LIME (O. Eng. lim,

See also:

• LAT

Lat. limes, mud, from linere, to smear)  , the name given to a viscous exudation of the holly-tree, used for snaring birds and known as " bird-lime." In chemistry, it is the popular name of calcium oxide, CaO, a substance employed in 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 CEMENT, CONCRETE and MORTAR, for details . Pure calcium oxide " quick-lime," 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 crumbling to pieces; this operation is termed " slaking " and the resulting product " slaked lime "; it is chemically equivalent to the conversion of the oxide into hydrate . A solution of the hydrate in water, known as lime-water, has a weakly alkaline reaction; it is employed in the detection of carbonic acid . " Milk of lime " consists of a cream of the hydrate 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, &c . 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 . Calcium phosphate is much employed in treating rickets, and calcium chloride in haemoptysis and haemophylia .

It is an antidote for

mineral and oxalic acid poisoning .