if igneous
emanations contain free oxygen and sulphur, or sulphur dioxide, it would
be expected that as they become cool sulphur trioxide would be formed
which would result in the sulphate at suitable temperature.[36]

Other deposits containing gold are discussed in connection with silver
on following pages.

SILVER ORES

ECONOMIC FEATURES

Silver has two important uses--in money and in the arts. As money, it is
used in the United States and Europe for subsidiary coinage,--silver
coins normally circulating at more than their intrinsic value,--but its
greatest monetary use is in India and China, where it has been the basis
for the settlement of foreign exchange balances. In China also it is the
money standard of the country. In the arts, silver is employed chiefly
in the making of articles of luxury, such as jewelry and tableware. In
the Orient this use is closely related to its use as money, since the
natives invest their savings both in silver jewelry and silver coins.
There is some consumption of silver by certain chemical industries, and
quantities of increasing importance are used in the form of silver salts
by the photographic and moving picture industries. It has been estimated
that before 1914 about two-thirds of the new silver produced went into
the arts and one-third into money. During the war, however, increasing
amounts were used in coinage, and less than one-fifth of the output was
used in the arts. Demands for silver for monetary purposes will probably
continue to take the larger part of the world's production for some
time. In this connection it may be noted that India has adopted a gold
standard, but that the conservative habits of the population will
doubtless continue to call for large amounts of silver.

About half of the silver production of the world comes from the dry or
siliceous silver ores, which are mined solely for that metal and the
associated gold; and about half of the production is obtained as a
by-product in the mining of other metals, principally copper and lead.
The average grades of these ores, in combined values of gold and silver,
were referred to on p. 228. While the aggregate amount of silver
obtained as a by-product of other ores is large, the percentage of
silver in the copper or lead in any mine is ordinarily very small.
Consequently the world output of silver depends to a considerable extent
upon conditions in the copper- and lead-mining industries.

Of the total wor