rocks!

To return to the smelting process. The last product--the regulus--is
again calcined, with the view of bringing the iron to the state of an
oxide. It is again melted, slagged, and run into pigs. In this last
operation, the whole iron is driven out in the slag, and the
remainder--'white metal,' as it is called--is almost a pure sulphuret
of copper. The sulphur, having all along preserved its combination
with the copper--a fine illustration of the theory of chemical
attraction--must now at length be expelled. This is effected by the
last process of roasting. When in a state of fusion in the furnace,
the charge is exposed to a stream of air, in which case a double
action ensues. Part of the oxygen enters into combination with the
sulphur, producing sulphurous acid, which is expelled in the form of
vapour, and part of it combines with the copper remaining in the
furnace; this is again run out into the form of pigs, and in this
state it is termed 'blistered copper.' To produce the finer kind of
copper, another process has yet to be gone through; but for ordinary
_tough copper_, it is at once transferred to what we may describe as
the last stage, and that is--

3. _Refining._--We quote Mr Vivian:--'The pigs from the roasters are
filled into the furnace through a large door in the side: the heat is
at first moderate, so as to complete the roasting or oxidising
process; after the charge is run down, and there is a good heat on the
furnace, the front door is taken down, and the slags skimmed off. An
assay is then taken out by the refiner with a small ladle, and broken
in the vice; and from the general appearance of the metal in and out
of the furnace, the state of the fire, &c., he judges whether the
toughening process may be proceeded with, and can form some opinion as
to the quantity of _poles_ and charcoal that will be required to
render it malleable, or, as it is termed, to bring it to the _proper
pitch_. The copper in this state is what is termed _dry_: it is
brittle, of a deep-red colour, inclining to purple, an open grain, and
crystalline structure. In the process of toughening, the surface of
the metal in the furnace is first well covered with charcoal; a pole,
commonly of birch, is then held into the liquid metal, which causes
considerable ebullition, owing to the evolution of gaseous matter; and
this operation of _poling_ is continued, until, from the assays which
the refiner from time to time takes, he percei