Chlorine.—Chlorine is another of the necessary constituents
of a fertile soil. In its pure state, it "is a yellowish, green colored
gas, which has an astringent taste, and a disagreeable odor."
When breathed, it excites violent spasm of some of the upper parts
of the wind-pipe, and has a very irritant effect on the organs of
respiration, even when very much diluted with air. In the soil it
is almost always united to soda, and very rarely to lime, magnesia
or potash. United to any of the bases, it loses its poisonous
properties. With soda it forms the different kinds of common
table salt. It is believed to add to the weight of the grain.

The above compose all of the substances necessary to consti-
tute a fertile soil. In some soils, manganese is found, which is
the oxyd or rust of a metal called manganesium. This, though
occasionally found in fertile soils, and in the ashes of plants grow-
ing on them, yet is not essential, since its presence does not in-
crease, nor its absence decrease the productiveness of a soil.

The air, in common with the vegetable matter in a soil, fur-
nishes to plants, carbonic acid, out of which they form woody
fibre, and all substances in them which contain charcoal.

Besides this, it in common with many manures, affords ammo-
nia, a substance which supplies a great share of the nutritious
parts of plants, and constitutes, by its elements, a large part of
the mass of the bodies of the vegetable and animal creation.

Water is supplied, in this country at least, wholly from the at
mosphere, in the form of dew or rain.

To recapitulate, then, we have as food for plants furnished by
the soil alone:—

Silica or sand,           Magnesia,

Alumina or clay, Potash,
Iron,                          Soda,

Lime,                        Chlorine.

We have furnished in a great measure by the soil, but partly
also by the air:

The elements of Phosphoric acid—

The elements of Sulphuric acid.

In localities adjacent to the ocean, bay, or indeed any salt wa-
ter, there is always present in the air, both soda and chlorine in
the form of common salt.

We have furnished in a great measure by the air, but partly
also by the soil:—

Carbonic acid containing carbon—

Ammonia containing nitrogen, and

Water.

These contain all of the elements necessary to the perfection of
vegetable and animal life. Those of them which are not present
in the soil in sufficient quantities, and which cannot be derived