Calcium (symbol: Ca atomic number: 20 ) Lime was prepared by the Romans in the first century under the name calx, but the metal was not discovered until 1808. After learning that Pontin and Berzelius prepared calcium amalgam by electrolyzing lime in mercury, Davy was able to isolate the impure metal. Calcium is a silvery metallic alkaline earth element, fifth in abundance in the earth's crust (3%). It is an essential constituent of bones, leaves, teeth, and shells. In combined form, it occurs abundantly in minerals as gypsum, limestone and fluorite. It is used as an alloying agent for aluminum, beryllium, copper, lead, and magnesium alloys. CaO, which is made by heating limestone that is changed into slaked lime by carefully adding water, is the great base of chemical refinery with countless uses. Mixed with sand it hardens as mortar and plaster by taking up carbon dioxide from the air.The solubility of the carbonate in water containing carbon dioxide causes the formation of caves with stalagtites and stalagmites and is responsible for hardness in water.
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