The modern
injector burner exhibits the same phenomenon of dilution, and is to the
same extent efficacious in preventing polymerisation; but inasmuch as it
permits a larger proportion of air to be introduced, and as the addition
is made roughly half-way along the burner passage, the cold air is more
effectual in keeping the former part of the tip cool, and in jacketing
the acetylene during its travel through the latter part, the bore of
which is larger than it otherwise would be.
INJECTOR AND TWIN-FLAME BURNERS.--In practice it is neither possible to
cool an acetylene burner systematically, nor is it desirable to construct
it of such a large mass of some good heat conductor that its temperature
always remains below the dissociation point of the gas. The earliest
direct attempts to keep the burner cool were directed to an avoidance of
contact between the flame of the burning acetylene and the body of the
jet, this being effected by causing the current of acetylene to inject a
small proportion of air through lateral apertures in the burner below the
point of ignition. Such air naturally carries along with it some of the
heat which, in spite of all precautions, still reaches the burner; but it
also apparently forms a temporary annular jacket round the stream of gas,
preventing it from catching fire until it has arrived at an appreciable
distance from the jet.
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