is lighted at the torch tip. The adjustment should cause the presence of a
greenish-white cone of flame surrounded by a larger body of burning gas,
the cone starting at the mouth of the torch.

[Illustration: Figure 24.--Acetylene-Air Torch]

By opening the tank valve more, a longer and hotter flame is produced, the
length being regulated by the tank valve also. This torch will give
sufficient heat to melt steel, although not under conditions suited to
welding. Because of the excess of acetylene always present there is no
danger of oxidizing the metal being heated.

The only care required by this torch is to keep the small air passages at
the nozzle clean and free from carbon deposits. The flame should be
extinguished when not in use rather than turned low, because this low flame
rapidly deposits large quantities of soot in the burner.




CHAPTER V

OXY-ACETYLENE WELDING PRACTICE


PREPARATION OF WORK

_Preheating._--The practice of heating the metal around the weld
before applying the torch flame is a desirable one for two reasons. First,
it makes the whole process more economical; second, it avoids the danger of