separate lump of hot carbide is isolated from its neighbours by a
material which is also a very bad heat conductor; and the heat has but
little opportunity of distributing itself evenly. Moreover, although iron
or steel is a notably better conductor of heat than any of the other
substances present in the carbide vessel, it is, as a metal, only a poor
conductor, being considerably inferior in this respect to copper. If heat
dissipation were the only point to be studied in the construction of an
acetylene apparatus, far better results might be obtained by the
employment of copper for the walls of the carbide container; and possibly
in that case a generator of considerable size, fitted with a water-
jacketed decomposing vessel, might be free from the trouble of
overheating. Nevertheless it will be seen in Chapter VI. that the use of
copper is not permissible for such purposes, its advantages as a good
conductor of heat being neutralised by its more important defects.

When suitable precautions are not taken to remove the heat liberated in
an acetylene apparatus, the temperature of the calcium carbide
occasionally rises to a remarkable degree. Investigating this point, Caro
has studied the phenomena of heat production in a "dipping" generator--
_i.e._, an apparatus in which a cage of carbide is alternately
immersed in and lifted out of a vessel containing water. Using a
generator designed to supply five burners, he has found a maximum
recording thermometer placed in the gas space of the apparatus to give
readings generally between 60 deg. and 100 deg. C.; but in two tests out
of ten he obtained temperatures of about 160 deg. C. To determine the
actual temperature of the calcium carbide itself, he scattered amongst the
carbide charge fragments of different fusible metallic alloys which were
known to melt or soften at certain different temperatures. In all his ten
tests the alloys melting at 120 deg. C. were fused completely; in two tests
other alloys melting at 216 deg. and 240 deg. C. showed signs of fusion;