58 Journal of the Mitchell Society [October 



necessary in retainifig tlie moisture in the soil during drj 

 weather. It also increases the permeabilitj of the soil for air. 

 l^earlj all forms of lime readily improve the soil structure. 



For sandy soils a small amount of lime carbonate will serve 

 to make the structure slightly more compact by cementing some 

 of the particles together, thereby improving the power of the 

 soil to hold capillary water and preventing its drying so readily. 



;- FOEMS OF LIME 



In nature the chief source of "lime" is the common mineral 

 calcite which occurs extensively as beds of fossils shells, often 

 not distinguishable, and these beds according to their j)urity, 

 the degree of consolidation, method of deposition, subsequent 

 changes, and to the kind and nature of the contributing organ- 

 isms, are classified as limestones, marls, chalk, marble, etc. 



This material is applied to the soil in three forms ; decayed 

 limestone, marl, etc., these substances (CaCOg) ground, and 

 that which has been burned at a high temperature. In the 

 process of burning, a gas (carbon dioxide, CO2) is given off 

 and calcium oxide (CaO), quicklime, remains. When quick- 

 lime is allowed to slack slowly in dry air, it again assumes the 

 form of a carbonate and is called air-slaked lime. If water be 

 added to the quicklime, the mixture forms calcium hydrate, 

 Ca(0II)2, and is known as water-slaked or hydrated (caustic) 

 lime. If the slaking take place in damp air, the quicklime 

 absorbs from the air some moisture and some carbon dioxide 

 the result being a mixture of lime carbonate and hydrated lime. 



Belated Forms. — Dolomite is a calcium magnesium carbon- 

 ate (CaCOg, MgCOo), sometimes incorrectly called magnesian 

 limestone. It occurs extensively in the Appalachian Mountains 

 and is found in Virginia, Tennessee, ISTorth Carolina, Georgia, 

 and Alabama, where it is frequently called "marble." 



Gypsum, the hydrated sulfate of calcium (CaS04, 2II2O), is 

 ground and sold on the market as "Land Plaster." 



