88 LIME. 



the same time, much steam and heat. This is called 

 the slaking of lime. In this process, the water unites 

 to the lime, and becomes solid ; for slaked lime is 

 quite dry. It is, therefore, called a hydrate of 

 lime. 



Lime is soluble in water : the solution has an 

 acrid taste, and is called lime-water. When lime- 

 water is exposed to the air, a stony film forms upon 

 the surface, owing to the lime attracting carbonic 

 acid, and returning to the state of carbonate, which 

 is insoluble in water. This film breaks, falls down, 

 and is succeeded by others in succession. Fresh 

 quicklime has a strong tendency to attract mois- 

 ture from the air, and also carbonic acid, so that it 

 must fye kept in closely-stopped vessels. 



Quicklime is used for making mortar for build- 

 ing, by mixing it with sand. This, by solidifying 

 the water and attracting carbonic acid, becomes a 

 very hard substance like stone. The lime should 

 be newly burnt, and the sand silicious and free from 

 impurities. It is also extremely valuable as a ma- 

 nure when put upon the land. 



Carbonate of lime is not caustic, nor soluble in 

 water. It is decomposed by the stronger acids. 

 Put chalk or marble into a vessel, and pour upon it 

 diluted sulphuric or muriatic acid ; an efferves- 

 cence will ensue, which is owing to the escape of 

 the carbonic acid. Hence these acids are em- 

 ployed to distinguish lime-stones. 



Lime combines with phosphorus, forming phos- 

 phuret of lime, to be afterwards described. With 

 sulphur it forms sulphur et of lime. 



It also combines with all the acids, forming a 

 great number of neutral salts. 



Sulphate of lime* called also gypsum, exists largely 

 in a natural state. When burnt, it forms the sub. 



