wood. The wood is kindled, and by the time it has burned
out, the sulphur in the ore has begun to burn, and in a good-sized
heap it will continue to burn for perhaps two months.

Such a heap is a good thing to keep away from, for the fumes of
sulphur are very disagreeable. Indeed, they will kill trees and other
growing things wherever the wind may carry them, even several miles
away. The managers of mines of copper as well as of gold and silver
have learned to economize; and it has been found that instead of
letting these fumes go into the air, they may be made to pass through
acid chambers lined with zinc and full of water. The water holds the
fumes, and can be used in making sulphuric acid.

After the ore has been roasted, it is put into the furnace for
smelting. If you should make an oven and put into it a mixture of wood
and roasted copper, that would be a smelting furnace. Set the wood on
fire, pump in air to make the flame hot, and if your furnace could be
made hot enough,--that is, 2300 deg. F., or about eleven times as hot as
boiling water,--you could smelt copper. Of course the furnace of a
real smelting factory will hold tons and tons of copper ore and has
all sorts of improvements, but after all it is in principle only an
oven with wood and ore and draft. Another sort of furnace, which is
better for some kinds of ore, has a grate for the fire and a bed above
it for the copper.

Imagine an enormous furnace holding between two and three hundred tons
of metal and burning with such a terrific heat that by contrast
boiling water would seem cool and comfortable. Suddenly, while you
stand looking at it, but a long way off, a door flies open and the
most beautiful cascade--only it is not a waterfall, but a _copper_
fall--pours out. It looks like red, red gold, rich and wonderful, with
little flames of red and blue dancing over it. It might almost be one
of the fire-breathing dragons of the old story-books; and if it should
get loose, it would devour whomever it touched far quicker than any
dragon. It hardly seems as if any one could manage such a monster; but
it looks easy, after you have seen it done. An enormous horizontal
wheel revolves slowly. On its edge are moulds shaped like bricks, but
much larger. On the hub of the wheel a workman sits to direct the
filling of these. A set of them is filled, and moves on, and others
take their place. When they are partly cooled, another workman, at the
farther side of th