All metals are got from the earth where they exist in the form
of “ores” (in reality metals combined with other matters), and
“smelting” is the process of getting rid of these other matters,
the chief of which are sulphur and oxygen. The ores when dug from
the mine are generally stamped into powder, then “roasted,” that is,
made hot and kept so for some time to drive off water, sulphur, or
arsenic, which would prevent the “fluxes” acting properly. The fluxes
are substances which will mix with, melt, and separate the matters to
be got rid of, the chief being charcoal, coke, and limestone. The ore
is then mixed with the flux and the whole raised to a great heat; as
the metal is separated it melts, runs to the bottom of the “smelting
furnace” and is drawn off into moulds made of sand; it is thus
cast into short thick bars called “pigs,” so we hear of pig-iron,
pig-lead, &c. Iron is smelted from “ironstone,” which is mixed with
coke and limestone. The heat required to smelt iron is so very great,
that a steam-engine is now always employed to blow the furnace
(before the invention of the steam-engine, water-mills were used
for the same purpose). The smelting is conducted in what is called a
blast furnace. When the metal has all been “reduced” or smelted, and
run down to the bottom of the furnace, a hole is made, out of which
it runs into the moulds; this is called “tapping the furnace.”
Smelting is often confounded with melting, as the names are somewhat
alike, but the processes are entirely different; in melting, the
metal is simply liquified, in smelting the metal has to be produced
from ores which often have no appearance of containing any, as in the
case of iron-stone, which looks like brown clay. By way of experiment
let the reader take a small portion of “litharge,” which is a reddish
powder, mix it with a drop of oil into a thick paste and place it on
the end of a flat piece of charcoal or wood, and direct the flame of
a candle upon it by means of a blow-pipe; a slight hissing noise will
be heard, and in a moment or two a small, bright globule of lead will
make its appearance.