17

and two-tenths of one per cent, in others. But a very small quan-
tity is absolutely necessary.

Soda.—Soda, the oxyd or rust of a metal called sodium, is an-
other of the necessary constituents of a fertile soil. It has nearly
the same uses as potash, and may be substituted for it to a certain
extent. It exists in various proportions in soil, but a very small
quantity seems to be all that is necessary.

On salt water, land produces wheat with bright, strong straw—
whilst land remote from it, with an equal quantity of inorganic
matter, will not do this, because it is not supplied with soda from
the atmosphere.

Phosphoric Acid, is also one of the necessary constituents of
a fertile soil. With lime and magnesia it forms about fifty per
cent, of the bones of animals. Its elements are also found in the
blood and brain, and in combination with different bases; it forms
a very large proportion of all grains that are used for food. It
exists in the soil, in combination with lime, magnesia, iron and
alumina. With those substances, and others of this class, it forms
salts, which are called phosphates. Unless there be this substance
present in a soil, in sufficient abundance, and in proper form for
use, no matter how rank or strong the crop of straw may be, there
will be no corresponding yield of grain. Hence, in soils famous
for large crops of straw, with a small quantity of grain, the farmer
may increase it by the application of manures containing this sub-
stance, which are principally Bone Dust, Super-phosphate of
Lime and Mexican Guano.

Sulphuric Acid.—Sulphuric acid (commonly called Oil of
Vitriol,) is also a necessary constituent of fertile soils. It most gen-
erally exists in combination with lime, forming with two equivalents
of water, that which is generally known as gypsum. Its elements
exist in all plants, and in the blood of all animals.

The quantity necessary to constitute a fertile soil, is very small.
This has been shown by numerous practical experiments, as well
as by many analyses.

Besides the soil, the air undoubtedly supplies the plants some
portion of the two substances named above, or rather supplies the
elements from which they are formed.

All animal and vegetable bodies, by their putrefaction, give rise
to volatile compounds, containing sulphur and phosphorus, and un-
der conditions which we know to exist, these compounds are
changed into phosphoric and sulphuric acid, which, with bases,
will form phosphates and sulphates. Although these two sub-
stances have not, as yet, been detected in atmospheric air, yet we
know that they must exist there, and will be brought down by
dew, rain, and snow, to the surface of the earth.
2