pieces of firebrick so that it will remain stationary during the operation.

Holders for supporting the tanks of gas may be
made or purchased in forms that rest directly on the floor or that are
mounted on wheels. These holders are quite useful where the floor or ground
is very uneven.

_Hose._--All permanent lines from tanks and generators to the torches
are made with piping rigidly supported, but the short distance from the end
of the pipe line to the torch itself is completed with a flexible hose so
that the operator may be free in his movements while welding. An accident
through which the gases mix in the hose and are ignited will burst this
part of the equipment, with more or less painful results to the person
handling it. For that reason it is well to use hose with great enough
strength to withstand excessive pressure.

A poor grade of hose will also break down inside and clog the flow of gas,
both through itself and through the parts of the torch. To avoid outside
damage and cuts this hose is sometimes encased with coiled sheet metal.
Hose may be secured with a bursting strength of more than 1,000 pounds to
the square inch. Many operators prefer to distinguish between the oxygen
and acetylene lines by their color and to allow this, red is used for the
oxygen and black for acetylene.

_Other Materials._--Sheet asbestos and asbestos fibre in flakes are
used to cover parts of the work while preparing them for welding and during
the operation itself. The flakes and small pieces that become detached from
the large sheets are thrown into a bin where the completed small work is
placed to allow slow and even cooling while protected by the asbestos.