The principal use of tin is for protective platings on household utensils
and in wrappings of tin-foil. Tin forms an important part of many alloys
such as babbitt, Britannia metal, bronze, gun metal and bearing metals.

_Nickel_ is important in mechanics because of its combinations with
other metals as alloys. Pure nickel is grayish-white, malleable, ductile
and tenacious. It weighs almost as much as steel and, next to manganese, is
the hardest of metals. Nickel is one of the three magnetic metals, the
others being iron and cobalt. The commonest alloy containing nickel is
german silver, although one of its most important alloys is found in nickel
steel. Nickel is about ten per cent heavier than steel, and has a tensile
strength of 90,000 pounds per square inch.

_Platinum._--This metal is valuable for two reasons: it is not
affected by the air or moisture or any ordinary acid or salt, and in
addition to this property it melts only at the highest temperatures. It is
a fairly good electrical conductor, being better than iron or steel. It is
nearly three times as heavy as steel and its tensile strength is 25,000
pounds per square inch.


ALLOYS

An alloy is formed by the union of a metal with some other material, either
metal or non-metallic, this union being composed of two or more elements
and usually brought about by heating the substances together until they
melt and unite. Metals are alloyed with materials which have been found to
give to the metal certain characteristics which are desired according to
the use the metal will be put to.