de materials in making very low-priced fertilizers.

A legitimate use of filler is to give good physical condition to a
fertilizer. Some materials, such as nitrate of soda and muriate of
potash, take up moisture and then become hard. The addition of peat or
limestone or other absorbent is necessary to keep the mass in condition
for drilling. The use of some steamed animal bone or high-grade tankage
in the mixture helps to prevent caking. The home-mixer can use a drier
without loss, as he does not pay freight upon it. Dry road dust will
serve his purpose. His need of a drier may be greater than that of the
manufacturer, as he probably will use only high-grade unmixed
materials. If the use of the home-mixture is immediate, no drier to
prevent caking is needed, but its presence facilitates drilling.
Storage of unmixed materials in a dry place is an aid in maintaining
good condition.

Ingredients in the Mixture.--The matters of interest to the farmer are
the determination of the amounts of nitrogen, phosphoric acid, and
potash that he should apply to a particular field, their availability,
and their cost. Let us assume that he has found 300 pounds of a
fertilizer containing 3 per cent nitrogen, 10 per cent phosphoric acid,
and 6 per cent potash to be an excellent application for wheat on a
thin soil that is to be seeded to clover and timothy. This fertilizer
contains 3 pounds of nitrogen to each 100 pounds. He applies 300 pounds
of the fertilizer per acre, or 9 pounds of nitrogen. The fertilizer
contains 10 pounds of phosphoric acid to the 100 pounds. He thus
applies 30 pounds of phosphoric acid per acre. The fertilizer contains
6 pounds of potash per 100 pounds, and he therefore applies 18 pounds
per acre. What he has really learned, then, is that an acre of this
land, when seeded to wheat, needs 9 pounds of nitrogen, 30 pounds of
phosphoric acid, and 18 pounds of potash. It is in these terms he
should do his thinking, and the matter of fertilization becomes simple.

In the general farming of the Pennsylvania experiment station, it is
the practice to depend upon nitrate of soda as the source of a
fertilizer for wheat. Manufacturers claim that sulphate of ammonia and
tankage would be better. The farmer soon will learn what he prefers for
his soil, provided he practices home-mixing.

Let us assume that he uses nitrate of soda, which never varies much
from 15 per cent in its content of nitrogen. If 100 pounds of nitrate
c