In
deep-shaft mines, coal is carried to the surface by cages hoisted through
the shaft. It is sorted and cleaned above ground.
One of the largest uses of coal is found in the factories where numerous
articles of iron and steel are made. The world of industry depends so much
upon iron that it is called the metal of civilization.
[Illustration: Iron Smelters.]
The iron and coal industries are closely related, for coal is used to make
iron into steel. If you stay in Pennsylvania you may catch a glimpse of
the process by which iron is made usable.
As it comes from the mine it is not pure, but is mixed with ore from which
it must be separated. In the regions of iron-mines you will see towering
aloft here and there huge chimneys, or blast-furnaces, at times sending
forth great clouds of black smoke and at times lighting the sky with the
lurid glow of flames. In these big blast-furnaces, the iron ore and coal
are piled in layers. Then a very hot fire is made, so hot that the iron
melts and runs down into moulds of sand, where it is collected. This
process is called smelting.
The iron thus obtained, though pure, is not hard enough for most purposes.
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