luble
silicates, it is well known that grain, etc., grown on it, not being
able to obtain the material which gives them strength, will fall down or
_lodge_; but, if such measures be taken, as will render the sand
soluble, the straw will be strong and healthy. Alkalies used for this
purpose, come under the head of those manures which develope the natural
resources of the soil.

Again, much of the mineral matter in the soil is combined within
particles, and is therefore out of the reach of roots. Lime, among other
thing, has the effect of causing these particles to crumble and expose
their constituents to the demand of roots. Therefore, lime has for one
of its offices the development of the fertilizing ingredients of the
soil.

3d. Those manures which improve the mechanical condition of the soil.

The alkalies, in combining with sand, commence their action on the
surfaces of the particles, and roughen them--_rust_ them as it were.
This roughening of particles of the soil prevents them from moving among
each other as easily as they do when they are smooth, and thus keeps the
soil from being compacted by heavy rains, as it is liable to be in its
natural condition. In this way, the mechanical texture of the soil is
improved.

It has just been said that _lime_ causes the pulverization of the
particles of the soil; and thus, by making it finer, improves its
mechanical condition.

Some mineral manures, as plaster and salt, have the power of absorbing
moisture from the atmosphere; and this is a mechanical improvement to
dry soils.

[Name some mineral manures which absorb ammonia?]

4th. Those mineral manures which have the power of absorbing ammonia.

_Plaster_, _chloride of lime_, _alumina_ (_clay_), etc., are large
absorbents of ammonia, whether arising from the fermentation of animal
manures or washed down from the atmosphere by rains. The ammonia thus
absorbed is of course very important in the vegetation of crops.

Having now explained the reasons why mineral manures are necessary, and
the manner in which they produce their effects, we will proceed to
examine the various deficiencies of soils and the character of many
kinds of this class of fertilizers.

CHAPTER IX.

DEFICIENCIES OF SOILS, MEANS OF RESTORATION, ETC.

As will be seen by referring to the analyses of soils on p. 72, they
may be deficient in certain ingredients, which it is the object of
mineral manures to supply. These we will take up i