CALCIUM, a dyad metallic element. Symbol, Ca; at. wt., 40; sp. gr., 1.57; obtained by Davy by decomposing the chloride by electricity; also by heating the iodide with sodium in a closed vessel. Calcium is a yellowish white, ductile, malleable metal, which oxidizes in damp air; it decomposes water, and dissolves easily in dilute acid& Heated in the air, it melts at red hedt, and burns with a bright orange-red light. Calcium oc curs in nature chiefly as a carbonate, silicate, and sulphate. Calcium oxide, CaO, called also lime, is obtained by heating the carbonate of calcium to red ness. It is a white, earthy, infusible powder, phosphorescent at high temper atures; it is strongly alkaline, and readily absorbs carbonic anhydride. It unites vigorously with water, throwing out great heat, and forms a hydrate, Ca01-120, which is slightly soluble in cold water; it is used in medicine as lime-water. Impure lime mixed with sand forms mortar.
Calcium sulphate, CaSO4, found as hy dride of gypsum, CaSO42H2O, and sele nite and alabaster. The water is given off by heating it, and a white powder is left, which dissolves in 500 parts of cold water. Mixed with water, it sets in a hard substance; it is used under the name of plaster of Paris for making casts of medals and statues, etc.
Calcium carbonate, CaCO3, forms the chief constituent of limestone, marble, chalk, etc. It occurs crystallized as calc
spar and aragonite. Calcium carbonate is insoluble in water, but is dissolved by water containing carbonic acid gas; it is deposited from this solution by boil ing, hence boiler deposits.
Calcium phosphates occur in the bones of animals and are native in Apatite. Calcium chloride, CaCl2, is obtained by dissolving the carbonate in hydrochloric acid. It crystallizes in white prismatic crystals; it is very deliquescent. Fused calcium chloride is used to dry gases, etc. It absorbs ammonia gas.
Calcium fluoride, CaF12, occurs as fluor spar.
Calcium sulphides and phosphides have been obtained. Salts of calcium are not precipitated by H2S, either in an acid or alkaline solution. Alkaline carbonates and ammonia carbonate give a white precipitate insoluble in excess; oxalate of ammonia gives a white pre cipitate from a neutral solution; the pre cipitate is not soluble in acetic acid. A solution of sulphate of calcium gives no precipitate. The chloride gives an orange-red flame with alcohol. The spectrum of calcium gives several char acteristic lines, especially an orange-red and a green line. Chloride of lime, or bleaching powder, is a mixture of cal cium chloride and calcium hypochlorite.