Calcium (Lat. calx, lime), the metallic basis of lime. It is one of the most abundant and important constituents of the crust of the globe, occurring as limestone, gypsum, fluor spar, and phosphates, and in the animal kingdom making up the solid part of the bone. The metal is not found in nature in its pure state, but always in combination. Sir Humphry Davy first prepared the metal in 1808, but not in sufficient quantity to thoroughly investigate its properties; Several methods have been proposed for the isolation of calcium, among which the following are most worthy of mention. Matthiessen employed the electrolytic decomposition of a mixture consisting of two equivalents of chloride of calcium and one equivalent of chloride of strontium. Lies-Bodart obtained it still more easily by fusing iodide of calcium with an equivalent quantity of sodium; and Caron performed the reduction of the chloride by means of zinc. Calcium is a light, yellowish metal, of the color of gold alloyed with silver. In hardness it is intermediate between lead and gold; it is very malleable, and can readily be hammered into leaves thinner than writing paper.

It decomposes water rapidly, with liberation of hydrogen, melts at red heat, and burns to lime with a brilliant light and yellow flame, and is a poor conductor of electricity. Calcium fused with a large excess of zinc forms an alloy, CaZn12, which crystallizes in quadratic octahedrons of sp. gr. 6.37, and is readily decomposed by water. The equivalent of calcium is 20, its symbol Ca. The calcium light, commonly called Drummond light, is produced by the action of the oxyhydro-gen flame on perfectly pure lime, made free from silica by precipitation and afterward calcined and pressed into moulds. - The most important salts of calcium will be treated of under their familiar names.