but after the ore becomes so much heated that the sulphur
in it begins to burn, no further artificial aid is necessary. Little
by little the ore is added in quantities sufficient to keep the
fire going. The object of the roasting is to drive off as much
sulphur as possible.

After being raked from the roasting furnace, the ore is wheeled
in barrows to the huge upright furnaces and is thrown in. Here
such materials as limestone and iron are also added to aid in the
formation of a perfectly fused or molten mass. These substances
are known as fluxes. With the melting of the ore the copper begins
to separate from the impurities.

The melted ore, in the form of a glowing liquid, gathers at the
bottom of the furnace and runs out into a large kettle-like receptacle.
When ore of these vessels is full it is tipped up and the molten
copper which has collected at the bottom, because it is heavier than
the slag, is allowed to run into another large kettle, supported
by chains from a rolling truck above.

[Illustration: FIG. 107.--SHIPPING COPPER MATTE]

The slag is dumped into a car and is carried outside, while the huge
dish containing the copper and some slag is swung to the opposite
side of the building, where its contents are cast into another
furnace. A very strong blast of air is forced up through the molten
mass in this furnace, and the remaining portion of slag is blown
out at the top in a shower of glowing particles.

From the bottom of the furnace the liquid copper is drawn out and
allowed to run into moulds where it finally cools. It is then known
as copper matte. The copper still contains some impurities, and
retains in addition whatever gold and silver may have been present
in the ore. Most copper ores carry a small amount of these precious
metals.

The heavy bars of copper matte are now ready for shipment to some
manufacturing point, where they are refined still further and made
into the various copper utensils, copper wire, etc. Copper is valuable
for many purposes, as it does not rust easily, is highly malleable
and ductile, and is a good conductor of electricity.

In the great copper-mines upon Lake Superior, copper is found in the
native state mixed with the rock, and does not have to be smelted;
but in most mines the ore must go through a process very like the
one described before metallic copper can be obtained.

It does not matter how remote a region may be, how intense the
heat or cold, or how deser