nd quality of the case and the condition of the
core. The gears are each tested in this way at several points on
the teeth and elsewhere, the scrap gear being also subjected to
the test. Finally, the scrap gear is securely clamped in the
straightening press shown in Fig. 57. With a 3-1/2-lb. hammer and
a suitable hollow-ended drift manipulated by one of Sandow's
understudies, teeth are broken out of the scrap gear at various
points. These give a record confirming the center-punch tests,
which, if the angle of the center punch is kept at 120 deg. and
the weight of the hammer and blow are uniform, is very accurate.

After passing the center-punch test the ends of the teeth are peened
lightly with a hammer. If they are too hard, small particles fly
off. Such gears are drawn in oil at a temperature of from 300 to
350 deg.F., depending on their hardness. Some builders prefer to have
the extreme outer ends of the teeth drawn somewhat lower than the
rest. This drawing is done on gas-heated red-hot plates, as shown
at _A_ in Fig. 58.

[Illustration: FIG. 57.--Press for holding test gears for breaking.]

Nickel steel, in addition to all the tests given to carbon steel,
is subjected to a Brinell test. For each steel, the temperature
and the period of treatment are specific. For some unknown reason,
apparently like material with like treatment will, in isolated
cases, not produce like results. It then remains for the treatment
to be repeated or modified, but the results obtained during inspection
form a valuable aid to the metallurgist in determining further
treatment.

TEMPERATURE RECORDING AND REGULATION.--Each furnace is equipped
with pyrometers, but the reading and recording of all temperatures
are in the hands of one man, who occupies a room with an opening
into the end of the hardening department. The opening is about 15
ft. above the floor level. On each side of it, easily legible from
all of the furnaces, is a board with the numbers of the various
furnaces, as shown in Figs. 59 and 60. Opposite each furnace number
is a series of hooks whereon are hung metal numbers representing the
pyrometer readings of the temperature in that particular furnace.
Within the room, as shown in Fig. 60, the indicating instrument
is to the right, and to the left is a switchboard to connect it
with the thermo-couples in the various furnaces. The boards shown
to the right and the left swing into the room, which enables the
attendant easily