.

The lumps of copper, such as those which delighted the hearts of the
Indians, are known to-day as "barrel" copper, because they are of a
good size to be dropped into barrels and carried away for smelting.
The great boulders which the Indians could not use are called "mass"
copper. Sometimes they weigh as much as five hundred tons. The copper
in them is almost pure, and a big boulder is worth perhaps $200,000.
Nevertheless, the mine-owners do not rejoice when they come upon such
a mass in their digging, for it cannot be either dug or blasted, and
has to be cut away with chisels of chilled steel. Now, a mine may be
wonderfully rich in metal, but if working it costs too much, then
another mine with less metal but more easily worked will pay better.
So it is with these great masses of copper. They are interesting to
study and they look well in museums, but they do not pay so well as
the "stamp" copper which is found in humble little bits in the gangue,
or the rock of the vein, and has to be pounded in a stamp mill. This
gangue is dug out and broken up as in mines of other metals. The
copper is much heavier than the rock, so it is easy to get rid of the
worthless gangue by means of a flow of water. The gangue of the
Michigan mines is exceedingly hard, but the stamps are so powerful
that one can crush five hundred tons in less than twenty-four hours.
Some copper can be taken out of the mortars at once, but the rest of
the broken gangue is fed to jigs, or screens, which are kept under
jets of water. The water is thrown up from below and the lighter rock
is tossed away, while the heavier copper falls through the tiny holes
in the screens.

[Illustration: IN A COPPER SMELTER

The men are pouring hot copper into moulds for castings.]

After the ore has been through all these experiences, it comes out
looking like dark-colored sand or coarse brown sugar. It is not
interesting, and no one who saw it for the first time would ever fancy
that it was going to turn into something beautiful. It is dumped into
freight cars and trundled off to the smelting furnaces. But however
uninteresting it looks, it is well worth while to follow these cars to
see what happens to it at the smelters. First of all, even before it
goes into the smelting furnace, it must be roasted. There is usually
sulphur combined with the copper, and roasting will get rid of much of
it. In some places this is done by building up a great heap of ore
with a little