that "zincum" was a new metal and that it had a separate set of chemical properties from other known metals. The upshot is that zinc was known by the time Marggraf made his discoveries and in fact zinc had been isolated two years earlier by another chemist, Anton von Swab. However, Marggraf's reports were exhaustive and methodical and the quality of his research cemented his reputation as the discoverer of zinc. Before the discovery of the zinc sulfide flotation technique, calamine was the mineral source of zinc metal. Metallic zinc is not considered to be toxic, but there is a condition called zinc shakes or zinc chills that can be induced by the inhalation of freshly formed zinc oxide. Excessive intake of zinc can promote deficiency in other dietary minerals. Quick links
|