he increased
use of potash has been due largely to the propaganda of the German sales
agents. An examination of a map showing distribution of the use of
fertilizers over the country indicates very clearly the erratic
distribution of the effects of these various activities. One locality
may use large amounts, while adjacent territory of similar physical
conditions uses little. The sudden withdrawal of fertilizers for a
period of three or four years during the war had very deleterious
effects in some localities, but was not so disastrous as expected in
others,--emphasizing the fact that the use of fertilizers has been
partly fortuitous and not nicely adjusted to specific needs.

[Illustration: FIG. 4. FERTILIZER SITUATION IN THE UNITED
STATES. SMITHSONIAN INSTITUTION--UNITED STATES NATIONAL MUSEUM]

NITRATES

ECONOMIC FEATURES

There are several sources of nitrogen for fertilizer purposes: mineral
nitrates, nitrogen taken from the air by certain plants with the aid of
bacteria and plowed into the soil, nitrogen taken directly from the air
by combining nitrogen and oxygen atoms in an electric arc, or by
combining nitrogen and hydrogen to form ammonia, nitrogen taken from the
air to make a compound of calcium, carbon, and nitrogen (cyanamid),
nitrogen saved from coal in the form of ammonia as a by-product of
coke-manufacture, and nitrogen from various organic wastes. Nitrogen in
the form of ammonia is also one of the potential products of oil-shales
(p. 150). While the principal use of nitrogenous materials is as
fertilizers, additional important quantities are used in ammonia for
refrigerating plants, and in the form of nitric acid in a large number
of chemical industries. During the war the use of nitrates was largely
diverted to explosives manufacture. The geologist is interested
principally in the mineral nitrates as a mineral resource, but the other
sources of nitrogen, particularly its recovery from coal, also touch his
field.

Almost the single source of mineral nitrates for the world at present is
Chile, where there are deposits of sodium nitrate or Chile saltpeter,
containing minor amounts of potassium nitrate. About two-thirds of the
Chilean material normally goes to Europe and about one-fourth to the
United States. The supply has been commercially controlled chiefly by
Great Britain and by Chilean companies backed by British and German
capital.

The dependence of the world on Chile became painfully ap