ii 2? ii 2? 2? 2? 2? 2? 2? 2? 2? 9? 2? 2? 2? 2? 92 2? 92 2? 2? 22.9? 2? ~
2? 2222 2? 2? 2?
392
MINERALS YEARBOOK

LIQUIDATION OF MINE CAPACITY

 Trend of capacity, 1890—1931.—The depression of general business
has continued the liquidation of mine capacity which has been going on in
the bituminous industry ever since 1923. Figure 18 shows the capacity of
the mines active in each year. The curve of "full-time capacity" represents
what the mines in operation could do with the equipment and labor actually
employed if they produced for 308 days at the same rate they actually did
produce on the days they were operating. Coal is loaded on 308 days or more,
and many individual mines work as much as 308 days. However, it is not feasible
for all

U)

z

Iz

z

0

FIGURE 18.—Trend of bituminous-coal production and of mine capacity
in the United States, 1899—1932.

mines to attain so high a figure because of unavoidable losses of time through
breakdowns, falls of roof, failure of power supply, and the seasonal character
of the market. For these reasons the more conservative figure of 280-day
capacity is also shown, a figure suggested some years ago by th~e coal committee
of the American Institute of Mining and Metallurgical Engineers.
 Capacity was increasing rapidly in the period up to the World War. Expansion
was greatly stimulated by the high prices of 1916 to early 1923. Thousands
of new mines were opened, and the growth was especially rapid just after
the war when additional labor was readily obtainable at the high wages then
prevailing. The peak was reached in 1923, when the mines in operation had
an annual capacity at 308 days of 970,000,000 tons. So great an excess above
the needs of the