classes
described above.

It is important that this distinction should be well understood by the
learner, as the words "mechanical" and "chemical" in connection with
manures will be made use of throughout the following pages.

[What are absorbents?

What kind of manure is charcoal?]

There is another class of manures which we shall call _absorbents_.
These comprise those substances which have the power of taking up
fertilizing matters, and retaining them for the use of plants. For
instance, _charcoal_ is an absorbent. As was stated in the section on
soils, this substance is a retainer of all fertilizing gases and many
minerals. Other matters made use of in agriculture have the same effect.
These absorbents will be spoken of more fully in their proper places.

TABLE.

MECHANICAL MANURES are those which improve the mechanical condition of
soils.

CHEMICAL " are those which serve as food for plants.

ABSORBENTS are those substances which absorb and retain
fertilizing matters.

[Into what classes may manures be divided?

What are organic manures?

Inorganic? Atmospheric?]

Manures may be divided into three classes, viz.: _organic_, _inorganic_,
and _atmospheric_.

ORGANIC manures comprise all _animal_ and _vegetable_ matters which are
used to fertilize the soil, such as dung, muck, etc.

INORGANIC manures are those which are of a purely _mineral_ character,
such as lime, ashes, etc.

ATMOSPHERIC manures consist of those organic manures which are in the
form of gases in the atmosphere, and which are absorbed by rains and
carried to the soil. These are of immense importance. The ammonia and
carbonic acid in the air are atmospheric manures.

FOOTNOTES:

[U] Silicate of potash.

CHAPTER II.

EXCREMENTS OF ANIMALS.

[Of what is animal excrement composed?

Explain the composition of the food of animals.

What does hay contain?

To what does Liebig compare the consumption of food by animals, and
why?]

The first organic manure which we shall examine, is animal _excrement_.

This is composed of those matters which have been eaten by the animal as
food, and have been thrown off as solid or liquid manure. In order that
we may know of what they consist, we must refer to the composition of
food and examine the process of digestion.

The food of animals, we have seen to consist of both organic and
inorganic matter. The organic part may be