192

 To obtain annual rates of growth in metals in use

for 1920-1960, the basic data were modified to take

increases in apparent consumption for the period 1860-1900

into account. Since no equivalent Bureau of Mines data

exist for 1860-1900, changes in iron and copper production

for the period were used to obtain an approximate figure

for total metals added.

 Copper production for 1861-1900 was approximately

50 percent of total copper production for 1900-1920.

Therefore, the figure for copper in use in 1920 was

increased by 50 percent and the figure for 1960 by the

same absolute amount. Exports for 1861-1900 and 1900-1920

were assumed to be the same percentage of total production

for both periods. Pig iron shipments for the period 1860-

1900 were approximately 36 percent of shipments for 1900-

1920. Therefore, the figure for iron in use in 1920 was

increased by 36 percent and the figure for 1960 increased

by the same absolute amount. As with copper, exports

were assumed to be the same for both 1860-1900 and

1900-1920. The amounts by which 1920 and 1960 copper

and iron figures were increased represents an estimate

of copper and iron in use in 1900.

 Absolute quantities are overstated to the degree

that metals have been lost from the stock of metals in

use. However, if the percent lost per year were