Metals may be known from all other substances by certain properties:
they have that peculiar brilliancy, called, for that reason, the
“metallic” lustre; they are rapidly heated, and as rapidly cool,
hence they are said to be good conductors of heat; they are all
opaque, and most of them very heavy; some indeed, as gold and
platinum, are the heaviest substances known, being about twenty times
heavier than water; they have, moreover, other valuable properties
such as the capability of being melted, of being drawn out into wire,
of being beaten into thin plates, &c.
All metals are simple bodies; that is to say, they cannot be made
out of other substances, although two or more metals may be combined
and be again separated, or they may be combined with numerous other
substances, as oxygen, and also again separated. There are upwards
of fifty metals known to chemists, yet but few are used to any extent
in the arts or manufactures. All the metals in use for the very many
purposes to which they are applied are not simple metals, but are
what are called “alloys,” that is to say, compounds of two or more
metals. The chief metals in use are--
IRON, MERCURY,
COPPER, NICKEL,
LEAD, GOLD,
TIN, SILVER,
ZINC, PLATINUM.
But in the state of oxide many are used which are seldom seen in the
metallic state, such are the earths and alkalies; and for colors, and
several other purposes, many other preparations are in use. The chief
alloys, or compound metals in use, are, brass, made of copper and
zinc; pewter, made of lead and tin; bell metal and gun metal, made
of copper and tin; and solder, which is a kind of pewter, and made of
the same metals; the silvering for looking-glasses is made of mercury
and tin; the gold and silver used for coin are not pure metals, but
alloyed with two parts of silver or copper to every twenty-two of the
pure metal, and this forms the “standard” gold or silver. The gold
used by jewellers has often a much greater proportion of alloy--for
this name is given both to a compound metal and the cheaper metal
made to combine with the more precious. The object gained by thus
alloying the coinage, is that of rendering the metals harder, so that
they shall not suffer much loss in wearing; thus a small quantity
of copper mixed with either gold or silver, renders them both harder,
although itself softer than either. The combination of certain metals
forming alloys, is often not exactly the mean of their respective
qualities, for instance, a small quantity of silver is sometimes
fused with cast steel for penknife blades, and although the silver is
itself much softer than the steel, yet the combination is found to be
both closer in the grain and harder; it is known as silver-steel in
commerce. Bismuth, although itself not very fusible, increases the
fusibility of other metals; a combination of 2 parts tin, 3 lead, and
5 bismuth, forms a metal fusible by boiling water.