na. Still others note the frequent presence of nitrogen in
volcanic exhalations and the association of the Chilean nitrate beds
with surface volcanic rocks; they suggest that these rocks were the
source of the nitrogen, which under unusual climatic conditions was
leached out and then deposited by evaporation.

PHOSPHATES

ECONOMIC FEATURES

The principal use of natural phosphates is in the manufacture of
fertilizers. They are also used in the manufacture of phosphorus,
phosphoric acid, and other phosphorus compounds, for matches, for
certain metallurgical operations, and for gases used in military
operations.

The material mined is mainly a phosphate of lime (tricalcium phosphate).
To make it available for plant use, it is treated with sulphuric acid to
form a soluble superphosphate; hence the importance of sulphuric acid,
and its mineral sources pyrite and sulphur, in the fertilizer industry.
A small percentage of the phosphate is also ground up and applied
directly to the soil in the raw form. Other phosphatic materials are the
basic slag from phosphatic iron ores made into Thomas-process steel,
guano from the Pacific islands, and bone and refuse (tankage) from the
cattle raising and packing countries. These materials are used for the
same purposes as the natural phosphates.

The United States is the largest factor in the world's phosphate
industry, with reference both to production and reserves.

The largest and most available of the European sources are in Tunis and
Algeria, under French control, and in Egypt, under English control.
Belgium and northern France have been considerable producers of
phosphates, but, with the development of higher grade deposits in other
countries, their production has fallen to a very small fraction of the
world's total. There also has been very small and insignificant
production in Spain and Great Britain. Russia has large reserves which
are practically unmined.

While there is comparatively little phosphate rock in western Europe, a
considerable amount of the phosphate supply is obtained as a by-product
from Thomas slag, derived from phosphatic iron ores. These ores are
chiefly from Lorraine and Sweden, but English and Russian ores can be
similarly used.

Outside of Europe and the United States, there are smaller phosphate
supplies in Canada, the Dutch West Indies, Venezuela, Chile, South
Australia, New Zealand, and several islands of the Indian and South
Pacific Oceans