It was only with great difficulty that the obstacles in the way of
successfully using acetylene were overcome by the development of
practicable controlling devices and torches, as well as generators. At
present the oxy-acetylene process is the most universally adaptable, and
probably finds the most widely extended field of usefulness of any welding
process.

The theoretical proportion of the gases for perfect combustion is two and
one-half volumes of oxygen to one of acetylene. In practice this proportion
is one and one-eighth or one and one-quarter volumes of oxygen to one
volume of acetylene, so that the cost is considerably reduced below what it
would be if the theoretical quantity were really necessary, as oxygen costs
much more than acetylene in all cases.

While the heat is so intense as to fuse anything brought into the path of
the flame, it is localized in the small "welding cone" at the torch tip so
that the torch is not at all difficult to handle without special protection
except for the eyes, as already noted. The art of successful welding may be
acquired by any operator of average intelligence within a reasonable time
and with some practice. One trouble met with in the adoption of this
process has been that the operation looks so simple and so easy of
performance that unskilled and unprepared persons have been tempted to try
welding, with results that often caused condemnation of the process, when
the real fault lay entirely with the operator.

The form of torch usually employed is from twelve to twenty-four inches
long and is composed of a handle at one end with tubes leading from this
handle to the "welding head" or torch proper. At or near one end of the
handle are adjustable cocks or valves for allowing the gases to flow into