annually "sold or used by producer" in the United States in million long
tons (2,240 lbs.)
1880 0.2
1890 0.5
1900 1.5
1910 2.655
1920 4.104
1930 3.926
1940 4.003
1945 5.807
1950 11.114
1955 12.265
1955 (world: about 56)
1960 17.202
1962 19.060
Sources: U.S. Bureau of the Census. _Historical Statistics of the United
States 1789-1945_ (1949); _Statistical Abstract of the United States._