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the soil. As the growing crop can only use such materials as are
already in, or can be reduced to a soluble state, whatever can
conduce to the state of solution, will benefit them. The finer the
grains of sand, the more easily they are acted on by atmospheric
agency, and the more speedily will they yield whatever substances
they may contain. But there is another, and a very great differ-
ence in the value of coarse and fine sand. A large part of the
food of plants is derived from the atmosphere. This food must be
absorbed wholly by the soil, in the early growth of the plant; and
if the soil has not the power of absorption, the plant will pine, lan-
guish and die, unless it be supported by applied manures. Sand,
in a very fine state of division, has powerful absorbent qualities, it
absorbs and retains atmospheric food for plants, and to a very
great extent, supplies the place of alumina (clay), the peroxyd of
iron, and vegetable matter, which are famous for this property.

Iron.—Another constituent of soils is iron.

It always is present, though not in the form of metallic iron, but
in the state or condition of an oxyd of iron. When metallic iron
is exposed to air and moisture, it becomes rough, and covered
with reddish or brown scales. This is what is called, in common
language, rust of iron, the process is called rusting. In Chemical
language, it is called the oxydation of iron, and the product an oxyd
of iron. There are three oxyds of Iron; when in soils, it is gen-
erally in the condition of peroxyd, or its highest degree of ox-
ydation, and gives a reddish or brown color to them. It is this
which gives our red and yellow clay soils their peculiar color, and
frequently also tinges sand—which, thus colored, is called Ferru-
ginous sand. It has several important uses in the soil.

First.—It is one of the necessary constituents of the human
body, being always found in the blood of healthy persons. From
the impossibility of its existence in the air, we know that the body
must be supplied with it from the food which it consumes; but the
plants used for food, can no more obtain it from the air, than ani-
mals can, hence they must obtain it from the soil, and it is there-
fore a necessary constituent of soils.

Not only is it itself food for plants, but it is a gatherer of food
for them from the atmosphere.

Baron Liebig, one of the ablest writers on Agricultural Chemis-
try, of this or any other day, though overlooking the first use of
iron in a soil, so clearly and satisfactorily explains the second, that
I cannot do better than use his own words :

* "Peroxyd of iron and alumina," says this able and eloquent
writer, "are distinguished from all other metallic oxyds,) i. e.
rusts of metals,) by their power of forming solid compounds with

* Chemistry, in its Application to Agriculture and Physiology. (Edited by
Lyon Playfair and Dr. Gregory, 4th London Edition.