The difference in temperature
between the acetylene and the carbide in Caro's test accentuates the
difficulty of gauging the heat in a carbide vessel by mere external
touch, and supplies experimental proof of the previous assertions as to
the low heat-conducting power of calcium carbide and of the gases of the
decomposing vessel. It must not be supposed that temperatures such as
Lewes has found ever occur in any commercial generator of reasonably good
design and careful construction; they must be regarded rather as
indications of what may happen in an acetylene apparatus when the
phenomena accompanying the evolution of gas are not understood by the
maker, and when all the precautions which can easily be taken to avoid
excessive heating have been omitted, either by building a generator with
carbide in excess too large in size, or by working it too rapidly, or
more generally by adopting a system of construction unsuited to the ends
in view. The fact, however, that Lewes has noted the production of a
temperature of 807 deg. C. is important; because this figure is appreciably
above the point 780 deg. C., at which acetylene decomposes into its elements
in the absence of air.
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