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.

Nevertheless the production of a temperature somewhat exceeding 100 deg. C.
among the lumps of carbide actually undergoing decomposition can hardly
be avoided in any practical generator. Based on a suggestion in the
"Report of the Committee on Acetylene Generators" which was issued by the
British Home Office in 1902, Fouche has proposed that 130 deg. C., as
measured with the aid of fusible metallic rods, [Footnote: An alloy made
by melting together 55 parts by weight of commercial bismuth and 45 parts
of lead fuses at 127 deg. C., and should be useful in performing the tests.]
should be considered the maximum permissible temperature in any part of a
generator working at full speed for a prolonged period of time. Fouche
adopts this figure on the ground that 130 deg. C. sensibly corresponds with
the temperature at which a yellow substance is formed in a generator by a
process of polymerisation; and, referring to French conditions, states
that few actual apparatus permit the development of so high a