Calcium

kal'si-um, an important chemical element. It ranks fifth among the elements in point of abundance, making up about four per cent of the earth's crust. It forms an important part of lime, limestone, marble, plaster of Paris, chalk, shell, pearl, bone, egg shells, coral, and glass. It is present in all hard water. It was obtained free from other elements in 1808 by Sir Humphry Davy. In a pure condition it is a silver-white metal with a brilliant luster. Ordinarily, however, It is harder than lead and somewhat softer than gold. Calcium is a caustic. It unites chemically with nearly all of the elements, possibly all except argon. Calcium burns in oxygen with a brilliant white flame known as a limelight, Drummond's light, etc. The world requires about 100 tons of pure calcium yearly. See Lime; Limestone