The first metal that was employed by man is copper. It is probable that
prehistoric man made use of the metal in its native condition only,
as no knowledge of metallurgy would be essential in preparing it for
use from that condition. Copper implements have been found in the lake
dwellings of Switzerland, and bronze, an alloy of copper and tin, is
mentioned in the writings of Homeric times.
Cuprum, the origin of our English word copper, is derived from cyprium,
which refers to the occurrence of the metal in especial abundance on
the island of Cyprus, the main source of the metal during the epochs
of early alchemy. In the Hebrew scriptures copper is termed Nehósheth
(from nahásh, meaning to glisten) which is translated by Χαλκος
and by Aes in the Vulgate. Later _Aes cyprium_ was the special
designation, which was finally shortened to _cyprium_, as indicated
above. Thus we see that our present term represents in no sense the
characteristic of the metal at first so noticeable.
Native copper scarcely needs a description. Its occurrence in the
free state provides an interesting subject of conjecture. Briefly
stated, the question of origin is whether the copper was set free by
the decomposition of silicates or was in the form of a sulphide in
the rock. The chief region of occurrence of native copper is the Lake
Superior district. Here are found occasionally large masses of copper,
which, strange as it seems, are practically valueless if too heavy to
transport, since they cannot be divided without great difficulty. Of
the world's total output of copper in 1897, 399,250 long tons[2], a
single mine of the Lake Superior region, the famous Calumet and Hecla,
produced 40,350 long tons.
Montana is now the first copper producing state in the United States.
The state contains the largest mining camp in the world, located in
the town of Butte. In 1897 the mines of Montana produced 102,800 long
tons of copper. The ore chalcocite, sometimes called copper glance,
has a metallic luster, often tarnished green or blue. It is commonly
lead-gray and rather soft. Its streak is a blackish lead-gray,
Chalcopyrite, a sulphide of copper and iron combined, has already
been mentioned under "Iron Minerals" (November issue of BIRDS AND ALL
NATURE.) When copper is much in predominance the color of the ore
is golden yellow. The streak is dark green. The mineral is harder
than chalcocite, but less hard than pyrite, being easily scratched
with a knife. Both chalcocite and chalcopyrite frequently occur in
silver-bearing rocks.
A method of extracting copper from its ores, equally useful with regard
to any of the ores, is known as the English process. The details of
this are too elaborate and technical for consideration here. In brief,
the process consists of six distinct parts--roasting the mixed ores,
fusion of the roasted ores to produce coarse metal, roasting the coarse
metal, fusion of the wasted coarse metal to produce what is known as
white metal, roasting of the white metal to produce blister copper,
i. e., copper filled with cavities, and finally the refining and
toughening of the blister copper until marketable copper is yielded.
The English method of copper smelting is classed among the so-called
"dry" processes, in contradistinction from "wet" processes, or methods
involving the use of solutions.
It may be of interest to know the importance of copper in that curious
problem of ancient alchemy, the transmutation of metals. Metallic
iron placed in certain solutions of unknown composition possessed the
power to precipitate metallic copper. With all the wondrous faith
in the problems of alchemy the phenomenon was interpreted as one of
transmutation and the statement made that iron had been transformed
into copper.
Within the last few years a remarkable increase in the output of the
copper mines of the world has been recorded. This is due mainly to
the demand for copper on account of the great strides in electrical
achievements during recent years. Yet there is no doubt that the
world's supply is wholly adequate to meet demands on it for a long
period to come. The high conductivity of copper renders it especially
useful for conveying electric currents and its most important use at
present is in electricity. However, it is also a common convenience
in many arts. Its alloys are numerous, bronze and brass being the
most common. Bronze is an alloy of copper and tin and brass of copper
and zinc. The manufacturer of bronze bells finds opportunity for an
interesting study of the alloy used in his product. The varying tones
of bells are due to the different percentages of copper and tin used in
the bell metal.
In locality and mode of occurrence lead is somewhat closely allied with
copper, and the ores of lead and zinc are almost invariably associated.
Hence a description of lead naturally follows that of copper and may
also be understood as typical, so far as occurrence and mining methods
are concerned, for that of zinc.
Lead occurs in nature chiefly in the forms of the sulphide, galenite
or galena, the sulphate, anglesite and the carbonate, cerussite.
Galena is lead-gray, quite soft, and frequently occurs in a coarsely
crystalline condition, the crystals often being cubical. The luster is
metallic, hence a superficial examination of a specimen might result
in mistaking the mineral for the copper ore, chalcopyrite, already
described. The streak will serve to identify any specimen, however,
it being a lead-gray of much lighter shade than that of chalcocite.
Anglesite and cerussite are far less abundant than galena. The former
varies from white through gray to yellow and has a resinous luster.
Cerussite is white or gray, resembling anglesite, and has a brilliant,
vitreous luster. Both minerals, like galena, are soft and easily
scratched with a knife.
The ores of lead are widely distributed throughout the United States
and it is difficult to assign boundaries to special districts.
Galena occurs in small quantities--too small for profitable
working--throughout the Appalachian region, and is found in paying
quantities in what is known as the Missouri lead district. In the
Colorado and other western mines the ore is found in silver-bearing
veins. Were it not for the presence of silver in those veins the
production of lead from them would probably practically cease, as the
anglesite, the principal lead ore of the veins, does not occur in
amount to pay for working the mines for that product alone.
White lead, used in paints, is the most important use of the metal.
Painters prefer the product to zinc-white chiefly because it is much
more opaque and possesses a much greater covering power. Much lead is
made into pipes for conveying water. Pure lead is not used for the
making of shot, but instead an alloy of lead and arsenic. Unlike pure
lead, the alloy assumes a spherical form when dropped through the
air. "Shot towers" are constructed to make use of this property in
the manufacture of shot. The demands for lead have not been increased
by recent extraordinary development of any of the arts employing the
metal, hence the world's output of lead during the past decade has had
a normal increase. For the year 1897 the total production of lead was
725,200 metric tons.
[Illustration: ORES.
Full size.
Chalcopyrite
Anglesite
Cerussite coating Galenite
Native Copper
Galenite
Chalcocite
CHICAGO:
A. W. MUMFORD, PUBLISHER.
COPYRIGHT 1900, BY
NATURE STUDY PUB. CO., CHICAGO.]
Footnote:
[2] The common short ton is 2,000 pounds; the long ton contains 2,240
pounds; the metric ton equals 2,204 pounds. It will be noted that
statistics of the production of different metals frequently employ
different tons as units.