iron turns to ordinary cast iron if kept heated for any length of time.

_Steel._--Steel should be beveled if more than one-eighth inch in
thickness. It requires only a local preheating around the point to be
welded. The welding flame should be absolutely neutral, without excess of
either gas. If the metal is one-sixteenth inch or less in thickness, the
tip of the blue-white cone must be held a short distance from the surface
of the work; in all other cases the tip of this cone is touched to the
metal being welded.

The welding rod may be of mild, low carbon steel or of Norway iron. Nickel
steel rods may be used for parts requiring great strength, but vanadium
alloys are very difficult to handle. A very satisfactory rod is made by
twisting together two wires of the required material. The rod must be kept
constantly in contact with the work and should not be added until the edges
are thoroughly melted. The flux may or may not be used. If one is wanted,
it may be made from three parts iron filings, six parts borax and one part
sal ammoniac.

It will be noticed that the steel runs from the flame, but tends to hold
together. Should foaming commence in the molten metal, it shows an excess
of oxygen and that the metal is being burned.

High carbon steels are very difficult to handle. It is claimed that a drop
or two of copper added to the weld will assist the flow, but will also
harden the work. An excess of oxygen reduces the amount of carbon and
softens the steel, while an excess of acetylene increases the proportion of
carbon and hardens the metal. High speed steels may sometimes be welded if
first coated with semi-steel before welding.