prevented from being saturated with carbon, which would prove very
detrimental to its strength. A secondary advantage is found in the fact
that the greatest heat is at the metal being welded because of its being
the positive electrode.

The carbon electrode is usually made from one quarter to one and a half
inches in diameter and from six to twelve inches in length. The length of
the arc may be anywhere from one inch to four inches, depending on the size
of the work being handled.

While the parts are carefully insulated to avoid danger of shock, it is
necessary for the operator to wear rubber gloves as a further protection,
and to wear some form of hood over the head to shield him against the
extreme heat liberated. This hood may be made from metal, although some
material that does not conduct electricity is to be preferred. The work is
watched through pieces of glass formed with one sheet, which is either blue
or green, placed over another which is red. Screens of glass are sometimes
used without the head protector. Some protection for the eyes is absolutely
necessary because of the intense white light.

It is seldom necessary to preheat the work as with the gas processes,
because the heat is localized at the point of welding and the action is so
rapid that the expansion is not so great. The necessity of preheating,
however, depends entirely on the material, form and size of the work being
handled. The same advice applies to arc welding as to the gas flame method
but in a lesser degree. Filling rods are used in the same way as with any
other flame process.

It is the purpose of this explanation to state the fundamental principles
of the application of the electric arc to welding metals, and by applying