temperature, in the bath for at least 30 min., insuring uniformity
of temper; then cool in the bath, atmosphere or oil.

If higher drawing temperatures are desired than those possible
with oil, a salt bath can be used. A very excellent bath is made
by mixing two parts by weight of crude potassium nitrate and three
parts crude sodium nitrate. These will melt at about 450 deg.F. and
can be used up to 1,000 deg.F. Before heating the steel in the salt
bath, slowly preheat, preferably in oil. Reheating the hardened
high-speed steel to 1,000 deg.F. will materially increase the life
of lathe tools, but milling and form cutters, taps, dies, etc.,
should not be reheated higher than 500 to 650 deg.F., unless extreme
hardness is required, when 1,100 to 1,000 deg.F., will give the hardest
edge.

INSTRUCTIONS FOR WORKING HIGH-SPEED STEEL

Owing to the wide variations in the composition of high-speed steels
by various makers, it is always advisable to follow the directions
of each when using his brand of steel. In the absence of specific
directions the following general suggestions from several makers
will be found helpful.

The Ludlum Steel Company recommend the following:

CUTTING-OFF.--To cut a piece from an annealed bar, cut off with
a hack saw, milling cutter or circular saw. Cut clear through the
bar; do not nick or break. To cut a piece from an unannealed bar,
cut right off with an abrasive saw; do not nick or break. If of
large cross-section, cut off hot with a chisel by first slowly
and uniformly heating the bar, at the point to be cut, to a good
lemon heat, 1,800 deg.-1,850 deg.F. and cut right off while hot; do not nick
or break. Allow the tool length and bar to cool before reheating
for forging.

LATHE AND PLANER TOOLS

TO FORGE.--Gently warm the steel to remove any chill is particularly
desirable in the winter. Then heat slowly and carefully to a scaling
heat, that is a lemon heat (1,800 deg.-2,000 deg.F.), and forge uniformly.
Reheat the tool for further forging directly the steel begins to
stiffen under the hammer. Under no circumstances forge the steel
when the temperature falls below a dark lemon to an orange color:
about 1,700 deg.F. Reheat as often as is necessary to finish forging
the tool to shape. Allow the tool to cool after forging by burying
the tool in dry ashes or lime. Do not place on the damp ground
or in a draught of air.

The heating for forging should be done preferably in a pipe or
muffl