it is used again. It is right here that the greatest carelessness
is generally encountered.

Don't pack the work to be carburized too closely; leave at least
1 in. from the bottom, 3/4 in. from the sides, and 1 in. from the
top of pots, and for a 6-hr. run, have the pieces at least 1/2
in. apart. This gives the heat a chance to thoroughly permeate
the pot, and the carburizing material a chance to shrink without
allowing carburized pieces to touch and cause soft spots.

Good case-hardening pots and annealing tubes can be made from the
desired size of wrought iron pipe. The ends are capped or welded,
and a slot is cut in the side of the pot, equal to one quarter of
its circumference, and about 7/8 of its length. Another piece of
the same diameter pipe cut lengthwise into thirds forms a cover
for this pot. We then have a cheap, substantial pot, non-warping,
with a minimum tendency to scale, but the pot is difficult to seal
tightly. This idea is especially adaptable when long, narrow pots
are desired.

When pots are packed and the carburizer thoroughly tamped down,
the covers of the pot are put on and sealed with fire clay which
has a little salt mixed into it. The more perfect the seal the
more we can get out of the carburizer. The rates of penetration
depend on temperature and the presence of proper gas in the required
volume. Any pressure we can cause will, of course, have a tendency
to increase the rate of penetration.

If you have a wide furnace, do not load it full at one time. Put
one-half your load in first, in the center of the furnace, and
heat until pots show a low red, about 1,325 to 1,350 deg.F. Then fill
the furnace by putting the cold pots on the outside or, the section
nearest the source of heat. This will give the work in the slowest
portion of the furnace a chance to come to heat at the same time
as the pots that are nearest the sources of heat.

To obtain an even heating of the pots and lessen their tendency
to warp and scale, and to cause the contents of the furnace to
heat up evenly, we should use a reducing fire and fill the heating
chamber with flame. This can be accomplished by partially closing
the waste gas vents and reducing slightly the amount of air used
by the burners. A short flame will then be noticed issuing from
the partially closed vents. Thus, while maintaining the temperature
of the heating chamber, we will have a lower temperature in the
combustion chamber, which will naturally