Acetylene requires 2.5 volumes of oxygen to burn it completely; but in
the construction of an acetylene-oxygen blowpipe the proportion of oxygen
is kept below this figure, viz., at 1.1 to 1.8 volumes, so that the
deficiency is left to be made up from the surrounding air. Thus at the
jet of the blowpipe the acetylene dissociates and its carbon is oxidised,
at first no doubt to carbon monoxide only, but afterwards to carbon
dioxide; and round the flame of the gaseous carbon is a comparatively
cool, though absolutely very hot jacket of hydrogen burning to water
vapour in a mixture of oxygen and air, which protects the inner zone from
loss of heat. As just explained, theoretical grounds support the
conclusions at which Fouche has arrived, viz., that the temperature of
the acetylene-oxygen blowpipe flame is above that at which hydrogen will
combine with oxygen to form water, and that it can only be exceeded by
those found in a powerful electric furnace. As the hydrogen dissociated
from the acetylene remains temporarily in the free state, the flame of
the acetylene blowpipe, possesses strong reducing powers; and this,
coupled probably with an intensity of heat which is practically otherwise
unattainable, except by the aid of a high-tension electric current,
should make the acetylene-oxygen blowpipe a most useful piece of
apparatus for a large variety of metallurgical, chemical, and physical
operations.
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