CALCIUM. 59 



Oxide of Calcium, or Quicklime, is composed 

 of one equivalent or 20 parts of calcium, com- 

 bined with one equivalent or 8 parts of oxygen. 



Carbonate of Lime, or Limestone, is composed 

 of oxide of calcium, combined with carbonic 

 acid. When pure, 'every 100 Ibs. of limestone 

 contain 44 Ibs. of carbonic acid, and 56 of 

 oxide of calcium; so that one ton of pure 

 limestone contains 1H cwt. of oxide of calcium, 

 or when burnt an equal amount of quicklime. 

 Limestones generally contain a sensible quantity 

 of mineral matter, as silica, magnesia, alumina, 

 and oxide of iron, with traces of phosphoric acid, 

 and sometimes potash and organic matter. This 

 foreign matter, in the best quality of limestones, 

 does not often exceed five per, cent. When lime- 

 stones are burnt, the carbonic acid is expelled, 

 and the lime is left in the caustic state, as quick- 

 lime. When water is applied to quicklime 

 great heat is developed, the lime swells and 

 cracks, and finally falls to a fine bulky white 

 powder. When quicklime is left in the open 

 air, it gradually absorbs water from the atmos- 

 phere, and finally falls into a fine powder. In 

 rich lime the increase of bulk by slaking may 

 be 3 to 3i times. 



Quicklime on combination with water is con- 

 verted into hydrate of lime. This hydrate 

 consists of 75. 68 Ibs. of lime, and 24. 32 Ibs. of 



