362 Agricultural Chemistry. 



ment of many forms of micro-organisms, which are so necessary 

 to the formation of available plant food. 



Lime for agricultural purposes is put upon the market in 

 several different forms: as caustic lime; as hydrate of lime or 

 water-slaked lime; as air slaked lime or carbonate of lime; as 

 ground limestone rock and as ground oyster or clam shells. The 

 caustic or quick lime is the most concentrated form and the most 

 active. It is made up of the two elements, calcium and oxygen. 

 When they unite we have quick lime, or calcium oxide, and this 

 material when united with carbon dioxide forms calcium car- 

 bonate, the chief constituent of limestone and oyster and clam 

 shells. When limestone is burned quick-lime or calcium oxide 

 is left behind. One hundred pounds of pure calcium carbonate 

 will yield on burning 56 pounds of calcium oxide, and 44 pounds 

 of carbon dioxide will be driven off. From the quick lime, the 

 slaked lime is obtained by addition of water out of contact with 

 the air. Fifty-six pounds of caustic become 76 pounds of slaked 

 lime. When contact of air is allowed the 56 pounds of caustic 

 become 100 pounds of air slaked lime by again combining with 

 the carbon dioxide of the air. Thus it will be seen that in 

 purchasing lime it will be more economical to buy the caustic or 

 quick lime. However, because of its quick action, care must be 

 exercised in its use. Finely ground limestone is coming into 

 high favor and where it can be obtained at a sufficiently low cost 

 is undoubtedly the safest form to use, especially by the inex- 

 perienced. Lime should be applied to the surface and if pos- 

 sible thoroughly incorporate with the few upper inches of the 

 soil. The clovers and other leguminous plants require more 

 lime than do the cereals and are much more sensitive to acidity 

 of the soil. A good stand of clover, therefore, is an indication 

 that the soil contains sufficient lime. 



Gypsum or land plaster is a sulphate of lime and has given 

 excellent results with clover and other leguminous plants. It 

 is now generally believed that its beneficial action is due to the 

 fact that the plaster sets free the unavailable potash of the soi 



