only substance to which any necessary quantity of heat can be safely or
conveniently transmitted, it follows that the larger in size an acetylene
generator is, or the more rapidly that generator is made to deliver gas,
the more desirable is it to use water as the means for dissipating the
surplus heat, and the more necessary is it to employ an apparatus in
which water is in large chemical excess at the actual place of
decomposition.

The argument is sometimes advanced that an acetylene generator containing
carbide in excess will work satisfactorily without exhibiting an
undesirable rise in internal temperature, if the vessel holding the
carbide is merely surrounded by a large quantity of cold water. The idea
is that the heat evolved in that particular portion of the charge which
is suffering decomposition will be communicated with sufficient speed
throughout the whole mass of calcium carbide present, whence it will pass
through the walls of the containing vessel into the water all round.
Provided the generator is quite small, provided the carbide container is
so constructed as to possess the maximum of superficial area with the
minimum of cubical capacity (a geometrical form to which the sphere, and
in one direction the cylinder, are diametrically opposed), and provided
the walls of the container do not become coated internally or externally
with a coating of lime or water scale so as to diminish in heat-
transmitting power, an apparatus designed in the manner indicated is
undoubtedly free from grave objection; but immediately any of those
provisions is neglected, trouble is likely to ensue, for the heat will
not disappear from the place of actual reaction at the necessary speed.
Apparent proof that heat is not accumulating unduly in a water-jacketed
carbide container even when the generator is evolving gas at a fair speed
is easy to obtain; for if, as usually happens, the end of the container
through which the carbide is inserted is exposed to the air, the hand may