torches, and with very small work the outer flame of the welding torch
automatically provides means to this end.

The temperature of the parts heated should be gradually raised in all
cases, giving the entire mass of metal a chance to expand equally and to
adjust itself to the strains imposed by the preheating. After the region
around the weld has been brought to a proper temperature the opening to be
filled is exposed so that the torch flame can reach it, while the remaining
surfaces are still protected from cold air currents and from cooling
through natural radiation.

One of the commonest methods and one of the best for handling work of
rather large size is to place the piece to be welded on a bed of fire brick
and build a loose wall around it with other fire brick placed in rows, one
on top of the other, with air spaces left between adjacent bricks in each
row. The space between the brick retaining wall and the work is filled with
charcoal, which is lighted from below. The top opening of the temporary
oven is then covered with asbestos and the fire kept up until the work has
been uniformly raised in temperature to the desired point.

When much work of the same general character and size is to be handled, a
permanent oven may be constructed of fire brick, leaving a large opening
through the top and also through one side. Charcoal may be used in this
form of oven as with the temporary arrangement, or the heat may be secured
from any form of burner or torch giving a large volume of flame. In any
method employing flame to do the heating, the work itself must be protected
from the direct blast of the fire. Baffles of brick or metal should be
placed between the mouth of the torch and the nearest surface of the work
so that the flame will be deflected to either side and around the piece
being heated.