for the contraction that is certain to follow, there will be a breakage at
some point. It is not possible to weld the simplest shapes, other than
straight bars, without considering this difficulty and making provision to
take care of it.

The exact method to employ in preheating will always call for good judgment
on the part of the workman, and he should remember that the success or
failure of his work will depend fully as much on proper preparation as on
correct handling of the weld itself. It should be remembered that the outer
flame of the oxy-acetylene torch may be depended on for a certain amount of
preheating, as this flame gives a very large volume of heat, but a heat
that is not so intense nor so localized as the welding flame itself. The
heat of this part of the flame should be fully utilized during the
operation of melting the metal and it should be so directed, when possible,
that it will bring the parts next to be joined to as high a temperature as
possible.

When the work has been brought to the desired temperature, all parts except
the break and the surface immediately surrounding it on both sides should
be covered with heavy sheet asbestos. This protecting cover should remain
in place throughout the operation and should only be moved a distance
sufficient to allow the torch flame to travel in the path of the weld. The
use of asbestos in this way serves a twofold purpose. It retains the heat
in the work and prevents the breakage that would follow if a draught of air
were to strike the heated metal, and it also prevents such a radiation of
heat through the surrounding air as would make it almost impossible for the
operator to perform his work, especially in the case of large and heavy
castings when the amount of heat utilized is large.

_Cleaning and Champfering._--A perfect weld can never be made unless