LIME. The oxide of calcium, one of the metals of the earths. This very use ful earth is obtained by exposing chalk and other kinds of limestone, or carbon ates of lime, to a red heat—an operation generally conducted in kilns constructed for the purpose ; the carbonic acid is thus expelled, and lime, more or less pure, according to the original duality of the limestone, remains. In this state it is usually called quicklime. When sprinkled with water it becomes very hot, and crumbles down into a dry powder, called slaked lime, or hydrate of lime. When exposed for some weeks to the air it also falls into powder, in consequence of the absorption of moisture, and of a portion of carbonic acid; so that, in this case, part of the lime gradually reverts to the state of carbonate, and loses its causticity. Pure lime may be obtained by heating powdered Carrara marble to whiteness in an open crucible. It is white, very fusible, highly luminous when heated to fall red ness, and of a specific gravity of about 2.8. It requires for solution about 500 parts of water, and is somewhat more soluble in cold than in hot water. But, weak as this solution is, it acts powerfully alkaline upon vegetable colors, and has an acrid taste ; hence the term alkaline earth applied to lime. It absorbs car bonic acid by exposure to air, and as car bonate of lime is insoluble in water, it be comes milky in consequence ; so that, from this property, lime-water is a useful test of the presence of carbonic acid. The nature of lime was first demonstrated by Davy in 1807: he showed that, like the other alkalies, it was a metallic oxide. The metallic base of lime has been termed calcium: its equivalent is 20, and lime, being a compound of one atom of calcium, and one of oxygen, is represented by the equivalent number 28; and hydrate of lime by 28 lime + 9 water = 87. The salts of lime are generally obtained by dissolving carbonate of lime in the re spective acids : several of them exist native. Sulphate of lime, selenite, or gypsum, is an abundant natural product, and may be formed artificially by adding sulphuric acid, or the soluble sulphates, to solutions of the salts of lime. It con sists of 28 lime -I- 40 sulphuric acid, and its crystals include two atoms =18 of water. When these crystallized sul phates of lime are heated, they part with their water and fall into a white powder, called plaster of Paris when this is mixed with water it again combines with it, and concretes into a white mass ; hence its use for casts, busts, &c. Sul
phate of lime is often contained in spring water, which is thus rendered hard and unfit for washing. These waters become turbid upon the addition of a spirituous solution of soap. .Pho,Thate of lime is found native, constituting the mineral called apatite : this is a subphosphate, composed of 8 equivalents of line= 84, and 2 of phosphoric acid = 72. The earth of bones is also chiefly a similar phos phate of lime. Oxalate of lime is very insoluble, and is precipitated whenever oxalic acid or a solution of oxalate is added to solutions containing lime ; hence it is that oxalate of ammonia is so valuable a test of the presence of lime, and is frequently used tbr the purpose of separating lime in analysis. When oxa late of lime is well dried, at it is anhydrous, and consists of 28 lime + 86 oxalic acid= 64 oxalate of lime. This substance is occasionally found in the human urine, and sometimes forms cal culi. These are often of a reddish brown color and a rough exterior, whence they have been termed mulberry wields. When hydrate of lime is exposed to chlorine, the gas is absorbed, and a chlo ride of lime is obtained. This article is manufactured upon an extensive scale, under the name of bleaching powder. It evolves chlorine when acted upon by acids ; and gives it out very slowly when exposed to air, in consequence, probably, of the absorption of carbonic acid. It is a most useful disinfecting material, and, when dissolved in water, forms bleaching liquid. Carbonate of lime is thrown down when alkaline carbonates are added to solutions of the salts of lime. It is a most abundant natural product, and is found pure in the varieties of calcareous spar and statuary marble. Chalk and several varieties of limestone are also nearly pure carbonates of lime. It is easily distinguished from other minerals by effervescing in dilute muriatic acid, and by yielding quicklime when a frag ment is heated before the blowpipe. It is constituted of 28 lime + 22 carbonic acid ; the equivalent, therefore, of car bonate of lime is 50.