Hardening

—1. Increasing the hardne of wh metals either by suddenly cooling them after intense heat, or by subjecting them to hydraulic pre ure while cooling slowly. 2. The preliminary proce of tempering edge tools; the tool, being heated to a cherry red, is plunged into brine or clear water, the sudden quenching rendering it hard enough to scratch gla . Subsequent reheating, to a point determined by experience and judgment, is nece ary to draw the temper, so that the steel shall have those qualities of hardne and toughne nece ary for its desired duties.