is doing its work, the tip may become excessively hot due to the heat
radiated from the molten metal. The tip may be cooled by turning off the
acetylene and dipping in water with a slight flow of oxygen through the
nozzle to prevent water finding its way into the mixing chamber.

The regulators for cutting are similar to those for welding, except that
higher pressures may be handled, and they are fitted with gauges reading up
to 200 or 250 pounds pressure.

In welding metals which conduct the heat very rapidly it is necessary to
use a much larger nozzle and flame than for metals which have not this
property. This peculiarity is found to the greatest extent in copper,
aluminum and brass.

Should a hole be blown through the work, it may be closed by withdrawing
the flame for a few seconds and then commencing to build additional metal
around the edges, working all the way around and finally closing the small
opening left at the center with a drop or two from the welding rod.


WELDING VARIOUS METALS

Because of the varying melting points, rates of expansion and contraction,
and other peculiarities of different metals, it is necessary to give
detailed consideration to the most important ones.

_Characteristics of Metals._--The welder should thoroughly understand
the peculiarities of the various metals with which he has to deal. The
metals and their alloys are described under this heading in the first
chapter of this book and a tabulated list of the most important points