When the forests that supplied wood charcoal
were almost used up, iron and steel grew still dearer and scarcer.
Could coal dug up from the earth be used instead of wood charcoal for
smelting iron and making steel? It did not seem so. Gases are driven
off from coal when it is burned. These gases ruin iron and steel.
Then someone had a wonderful idea. Charcoal is made by roasting wood in airtight ovens. Why not try roasting coal in airtight ovens also? Perhaps the roasted coal would be used instead of charcoal for smelting iron and making steel.
"Cooked" coal or "coke" was made. It was tried first in the smelting of iron and later in the manufacture of steel. It took time to find out how to use coke for these purposes, but finally it was a great success.
Now for the first time it was possible to make iron and steel cheaply and in great quantities. Now it was possible to make iron and steel machines, too-- and even to make them in great numbers. Inventors began to invent hundreds and hundreds of machines. Thus the Machine Age began when men began to understand how to use coal to make iron and steel!
Roasting the coal to make coke drives off the substances in the coal that spoil iron and steel. Some of these wastes are driven off in the form of gases, others in the form of gummy coal-tar liquids. Getting rid of these wastes used to be a great nuisance. The gases escaped into the air and killed the grass and trees and flowers. The coal tar ran off into the streams and poisoned the fish.