Improvers for chalky soild

1227. Calcareous soils are also generally improved by burning. Soil that is formed of pure carbonate of lime is barren and unfruitful, but when mixed with sand and a little clay, it forms a calcareous loam. If calcareous loam, or even pure carbonate of lime, be burnt, the carbonic acid is expelled from it; and if exposed to the atmosphere in this state, the pure lime which it contains rapidly reabsorbs from the air the carbon which was expelled from it by burning, in the form of carbonic acid gas, crumbling down at the same time into a fine powder, so as to become intimately mixed with the soil.