Since any flame supplied with too little air tends to emit
free carbon or soot, it follows that any well-made acetylene burner
delivering a gas containing benzene vapour will yield a more or lens
smoky flame according to the proportion of benzene in the acetylene.
Moreover, at ordinary temperatures benzene is a liquid, for it boils at
81 deg. C., and although, as was explained above in the case of water, it is
capable of remaining in the state of vapour far below its boiling-point
so long as it is suspended in a sufficiency of some permanent gas like
acetylene, if the proportion of vapour in the gas at any given
temperature exceeds a certain amount the excess will be precipitated in
the liquid form; while as the temperature falls the proportion of vapour
which can be retained in a given volume of gas also diminishes to a
noteworthy extent. Should any liquid, be it water or benzene, or any
other substance, separate from the acetylene under the influence of cold
while the gas is passing through pipes, the liquid will run downwards to
the lowest points in those pipes; and unless due precautions are taken,
by the insertion of draw-off cocks, collecting wells, or the like, to
withdraw the deposited water or other liquid, it will accumulate in all
bends, angles, and dips till the pipes are partly or completely sealed
against the passage of gas, and the lights will either "jump" or be
extinguished altogether.
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