a time, with iron shovels, allowing sufficient time between each
filling, for melting down the various charges, until the pot is entirely
filled with fused Glass. By this method, every pot in the furnace is fully
charged with liquid metal, in about twelve to fifteen hours; air-bubbles
and striæ then abound, and they are not expelled until thirty to
forty hours more have elapsed, during which period—viz., from fifty
to sixty hours, the gas and air-bubbles are driven off, and the mass
becomes homogeneous. English melting-pots, being usually much larger
than the French, require a longer period for fusion, thus increasing
the difficulty, if a second filling be required during the week; but the
Glass is not usually so pure as the first, through less time being allowed
for the second fusion. When all the pots are filled, and the mouths are
securely stoppered and clayed up, the founding commences, during which
thirty to forty hours (as before alluded to) the furnace is urged to its
utmost intensity; no pyrometer is used, as the heat varies according to
the condition of the furnace, aspect, and intensity of the wind, quality
of the fuel, and attention and tact of the
tiseur, attendant, or stoker.
Nevertheless, there are certain signs by which a practised
eye can detect the fitness or unfitness of the metal for working: these
are—the whiteness of the flame exuding from the furnace, on each
side of the pot; also by occasionally withdrawing, with an iron rod,
a little of the melted Glass from the top of the metal, through a small
sight-hole in the stopper, and at fixed times taking proofs of the metal.
Saturday and Sunday are the days when the furnace requires the greatest
heat, so that the working may be commenced early on Monday morning.
