METAL (Gr. μέταλλον), a term including about
50 elementary substances which possess, either
wholly or in part, certain well marked physical
and chemical properties, of which the most
universal and characteristic is lustre. The
peculiar brilliancy and reflective power of the
metals, which may be enhanced by polishing,
results from their great opacity. The color of
the metals is generally white with a grayish,
bluish, or pinkish tint; copper and gold are
the only exceptions. In extremely thin films
some of the metals allow the passage of certain
rays of light. Gold leaf transmits light of a
faint greenish hue. Most of the metals have
a high specific gravity, a property which was
regarded as characteristic until the discovery
of the alkaline metals, which are lighter than
water. With the exception of arsenic, they
may all be fused, the temperature required for
fusion varying from 100° F. to the highest
heat of the oxy-hydrogen blowpipe. Some
of the metals may be volatilized. Mercury,
the only liquid metal, is solidified at -39° F.
Arsenic when heated passes directly into vapor
without fusion. Most of the metals possess a
certain mobility of particles that allows of their
being extended or otherwise altered in form.
The two nearly related properties of malleability
and ductility, resulting from this, are not
possessed by the metals in the same degree.
A few of them, as antimony, arsenic, and
bismuth, are decidedly brittle. Some assume a
plastic condition before complete fusion,
notably iron and platinum; on this property
depends the operation of welding. The strength
of the metals is very dissimilar, iron in the
form of wire being about 26 times as tenacious
as lead. They are all conductors of heat and
electricity, although differing widely in this
respect. The metals at present known, with
the name of the discoverer and date of
discovery of each, together with their atomic
weights, are given in the following table:
METAL.
Atomic weight.
Discoverer.
Date of discovery.
Gold
197
Known to the ancients.
....
Silver
108
Known to the ancients.
....
Mercury
200
Known to the ancients.
....
Copper
63.4
Known to the ancients.
....
Lead
207
Known to the ancients.
....
Tin
118
Known to the ancients.
....
Iron
56
Known to the ancients.
....
Bismuth
210
Basilius Valentinus.
15th century
Antimony
122
Basilius Valentinus.
15th century
Zinc
65
First mentioned by Paracelsus
16th century
Arsenic
75
Schröder
1694
Cobalt
59
Brandt
1733
Platinum
197.4
Ulloa
1736
Nickel
59
Cronstedt
1751
Manganese
55
Gahn
1774
Molybdenum
96
Hjelm
1782
Tungsten (wolfram)
184
D'Elhujar
1783
Titanium
50
Gregor
1789
Yttrium
61.6
Gadolin
1794
Chromium
52.2
Vauquelin
1797
Tellurium
128
Klaproth
1798
Niobium (columbium)
94
Hatchett
1801
Tantalum
182
Ekeberg
1802
Palladium
106.6
Wollaston
1803
Osmium
199
Tennant
1803
Cerium
92
Klaproth, Hisinger, and Berzelius
1803
Iridium
198
Descotils and Tennant
1803-4
Rhodium
104.4
Wollaston
1804
Potassium
39.1
Davy
1807
Sodium
23
Davy
1807
Barium
137
Davy
1808
Strontium
87.6
Davy
1808
Calcium
40
Davy
1808
Lithium
7
Davy
1818
Cadmium
112
Stromeyer
1818
Zirconium (beryllium)
89.6
Berzelius
1824
Aluminum
27.4
Wöhler
1827
Glucinum
9.4
Wöhler and Bussy
1828
Thorium
115.7
Berzelius
1828
Magnesium
24
Davy
1828
Vanadium
51.3
Sefstrom
1830
Lanthanum
93.6
Mosander
1839
Uranium
120
Peligot
1840
Didymium
95
Mosander
1841
Erbium
112.6
Mosander
1843
Ruthenium
104
Claus
1846
Rubidium
85.4
Bunsen and Kirchhoff
1860
Cæsium
133
Bunsen and Kirchhoff
1860
Thallium
204
Crookes (Lamy)
1861
Indium
113.4
Reich and Richter
1863
With a few exceptions, the names and dates in
the above list refer to the actual production of
the metal. In many instances the metallic
compounds were known and studied long
before the metal itself was isolated. Some of
the rarer metals have never been prepared in
a pure form. Pelopium, formerly enumerated
among the metals, has been shown to have
no existence; and the existence of terbium is
doubtful. The last four metals were discovered
by means of the spectroscope.—The
following tables exhibit the mutual relations of
some of the more important metals in physical
properties:
The physical properties of the metals are largely
dependent on their purity and molecular
condition, and on temperature. Hammered,
rolled, or drawn metal generally has a higher
specific gravity than cast metal. The state of
molecular tension often induced by mechanical
working, especially when cold, is resolved by
annealing, i. e., heating and slow cooling.
Most of the metals are more malleable and
ductile at high temperatures. Commercial
zinc is only malleable between 100° and 150°
C.; at 200° it is so brittle that it can be
pulverized. The conductivity for electricity is
greatly diminished at high temperatures, and
also by the presence of impurities in the metal.
The addition of a small amount of a foreign
substance often makes a metal harder, more
rigid, and less susceptible of elongation. This
is notably the case with iron, which when pure
is soft and stretches considerably under strain
before breaking, while steel, which is iron
with a small amount of carbon, may be rigid
and brittle. If reference be had to the original
area of section, the rigid metal will show
the greatest strength under a gradually applied
tensile strain; but if to the fractured area, the
purer metal is the strongest. The tenacity of
metals generally decreases as the temperature
is raised. The fusing points of the more
refractory metals given in the above tables are
approximate only, since trustworthy methods
for determining high temperatures are wanting.
