250 



LIME 



but in water saturated with carbon dioxide at ordinary 

 temperature it is soluble as calcium bicarbonate to the 

 extent of one part in about 1000 parts. The less carbon 

 dioxide present, the less calcium carbonate is dissolved. Soil 

 moisture contains small quantities of carbon dioxide. This 

 would change calcium hydroxide dissolved in it to carbonate, 

 a change which takes place very quickly. Further quantities 

 of carbon dioxide would change the carbonate to bicarbonate 

 and so dissolve it. Since carbon dioxide is being constantly 

 produced in the soil, the change of hydroxide to carbonate 

 and bicarbonate is fairly rapid. On account of this double 



Fig. 62. — Pile of air-slaked lime. (Hibshman.) 



change of hydroxide, it makes very little difference which 

 form is used on soils, whether fresh slaked lime, air-slaked 

 lime, or limestone. Burnt lime has a caustic effect on plant 

 growth, and is said to cause rapid decay of organic matter 

 in the soil; consequently it should be used with great care 

 and never should be applied near seeding time. Due to a 

 difference in physical condition, or more accurately stated, 

 due to a difference in molecular arrangement, there is a 

 difference in the solubilitv of various carbonates. Shell 

 marl, oyster shells, limestone, is the order of solubility of 

 these carbonates. For practical purposes, however, it may 

 be said again that the availability of all forms of lime is 



