d as a pigment, or paint. Red lead, an oxide, is a
pigment; litharge, also an oxide, is used for glazing the cheaper kinds
of pottery. About two hundred and thirty thousand tons of lead are
produced in the United States and one-half as much is imported--mainly
from Mexico and Canada. The linotype machines, now used in all large
printing establishments, have increased the demand for lead.

=Other Metals.=--Most of the remaining economic metals occur in small
quantities as compared with iron, copper, gold, and silver. Some of
them, however, are highly important from the fact that in various
industrial processes no substitutes for them are known.

_Quicksilver_, or _mercury_, is the only industrial metal that at
ordinary temperatures is a liquid. It is the base of the substance
calomel, a chloride, and corrosive sublimate, a dichloride, both of
which are employed as medicines. It is essential in the manufacture of
thermometers and barometers, but is used chiefly, however, as a solvent
of gold, which it separates from the finely powdered ore by solution or
amalgamation. Quicksilver occurs in the mineral cinnabar, a sulphide.

Nearly one-half the world's product comes from California. The New
Almaden mines of Santa Clara County produce over five thousand flasks
(each seventy-six and one-half pounds net); those of Napa County nearly
nine thousand flasks; the mines of the whole State yield about
twenty-six thousand flasks, valued at $1,200,000. Almaden, Spain, and
Idria, Austria, produce nearly all the rest of the output. An average of
about fifteen thousand flasks are exported from San Francisco, mainly to
the mines of Mexico, and Central and South America.

_Tin_ is about the only metal of industrial value whose ores are not
found in paying quantities in the United States. Small quantities occur
in San Bernardino County, Cal., and in the vicinity of Bering Strait,
Alaska, but it is doubtful if either will ever pay for development.
About three-fifths of the world's product comes from the Straits
Settlements on the Malay Peninsula; the nearby islands of Banca and
Billiton also yield a considerable quantity.

The mines of Cornwall, England, have been worked for two thousand years
and were probably the source of the tin that made the "bronze age." The
United States imports yearly about twenty million dollars worth of tin,
about half of which comes from the Straits Settlements. This is used
almost wholly for the manufacture o