weeks steady firing up to get a heat we can work with."
"Three weeks!" exclaimed Lawrence,
astonished. "Then it would hardly pay to let the fire go down
for the clinkers?"
"As for them, we just slip the grate to
one side, and cut 'em off from the sides of the eye with an
instrument we drive up from below. We never let the fire go
down till the furnace burns out. The furnace is built inside
the cone."
"And where do you melt your glass?"
"In pots set into the furnace, just
overhead here, as I will show you by and by. Our glass pots
are closed in, so that no impurities from the fire can get into
them. That 's the way pots have to be arranged, where flint
glass is made. But in furnaces where they make common green
glass, which they are not so particular about, the pots are left
open at the top, for the advantage of getting the direct action
of the heat on the melting materials. That lets the flux run
into the fire sometimes, and that spoils the furnace; so that
green-glass furnaces have to shut down about once every year."
Just then a being who seemed (to the
imagination of the lad, at least,-- the Doctor had forgotten his
Arabian Nights some years since),-- a being who seemed the dark
genie of the place, advanced from some dismal recess in which he
had lain concealed, and thrust a ponderous iron spear, or lance,
through the bars, directly into the eye of Lawrence's dragon,
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