It should require little attention. All machines have to be emptied and
recharged periodically; but the more this process is simplified and the
more quickly this can be accomplished, the better.

It should be provided with a suitable indicator to designate how low the
charge is in order that the refilling may be done in good season.

It should completely use up the carbide, generating the maximum amount of
gas.

_Overheating._--A large amount of heat is liberated when acetylene gas
is formed from the union of calcium carbide and water. Overheating during
this process, that is to say, an intense local heat rather than a large
amount of heat well distributed, brings about the phenomenon of
polymerization, converting the gas, or part of it, into oily matters, which
can do nothing but harm. This tarry mass coming through the small openings
in the torches causes them to become partly closed and alters the
proportions of the gases to the detriment of the welding flame. The only
remedy for this trouble is to avoid its cause and secure cool generation.

Overheating can be detected by the appearance of the sludge remaining after
the gas has been made. Discoloration, yellow or brown, shows that there has
been trouble in this direction and the resultant effects at the torches may
be looked for. The abundance of water in the carbide to water machines
effects this cooling naturally and is a characteristic of well designed
machines of this class. It has been found best and has practically become a
fundamental rule of generation that a gallon of water must be provided for
each pound of carbide placed in the generator. With this ratio and a
generator large enough for the number of torches to be supplied, little
trouble need be looked for with overheating.