or compound Glass, manufactured at the Falcon Works, (of a beautiful
topaz tint, coloured by uranium, which became richer in hue by diminishing
the usual proportion of lead, and by increasing the alkali,) fractured
three months after it was cut. Complaints from purchasers at home and
abroad reached the Works, and the whole had to be replaced at the expense
of the manufacturer.
Excess of alkali causes continual exudation;
the cementing property escapes, entire fracture is the result, and
no remedy can check the evil. A piece of ancient light blue Glass,
since it came into the possession the British Museum, has spontaneously
fractured, and some parts almost to pulverization; an effect caused by
its excess of impurity of alkali.
Formerly, lears were heated by the waste
caloric of the furnace; they were elevated about six feet or more from
the floor of the Glass-house, to catch the flame and warmth from the
top of the furnace flues. This contrivance saved the entire lear fuel;
but from the inconvenience and breakage caused by the Glass being taken
up steps, and the impossibility of regulating the heat and smoke, it
has been long since dis-used in England. Modern lears are placed a few
feet above the floors of the Glass-house, as already described: they not
only anneal the Glass better, but the saving of breakage, in comparison
with the old system, is found to be considerable, and wholly covers the
expense of separate fuel. The amount of breakage in the lears varies
considerably; the minimum average may be taken at 2 per cent. upon the
manufacture; under unfortunate or bad
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