The great heat needed for the purpose of uniting two or more pieces of
metal so as to make of them an autogenous whole is obtained, in this
process, by the burning of acetylene gas in conjunction with oxygen.

Carbide, looking like little lumps of granite, is placed in a tray at
the bottom of the generator for acetylene gas, which is of the form
of a small portable gasometer. The tap, admitting water to the carbide
trays, is turned on, and gas at once generates, and forces up the
generator in the way so familiar to those who often see a gasometer.
This gas passes through a tube to the blow-pipe of the welder, or to
any other use for which it is destined.

[Illustration: TRAINING WOMEN AS AEROPLANE BUILDERS]

In oxy-acetylene welding, the process employs the flame produced by
the combustion in a suitable blow-pipe of oxygen and acetylene. When
a light is applied to the nozzle of the pipe a yellow flame, a foot
long, flares up, and in the centre of it, close to the nozzle, appears
a very small, dazzling, bluish flame, which can only safely be gazed
upon by eyes protected by coloured glasses. The temperature of this
flame at the apex is about 6,300 degrees Fahr., and it is with this
that the metals to be welded together are brought to a suitable degree
of heat.

The workers' eyes are protected by black goggles, their hair confined
by caps or handkerchiefs, and overalls or leather-aprons protect their
clothes from the sparks and also from the smuts which naturally
accrue on surrounding objects. Each welder holds in her right hand the
blow-pipe of the craft, from which depends two long flexible tubes,