The article, after being completed, is hardened by being heated gradually to a bright red, and then plunged into cold Water: it is then tempered by being warmed gradually and equably either over a fire, or on a piece of heated metal, till of the color cor responding to the purpose for which it is required, as per ble below; when it is again plunged into water.

Corresponding Temperature

A very pale straw, -

4.30

Lancts.

Straw,......

400

Razors.

Darker Straw - - -

470

Penknives.

All kinds of wood tools.

Yellow,.....

490

Scissors.

Screw taps

Brown yellow, - - -

500

Hatchets, chipping chisels,

Slightly tinged purple,

520

Saws.

Slightly tinged purple.....

530

All kinds of percussive tools.

Dark purple, - - -

650

Springs.

Blue,......

570

Dark blue, - - - -

600

Soft for saws.