valve which may be screwed into the opening or withdrawn from it, according
to the operator's judgment. The needle valve ends in a milled nut outside
the torch handle, this being the adjustment provided for the different
nozzles.

_Torch Construction._--A well designed torch is so designed that the
weight distribution is best for holding it in the proper position for
welding. When a torch is grasped by its handle with the gas hose attached,
it should balance so that it does not feel appreciably heavier on one end
than on the other.

The head and nozzle may be placed so that the flame issues in a line at
right angles with the torch body, or they may be attached at an angle
convenient for the work to be done. The head set at an angle of from 120 to
170 degrees with the body is usually preferred for general work in welding,
while the cutting torch usually has its head at right angles to the body.

Removable nozzles have various size openings through them and the different
sizes are designated by numbers from 1 up. The same number does not always
indicate the same size opening in torches of different makes, nor does it
indicate a nozzle of the same capacity.

The design of the nozzle, the mixing chamber, the injector, when one is
used, and the size of the gas openings must be such that all these things
are suited to each other if a proper mixture of gas is to be secured. Parts
that are not made to work together are unsafe if used because of the danger
of a flash back of the flame into the mixing chamber and gas tubes. It is
well known that flame travels through any inflammable gas at a certain
definite rate of speed, depending on the degree of inflammability of the
gas. The easier and quicker the gas burns, the faster will the flame travel