In addition to furnishing copper to domestic

industries, by 1900 the United States had become engaged

in a booming export trade in copper with almost half of

domestic production being sent abroad for use in the

rapidly expanding electrical industries of other
 27
countries.27 During the early 1900s, the United States

continued to do a lively copper export business as

domestic production, continuing to increase at a brisk

pace, was supplemented by imports of ores and concen-

trates for refining and reshipment abroad. In 1920,

for example, net imports of copper ores and concen-

trates by copper content amounted to 150,808 short tons

and refined copper exports to 221,241 short tons, the

excess reflecting the added product of American mines.

In 1925 refined net exports of copper amounted to

434,146 short tons compared to net imports of ore and

concentrates of 263,228 short tons, but the era of the

United States as a net exporter of copper was drawing

to a close. By 1929 imports of ores and concentrates

exceeded refined net exports by only 28,281 short tons,

and imports of copper ore by copper content remained

fairly equal to refined exports from then until the

eve of the Second World War.28

 27Twelfth Census, Manufactures, Part I, p. Ivii.
 Figures for copper production are shown in Appendix B.

 28Historical Statistics, p. 368, Series 225-30.