Molten lead is a good heating agent for tempering steel articles of unequal thickness, as these can be heated more uniformly by this method than by placing in an open fire or by supporting on an iron plate over a fire. Lead melts uniformly at a temperature of 612' F., and by alloying the lead with tin in varying proporv-ons, as explained in the table below, an extensive range of temperatures may be obtained. In using such baths, cover the surface with powdered charcoal to prevent the oxidation of the molten metal.

Colour.

Articles to be Tempered.

Composition, of Bath.

Temperature in degrees F.

Lead.

Tin.

Yellowish tint

Lancets.........

7

4

420°

Other surgical instruments .........

7.5

4

430°

Razors, etc.......

8

4

442"

Pale yellow ...

Penknives, and some implements of surgery .........

8 1/2

4

450

Straw yellow...

Large penknives, scalpels, etc.

1C

4

470o

Scissors, shears, garden hoes, cold chisels, etc.......

14

4

490°

Brown yellow

Axes, firmer chisels, plane irons, pocket-knives, etc.......

19

4

509°

Light purple ...

Table - knives, large shears, etc.......

30

4

530°

Dark purple ...

Swords, watch-springs, etc.......

48

4

550°

Clear blue

Large springs, daggers, augers, fine saws, etc......

50

2

558°

Pale blue

Pit saws, hand saws, and some springs ...

Boiling linseed oil 600o

Greenish blue

Articles which require to be somewhat softer......

Molten lead

612°