Gaud has shown
that when pure acetylene is burnt at the normal rate in 1-foot Bray jets,
growths of carbon soon appear, but do not obstruct the orifices during
100 hours' use; if, however, the gas-supply is checked till the flame
becomes thick, the growths appear more quickly, and become obstructive
after some 60 hours' burning. On the assumption that acetylene begins to
polymerise at a temperature of 100 deg. C., Gaud calculates that
polymerisation cannot cause blocking of the burners unless the speed of
the passing gas is so far reduced that the burner is only delivering one-
sixth of its proper volume. But during 1902 Javal demonstrated that on
heating in a gas-flame one arm of a twin, non-injector burner which had
been and still was behaving quite satisfactorily with highly purified
acetylene, growths were formed at the jet of that arm almost
instantaneously. There is thus little doubt that the principal cause of
this phenomenon is the partial dissociation of the acetylene (i.e.,
decomposition into its elements) as it passes through the burner itself;
and the extent of such dissociation will depend, not at all upon the
purity of the gas, but upon the temperature of the burner, upon the
readiness with which the heat of the burner is communicated to the gas,
and upon the speed at which the acetylene travels through the burner.
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