_Copper._--The principal copper alloys include brass, bronze, german
silver and gun metal.

Brass is composed of approximately one-third zinc and two-thirds copper. It
is used for bearings and bushings where the speeds are slow and the loads
rather heavy for the bearing size. It also finds use in washers, collars
and forms of brackets where the metal should be non-magnetic, also for many
highly finished parts.

Brass is about one-third as good an electrical conductor as copper, is
slightly heavier than steel and has a tensile strength of 15,000 pounds
when cast and about 75,000 to 100,000 pounds when drawn into wire.

Bronze is composed of copper and tin in various proportions, according to
the use to which it is to be put. There will always be from six-tenths to
nine-tenths of copper in the mixture. Bronze is used for bearings,
bushings, thrust washers, brackets and gear wheels. It is heavier than
steel, about 1/15 as good an electrical conductor as pure copper and has a
tensile strength of 30,000 to 60,000 pounds.

Aluminum bronze, composed of copper, zinc and aluminum has high tensile
strength combined with ductility and is used for parts requiring this
combination.

Bearing bronze is a variable material, its composition and proportion
depending on the maker and the use for which it is designed. It usually
contains from 75 to 85 per cent of copper combined with one or more
elements, such as tin, zinc, antimony and lead.

White metal is one form of bearing bronze containing over 80 per cent of