80
completion of the rail network by 1900, and the subsequent
decline in the amount of steel devoted to that end. One
might speculate about future needs for additional numbers
of automobiles, bridges, and buildings. To the extent
that production of these or other like items is increased,
the subsequent demand for steel and iron may be increased
as well. The same holds true for copper and its various
applications. In brief, the rate of metals demand for
any given year is tied to the needs of metals using
industries and modified by changes in markets, complexity
of product, and by materials substitution.
It is difficult to foretell just what the demand
for metals will be in the future but several of the
factors mentioned above tend to indicate that the ratio
of metals extraction to national product will continue to-
decline. Increased complexity of products, substitution
of other materials, and productive activity devoted to
non-metals using endeavors would lessen the rate of
increase in metals demand. But, while the rate of growth
in annual metals consumption has been less than that of
output as a whole, the annual demand for metals has not
stabilized; on the contrary, the amount of metals in use
50
has in fact continued to increase at an increasing rate.
^See Appendix B.4 for information related to
rates of increase in metals consumption and metals in
use.