MINERAL FERTILIZERS. y t 



159. Lime, or calcium oxide, is made by heating 

 common limestone in a suitable kiln. This mineral, 

 when pure, consists of lime in combination with car- 

 bon dioxide, or carbonic-acid gas. The rock is bro- 

 ken into small-sized pieces, placed loosely in what 

 is known as a kiln, and, by means of wood or coal, 

 thoroughly heated until the carbon dioxide is driven 

 off. Calcium oxide, or quicklime, is left. One hun- 

 dred pounds of pure limestone yield fifty-six pounds 

 of lime. 



1 60. If water be poured on quicklime, a portion 

 of the water will combine with it, giving out heat, 

 and forming slaked lime. The same result will be 

 produced by exposing the quicklime to moist air. 

 Long exposure to air will result in a reunion of car- 

 bon dioxide with the lime. The new carbonate 

 will be in a finely divided condition, which is better 

 for fertilizing purposes than the original limestone, 

 though not so good as the slaked lime (30). 



161. One hundred pounds of quicklime (also 

 called caustic lime) unite with thirty-two pounds of 

 water in the process of slaking. This water is not 

 mixed with the lime, but forms a chemical compound 

 known as calcium hydroxide. This hydroxide is 

 slighty soluble in water, of caustic taste, and when 

 mixed with sand forms common mortar. The hard- 

 ening of mortar is due to the absorption of carbon 

 dioxide from the air, and a gradual union of the lime 

 with the silica, or sand. 



162. The application of lime to soils furnishes at 