The metals vary greatly in hardness.
The alkaline metals are as soft as wax, while
some, as chromium, will scratch glass. It is
not improbable that extreme hardness in metals
is produced by the presence of some foreign
body, and is not inherent in the metal itself.
Most of the metals are capable of assuming a
distinctly crystalline form, generally belonging
to the regular or isometric system. Some, as
antimony and arsenic, crystallize in
rhombohedrons. A few of the metals occur native;
these are gold, platinum, palladium, iridium,
and rhodium, which are almost exclusively
found in the metallic state, and silver, copper,
mercury, bismuth, arsenic, and antimony.
Generally, however, the metals occur mineralized
in combination with oxygen or sulphur.
The specific heats of the metals, as will be
noticed in the above tables, are inversely as
their atomic weights, or, in other words, the
specific heats of the atoms of the metals are
equal.—Chemically, the metals present very
varied characters. As a class they are distinguished
by the formation of compounds with
oxygen which have basic characters, while the
non-metals as a class form oxides which have
acid characters. These two classes of oxides
are capable of combining to form salts. While
the oxides of the non-metals never form bases,
the higher oxides of many of the metals have
distinctly acid properties, and indeed a few of
the metals form only acid oxides. The most
stable compounds of tellurium, arsenic, antimony,
tungsten, titanium, molybdenum, and
vanadium with oxygen are acid in character
and capable of combining with basic oxides.
Those metals which seem to hold a position
intermediate between the two classes have been
termed half metals or metalloids. The latter
term, as now generally used, includes all the
non-metallic elements, viz.: hydrogen, oxygen,
bromine, chlorine, iodine, fluorine, boron,
nitrogen, phosphorus, selenium, silicon, sulphur,
and carbon. Tellurium is closely related to
sulphur and selenium, and is often classed with
the metalloids; but its metallic appearance,
and the analogy which its compounds bear to
those of antimony, render its association with
the metals equally appropriate. Hydrogen,
although a gas and the lightest body known,
resembles the metals in its chemical properties,
and is capable of replacing them in
combination. The formation of salts is regarded
in modern chemistry as the replacement of
hydrogen in the acid by a metal.—The metals
are variously classified. A natural grouping,
and one in common use, is: 1, metals of the
alkalies; 2, metals of the alkaline earths; 3,
metals of the earths proper; 4, oxidable
metals proper, whose oxides form powerful
bases; 5, oxidable metals, whose oxides form
weak bases or acids; 6, metals proper, whose
oxides are reduced by heat, called noble metals.
The strength of affinity of the different metals
for oxygen is the basis of a classification
formerly much used. It is embodied in part in
the electro-chemical series of Berzelius, which
played an important part in the development
of chemical science. The alkaline metals
oxidize rapidly in the air, and decompose water
at ordinary temperatures; others, as iron and
zinc, do not oxidize in pure dry air, and
decompose water only at a red heat, or in
contact with an acid; and others, as the noble
metals, do not decompose water at any
temperature. The electrical relations of the metals
correspond in general to their affinity for
oxygen. Thus, the alkaline metals are the most
electro-positive, and the noble metals the most
electro-negative. The metals likewise fall into
groups in which the individual members can
replace one another in compounds without
change of crystalline form; they are then said to
be isomorphous. As examples may be cited
magnesium, calcium, manganese, iron, zinc, copper,
and aluminum; barium, strontium, and lead;
sodium, silver, thallium, gold, and potassium;
arsenic, antimony, and bismuth; tin, titanium,
tungsten, and molybdenum; platinum, iridium,
and osmium. The atomicity of the elements,
or their combining values, forms the basis of
classification for study in modern chemistry.
Metals are thus divided into monads (or those
replaceable by or equivalent to one atom of a
monogenic element, as hydrogen or chlorine),
dyads, triads, tetrads, pentads, and hexads,
as follows: monads—lithium, sodium, potassium,
rubidium, calcium, silver; dyads—calcium,
strontium, barium, glucinum, yttrium,
lanthanum, didymium, erbium, thorium,
magnesium, zinc, cadmium, copper, mercury;
triads gold, thallium; tetrads titanium, tin,
aluminum, zirconium, rhodium, ruthenium,
palladium, platinum, iridium, osmium, lead,
manganese, iron, cobalt, nickel, cerium, indium,
uranium; pentads vanadium, arsenic,
antimony, bismuth, niobium, tantalum;
hexads—chromium, molybdenum, tungsten. A few of
the metals possess more than one atomicity,
and appear in different compounds with different
atomic values. The combinations of the
metals with the non-metallic elements may be
divided into two classes, those with chlorine,
iodine, bromine, and fluorine, and those with
oxygen, sulphur, selenium, and tellurium. The
former class are saline compounds, while the
latter are generally basic, exceptionally acid,
as before mentioned. Formerly the distinction
was generally observed between haloid and
oxygen salts, the former being the combination
of a metal with a haloid body, as chloride of
sodium, and the latter a combination of a basic
oxide with an oxy-acid, as sulphate of soda. In
the modern chemistry both characters of salts
are regarded as the replacements of hydrogen
in the acid by a metal. The combinations of
the metals among themselves are known as
alloys, or, in case of mercury, as amalgams.
(See Alloy, and Amalgam.)
