This, until recently, has
required the use either of a rather complicated furnace, or a blast of
air under pressure, to increase the rapidity of combustion. Since the
conclusion of my experiments on the theoretical construction of burners,
I have found that the high-power burners, previously described, are
capable of heating a crucible equal in size to their own diameter
to bright redness without the assistance of a chimney, provided the
crucible is protected from draughts by a fireclay cylinder.
This is an important point, as it renders the production of a continuous
bright red heat a matter of the greatest ease, even in crucibles of a
comparatively large size. Where the heat is steady, and certain not to
rise above a definite point, it can safely be used for such purposes as
hardening penknife blades and other articles which are very irregular
in thickness, the thin edges not being liable to be burnt or damaged by
overheating.
For the highest temperatures air under pressure is a necessity, as we
require a large quantity of gas burnt in as small a space as possible
with the maximum speed, and given this air supply, we are very little
hampered by conditions, as an explosive mixture may be blown through a
gauze into a fireclay chamber, closed, except so far as is necessary to
allow the escape or burnt gases.
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