out from the die than the high carbon stock. Nickel steel welds readily,
the nickel increasing the strength of the weld.

Iron and copper may be welded together by reducing the size of the copper
end where it comes in contact with the iron. When welding copper and brass
the pressure must be less than when welding iron. The metal is allowed to
actually fuse or melt at the juncture and the pressure must be sufficient
to force the burned metal out. The current is cut off the instant the metal
ends begin to soften, this being done by means of an automatic switch which
opens when the softening of the metal allows the ends to come together. The
pressure is applied to the weld by having the sliding jaw moved by a weight
on the end of an arm.

Copper and brass require a larger volume of current at a lower voltage than
for steel and iron. The die faces are set apart three times the diameter of
the stock for brass and four times the diameter for copper.

Light gauges of sheet steel can be welded to heavy gauges or to solid bars
of steel by "spot" welding, which will be described later. Galvanized iron
can be welded, but the zinc coating will be burned off. Sheet steel can be
welded to cast iron, but will pull apart, tearing out particles of the
iron.

Sheet copper and sheet brass may be welded, although this work requires
more experience than with iron and steel. Some grades of sheet aluminum can
be spot-welded if the slight roughness left on the surface under the die
is not objectionable.

_Butt Welding._--This is the process which joins the ends of two
pieces of metal as described in the foregoing part of this chapter. The