LIME, the name given to a viscous exudation of the holly tree, used for snaring birds and known as "bird-lime" (0. Eng. Urn, Lat. limes, mud, from limere, to smear) ; the popular name of calcium oxide or "quick-lime," a substance employed since very early times as a component of mortars and cementing materials.
It is prepared by the burning of limestone (a process described by Dioscorides and Pliny) in kilns similar to those described under CEMENT. The value and subsequent treatment of the product depend on the purity of the limestone; a pure stone yields a "fat" lime which readily slakes ; an impure stone, especially if magnesia be present, yields an almost unslakable "poor" lime. (See CE MENT, CONCRETE and MORTAR, for details.) Pure calcium oxide, CaO, obtained by heating the pure carbonate, is a white amorphous substance, which can be readily melted and boiled in the electric furnace, cubic and acicular crystals being deposited on cooling the vapour. It combines with water, evolving much heat and crum bling to pieces; this operation is termed "slaking" and the resulting product "slaked it is chemically equivalent to converting the oxide into hydroxide. An aqueous solution of the hydroxide,
known as lime-water, has a weakly alkaline reaction; it is em ployed in the detection of carbonic acid. "Milk of lime" consists of a cream of the hydroxide and water. Dry lime has no action upon chlorine, carbon dioxide and sulphur dioxide, although in the presence of water combination ensues. In medicine lime-water, applied externally, is an astringent and desiccative, and it enters into the preparation of linamentum calcis and carron oil which are employed to heal burns, eczema, etc. Applied internally, lime water is an antacid; it prevents the curdling of milk in large lumps (hence its prescription for infants) ; it also acts as a gastric sedative. It is an antidote for mineral and oxalic acid poisoning (see also CALCIUM).