Three methods of overcoming this defect have been used:
in one the arms are constructed entirely of steatite, in another they are
made of such soft metal as easily to be bent back again into position
with the fingers or pliers, in the third each arm is in two portions,
screwing the one into the other. The second type is represented by the
original Phos burner, in which the curved arms of B are replaced by a
pair of straight divergent arms of thin, soft tubing, joined to a pair of
convergent wider tubes carrying the two tips. The third type is met with
in the Drake burner, where the divergent arms are wide and have an
internal thread into which screws an external thread cut upon lateral
prolongations of the convergent tubes. Thus both the Phos and the Drake
burner exhibit a pair of exposed elbows between the gas inlet and the two
tips; and these elbows are utilised to carry a screwed wire fastened to
an external milled head by means of which any deposit of carbon in the
burner tubes can be pushed out. The present pattern of the Phos burner is
shown in Fig. 9, in which _A_ is the burner tip, _B_ the wire
or needle, and _C_ the milled head by which the wire is screwed in
and out of the burner tube.
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