quick state. If water be thrown upon it when in this
condition, it becomes hot, swells up, and falls to a fine soft powder,
and has then entered into combination with water. If it be exposed to
the air, the same action takes place, although, of course, more slowly;
and if it be left for a sufficient time, it at length absorbs carbonic
acid, and reverts to its original form of carbonate of lime, although
now in a state of very fine division.

While lime may be applied in the state of carbonate, either as chalk,
marl, or pounded limestone, and with a certain amount of advantage, much
greater effects are obtained from the use of lime itself in the quick or
slaked state. These advantages are dependent partly on the mechanical
effect of the burning and slaking, which enable us to reduce the lime to
a much more minute state of division, and consequently to incorporate it
more uniformly and thoroughly with the soil, and partly on the more
powerful chemical action which it exists when in the quick or caustic
state. Other minor advantages are also secured, such as the production
of a certain quantity of sulphate of lime, produced by the oxidation of
the sulphur of the coal used in burning, etc., which, though
comparatively trifling, may, under particular circumstances and in some
soils, be of considerable importance.

The action of lime is of a complicated character. Where the soil is
deficient in lime, it must necessarily act by supplying that substance
to the plants growing in it. But this is manifestly a very subordinate
part of its action,--_1st_, Because no soil exists which does not
contain lime in sufficient quantity to supply that element to the
plants. _2d_, Because its effects are not restricted to those soils in
which it exists naturally in small quantity; and, _3d_, Because it is
found that a small application, such as would suffice for the wants of
the crops, is not sufficient to produce its best effects.

It is a familiar fact that the quantity of lime applied to the soil for
agricultural purposes is very large, as much as ten, and even twenty
tons per acre having been used, while the smallest application is
exceedingly large when compared with the mere requirements of the crops.
Of late years the very large applications once in use have become less
common, as it has been found preferable to employ smaller doses more
frequently repeated. The quantity used depends, however, to a great
extent, on the nature and con