The so-called white metals are employed almost exclusively for bearings. (See Anti-friction Metals under Alloys.) In the technology of mechanics an accurate distinction is made between the different kinds of metals for bearings; and they may be classed in two groups, red brass and white metal. The red-

brass bearings are characterized by great hardness and power of resistance, and are principally used for bearings of heavily loaded and rapidly revolving axles. For the axles of large and heavy flywheels, revolving at great speed, bearings of red brass are preferable to white metal, though more expensive.

In recent years many machinists have found it advantageous to substitute for the soft alloys generally in use for bearings a metal almost as hard as the axle itself. Phosphor bronze (q. v.) is frequently employed for this purpose, as it can easily be made as hard as wrought or cast steel. In this case the metal is used in a thin layer, and serves only, as it were, to fill out the small interstices caused by wear on the axle and bearing, the latter being usually made of some rather easily fusible alloy of lead and tin. Such bearings are very durable, but expensive, and can only be used for large machines. For small machines, running gently and uniformly, white-metal bearings are preferred, and do excellent work, if the axle is not too heavily loaded. For axles which have a high rate of revolution, bearings made of quite hard metals are chosen, and with proper care —which, indeed, must be given to bearings of any material—they will last for a long time without needing repair.

Other white bearing metals are:

XXI

Tin, 8.5; antimony, 10; copper, 5 parts.

XXII

Tin, 42; antimony, 16; lead, 42 parts.

XXIII

Tin, 72; antimony, 26; copper, 2 parts.

XXIV

Tin, 81; antimony, 12.5; copper, 6.5 parts.