CHAPTER XLIII. METALS AND THEIR ALLOYS.

METALS AND THEIR ALLOYS.

222. Comparison of Metals and Non-Metals.--The majority of
elements are metals, only about a dozen being non-metallic in
their properties. The division line between the two classes is
not very well defined; e.g. As has certain properties which ally
it to metals; it has other properties which are non-metallic. H
occupies a place between the two classes. The following are the
more marked characteristics of each group: -

METALS.

1. Metals are solid at ordinary temperatures, and usually of high
specific gravity.

Exceptions: Hg is liquid above -39.5 degees; Li is the lightest
solid known; Na and K will float on water.

2. Metals reflect light in a way peculiar to themselves. They
have what is called a metallic luster.

3. They are white or gray. Exceptions: Au, Ca, Sr are yellow; Cu
is red.

4. In general they conduct heat and electricity well.

NON-METALS. 1. Non-metals are either gaseous or solid at ordinary
temperatures, and of low specific gravity. Exceptions: Br is a
liquid; I has the heaviest known vapor.

2. Non-metallic solids have different lusters, as glassy,
resinous- silky, etc. Exceptions: I, B, and C have metallic
luster.

3. Non-metals have no characteristic color.

4. They are non-conductors of heat and electricity. Exceptions: C
and some others are conductors. 5. They are usually malleable and
ductile.

6. They form alloys, or "chemical mixtures," with one another,
similar to other solutions. Exceptions: Some, as Ph and Zn, will
not alloy with one another.

7. Metals are electro-positive elements, and unite with O and H
to form bases. Exceptions: Some of the less electro-positive
metals, with a large quantity of O, form acids, as Cr, As, etc.

Numbers 2, 6, and 7 are the most characteristic and important
properties.

5. They are deficient in malleability and ductility.

6. They often form liquid solutions, similar to alloys in metals.

7. Non-metals are electronegative, and with H, or with H and O,
form acids.

Examine brass, bronze, bell-metal, pewter, German silver, solder,
type-metal.

223. Alloys.-An alloy is not usually a definite chemical
compound, but rather a mixture of two or more metals which are
melted together. One metal may be said to dissolve in the other,
as sugar dissolves in water. The alloy has, however, different
properties from those of its elements. For example, plumber's
solder melts at a lower temperature than either Ph or Sn, of
which it is composed. Some metals can alloy in any proportions.
Solder may have two parts of Sn to one of Pb, two of Pb to one of
Sn, or equal parts of each, or the two elements may alloy in
other proportions. Not all metals can be thus fused together
indefinitely; e.g., Zn and Pb. Nickel and silver coins are
alloyed with Cu, gold coins with Cu and Ag.

Gun-metal, bell-metal, and speculum-metal are each alloys of Cu
and Sn. Speculum-metal, used for reflectors in telescopes, has
relatively more Sn than either of the others; gun-metal has the
least. An alloy of Sb and Pb is employed for type-metal as it
expands at the instant of solidification. Pewter is composed of
Sn and Pb; brass, of Cu and Zn; German silver, of brass and Ni;
bronze, of Cu, Sn, and Zn; aluminium bronze, of Cu and Al.

224. Low Fusibility is a feature of many alloys. Wood's metal,
composed of Pb eight parts, Bi fifteen, Sn four, Cd three, melts
at just above 60 degrees, or far below the boiling-point of
water. By varying the proportions, different fusing-points are
obtained. This principle is applied in automatic fire alarms, and
in safety plugs for boilers and fire extinguishers. Water pipes
extend along the ceiling of a building and are fitted with plugs
of some fusible alloy, at short distances apart. When, in case of
fire, the heat becomes sufficiently intense, these plugs melt and
the water flows out.

225. Amalgams.--An amalgam is an alloy of Hg and another metal.
Mirrors are "silvered" with an amalgam of Sn. Tin-foil is spread
on a smooth surface and covered with Hg, and the glass is pressed
thereon.

Various amalgams are employed for filling teeth, a common one
being composed of Hg, Ag, and Sn. Au or Ag, with Hg, forms an
amalgam used for plating. Articles of gold and silver should
never be brought in contact with Hg. If a thin amalgam cover the
surface of a gold ring or coin, Hg can be removed with HNO3, as
Au is not attacked by it. Would this acid do in case of silver
amalgam? Heat will also quickly cause Hg to evaporate from Au.