Elevation of the furnaces, and interior view of the Glass-house
and working operations.
FURNACES.
A flint Glass furnace, in principle, is
intermediate between an air furnace and an oven; too much draught would
drive the caloric up the chimney or shaft, and too little would fail
to yield sufficient oxygen to support the requisite heat. The draught
must never be too strong to prevent a plus, or pressure of short and
sharp flame outwards from the bye-holes of the furnace on each side of
the pot mouths. Large caves,
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