safe to carry the heating to the point indicated by the magnet in the
absence of suitable means of measuring accurately these high temperatures.
In using a magnet for testing, it will be most satisfactory if it is an
electromagnet and not of the permanent type. The electric current may be
secured from any small battery and will be the means of making sure of the
test. The permanent magnet will quickly lose its power of attraction under
the combined action of the heat and the jarring to which it will be
subjected.

In reheating the work it is necessary to make sure that no part reaches a
temperature above that desired for best grain size and also to see that all
parts are brought to this temperature. Here enters the greatest difficulty
in restoring the metal. The heating may be done so slowly that no part of
the work on the outside reaches too high a temperature and then keeps the
outside at this heat until the entire mass is at the same temperature. A
less desirable way is to heat the outside higher than this temperature and
allow the conductivity of the metal to distribute the excess to the inside.

The most satisfactory method, where it can be employed, is to make use of a
bath of some molten metal or some chemical mixture that can be kept at the
exact heat necessary by means of gas fires that admit of close regulation.
The temperature of these baths may be maintained at a constant point by
watching a pyrometer, and the finished work may be allowed to remain in the
bath until all parts have reached the desired temperature.


WELDING INFORMATION

The following tables include much of the information that the operator must
use continually to handle the various metals successfully. The temperature