EXTENSION COURSE IN SOILS. 65 
of lime are different compounds of the element calcium, and any one 
of them will neutralize the acidity of soils. The carbonate occurs in 
different forms, among which are limestones, marl, chalk, shells of 
mussels, and refuse lime from sugar-beet factories. (Ref. No. 5, 
pp. 160-182.) Any of these forms of calcium carbonate when ground 
sufficiently fine are well adapted for use in correcting soil acidity. 
Not only does this form of lime have a good effect upon the soil, 
but it is relatively convenient to handle. Whenever it can be applied 
at a reasonable price as compared with other forms of lime it should 
generally be used. 
Quicklime, sometimes called lump lime, results from the burning 
of limestone. In the process of burning carbon dioxid is driven 
from the limestone as a gas, leaving the quicklime, chemically, 
calcium oxid, in lump form. Quicklime, like the forms of calcium 
carbonate, should be finely divided before it is mixed into the soil. 
This form of lime is caustic and disagreeable to handle. 
Water-slaked or hydrated lime results from adding water to 
quicklime. This process produces a great deal of heat and causes a 
chemical reaction which results in the formation of calcium hydroxid. 
Hydrated lime is finely pulverized and, from this standpoint, is in 
good condition to apply to the soil. Quicklime is sometimes spread 
without grinding or slaking, and, if done during a rainy season, 
will soon become slaked by the water which falls upon it. In this 
case it is advisable to spread it more thoroughly by harrowing 
before working it into the soil. 
Slaked lime, like quicklime, is caustic. It is not advisable to use 
these forms in excessive quantities, particularly on light soils deficient 
in organic matter, since they unduly hasten the breaking down of 
the vegetable matter of the soil. This process is accompanied by an 
increased formation of nitrates, which may be obvious in growing 
plants, but with a corresponding depletion of the soil, especially if 
the growing crop is nonleguminous. Caustic lime gradually unites 
with carbon dioxid and is thus converted into the carbonate. When 
heavy applications of caustic lime are mixed with sandy soils, 
a cementing of the sand grains sometimes takes place, causing a 
detrimental clodding condition. On the other hand, liberal applica- 
tions of caustic lime produce a flocculating effect upon clay soils, 
which reduces clods and improves soils physically. 
No harm can come to the soil from the use of any form of calcium 
carbonate, even in large applications, but it should be noted that 
large quantities of lime in any form are favorable to the scab of pota- 
toes. The form and quantity of lime to use is a practical question 
depending primarily on the degree of acidity of the soil and the rel- 
ative cost of available materials. The cost depends on grade of 
21862°— Bull. 355—16 5 
