It exhausts the organic parts of the soil, by decomposing them, and resolving them into the gases and minerals of which they are composed. If the soil do not contain a sufficient quantity of absorbent matter, such as clay or charcoal, the gases arising from the organic matter are liable to escape; but when there is a sufficient amount of these substances present (as there always should be), these gases are all retained until required by the roots of plants. Hence, although the organic matter of manure and vegetable substances may be _altered in form_, by the use of lime, it can escape (except in very poor soils) only as it is taken up by roots to feed the crop, and such exhaustion is certainly profitable; still, in order that the fertility of the soil may be _maintained_, enough of organic manure should be applied, to make up for the amount taken from the soil by the crop, after liberation for its use by the action of the lime. This will be but a small proportion of the organic matter contained in the crop, as it obtains the larger part from the atmosphere. The only way in which lime can exhaust the inorganic part of the soil is, by altering its condition, so that plants can use it more readily. That is, it exposes it for solution in water. We have seen that fertilizing matter cannot be leached out of a good soil, in any material quantity, but can only be carried down to a depth of about thirty-four inches. Hence, we see that there can be no loss in this direction; and, as inorganic matter cannot evaporate from the soil, the only way in which it can escape is through the structure of plants. [If this course be pursued, will the soil suffer from the use of lime? Is it the lime, or its crop, that exhausts the soil? Is lime containing magnesia better than pure lime? What is the best kind of lime?] If lime is applied to the soil, and increases the amount of crops grown by furnishing a larger supply of inorganic matter, of course, the removal of inorganic substances from the soil will be more rapid than when only a small amount of crop is grown, and the soil will be sooner exhausted--not by the lime, but by the plants. In order to make up for this exhaustion, it is necessary that a sufficient amount of inorganic matter be supplied to compensate for the increased quantity taken away by plants. Thus we see, that it is hardly fair to accuse the _lime_ of exhausting the soil, when it only improves its character, and increases the amount of its yield. It is the _crop_ that takes away the fertility of the soil (the same as would be the case if no lime were used, only faster as the crop is larger), and in all judicious cultivation, this loss will be fully compensated by the application of manures, thereby preventing the exhaustion of the soil. [Is the purchase of marl to be recommended? How is lime prepared for use? (Note.) Describe the burning and slaking of lime.]