LIME. Lime. common lime, quicklime, or calls. tic lime. as it is variously named, is produced by burning limestone in kilns until the carbonic acid has been driven off. The clinker resulting from this burning possesses the property of dis integration or slaking upon being treated with a sufficient quantity of water. The slaking of lime is due to its rapid hydration when in eon tact with water, and the process is accompanied by a material increase in volume and a con siderable evolution of heat. If the quantity of water be just sufficient to cause the hydration of the lime. it is reduced to a dry powder, while if the water he in excess it becomes a. paste. The slaked lime thus formed, when to a paste with water and allowed to stand in the air, has the property of hardening and firmly adhering to any surface with which it inay be in contact. This hardening of common limes will take place only in air. When lime is very pure and its activity is very great, it is known as fat lime: if the lime contains, either mixed with it or in combination, considerable amounts of inert im purities which lessen the activity of the lime, cause a partial loss of the property of slaking, and diminish its power of hardening, it is known as meagre lime: The common meth od of slaking lime consists in covering it with from two to three times its volume of water, and allowing it to stand until all the lumps are reduced and the mixture is in the con dition of a thick paste. For use in construc tion. this paste is mixed with from two to three times its volume of sand, when it is called lime mortar. The process of hardening of lime mor tar consists in the gradual formation of car bonate of liine through the absorption of car lionie acid from the air. accompanied by the crystallization of the mass of hydrated lime as it gradually dries out. The hardening, process is a slow one at best, and the lime mortar used in the interior of thick masses of masonry, where the air cannot. get at it, will take years to become bard. Lime mortar should be used only in masonry exposed to the air. See BuiLnixo.
11IDRAI'Lle LIME. 11ydratilie lime is Obtained by burning limestone containing enough silica and alumina to impart to it the ability to hard en tinder water. In calcination the silica and alumina edunbine with a portion of the lime to form silicates and ;Humiliates of lime, leaving the remainder of the lime as free lime in an micombined state. When treated with water
the free lime is slaked. The manufacture of hydraulic lime is practically confined to Europe, and consists, after the quarrying of the rock, of burning. slaking, and bolting the material. The burning is accomplished in kilns. and is a proc ess requiring considerable skill and careful at tention. To slake the clinker it is spread in layers from four inches to eight inches deep and sprinkled with water. The object is to slake the free lime without hydrating the silicates and aluminates. -After the has been reduced to powder by slaking,. it is passed through sieves and packed for shipment. 'Hydraulic lime is in the same manner as common lime, being mixed ith Walter and sand to a paste. When in the air hydraulic lime acts like common Hine.
carbonic acid. drying. and harden ing. In water the action of hydraulic lime is altogether different from that of common lime. since, owing to the presence of the silicates and alumni:adds of lime, the hydraulic lime hardens under water, while the common lime does not. 'HYDRAULIC CEMENT. 'Hydraulic cements are classified as natural cements, Portland (dements. and puzzolanic cements. Natural crnic»I is the prodnet, obtained by calcining at a low tempera ture a natural limestone Witliollt plliVerization or admixture of other materials, and finely grinding the clinker. In Europe these eel wilts are called Homan cements, and they wore first manufactured in England in 179i, by ;lames Parker. Natural cements began to he manufac tured in France about 1825: in the mailed States natural-cement rock was discovered while build ing the Erie Canal in New York, in ISIS. France and the United States are the principal pro ducers of natural cement. their respective out puts being 2.000.000 barrels and S.S00,000 barrels annually. The principal centres of natural-ce ment manufacture in the United States are Ulster County, N. Y.; Cumberland, Aid.; Louis ville, Ky.: :\lilwaukee. Wis.: and Utica, Ill. The rook employed is an argillaceous limestone. The process of manufacture consists in mining and quarrying this limestone: breaking it into lumps about the size of one's hand; calcining these lumps with coal in kilns, and finally crushing and grinding the clinker. Natural cements are characterized by a very rapid set and slowness in wining strength subsequently: they have less strength than Portland conical.