needs dollars, half-dollars, quarters, and dimes, notice is given and
offers are called for, stating the quantity for sale and its price.
When it is delivered, it is first of all "assayed"; that is, tested to
find out how nearly pure it is and how much it is worth. Next it is
refined, or purified from other metals, mixed with a little copper to
harden it, then melted again and poured into moulds to make bars. If
dollars are to be made, the bar is made thinner by passing it between
heavy rollers, and blanks for dollars are cut out with a die. These
blanks are weighed and every one that is too heavy or too light is put
back to be melted over again. Thus far these dollars are only round,
smooth pieces of metal. They must be milled to give them a rough edge,
and they must be stamped. For stamping, the piece of metal is placed
between two dies, one above and one below, and these close upon it
with a force of one hundred and fifty tons. Every part of the process
of manufacturing money is carried on with the utmost care. The places
where coins are made are called "mints." The United States has four;
the oldest is in Philadelphia, and there are branch mints in San
Francisco, New Orleans, and Denver. Coins minted in Philadelphia have
no distinguishing mark; but coins minted in San Francisco are marked
with a tiny "S"; if minted in New Orleans, with an "O"; and if in
Denver, with a "D."
VII
IRON, THE EVERYDAY METAL
Did you ever realize that your food and clothes, your books, and the
house in which you live all depend upon iron? Vegetables, grains, and
fruits are cultivated with iron tools; fish are caught with iron
hooks, and many iron articles are used in the care and sale of meat.
Clothes are woven on iron looms, sewed with iron needles, and fastened
together with buttons containing iron. Books are printed and bound by
iron machines, and sometimes written with iron pens or on iron
typewriters. Houses are put together with nails; and indeed, there is
hardly an article in use that could be made as well or as easily if
iron was not plenty. If you were making a world and wanted to give the
people the most useful metal possible, the gift would have to be iron;
and the wisest thing you could do would be to put it everywhere, but
in such forms that the people would have to use their brains to make
it of service.
This is just the way with the iron in our world. Wherever you see a
bank of red sand or red clay or a little brook which leaves a red mark
on the ground as it flows, there is iron. Iron is in most soils, in
red bricks, in garnets, in ripening apples, and even in your own
blood. It forms one twentieth part of the crust of the earth. Iron
dissolves in water if you give it time enough. If you leave a steel
tool out of doors on a wet night, it will rust; that is, some of the
iron will unite with the oxygen of the water. This is rather
inconvenient, and yet in another way this dissolving is a great
benefit. Through the millions of years that are past, the oxygen of
the rain has dissolved the iron in the hills and has worked it down,
so that now it is in great beds of ore or in rich "pockets" that are
often of generous size. One of them, which is now being mined in
Minnesota, is more than two miles long, half a mile wide, and of great
thickness. The rains are still at work washing down iron from the
hills. They carry the tiny particles along as easily as possible until
they come upon limestone. Then, almost as if it was frightened, the
brook drops its iron and runs away as fast as it can. Sometimes it
flows into a pond or bog in which are certain minute plants or animals
that act as limestone does, and the particles of iron fall to the
bottom of the pond. In colonial days much of the iron worked in
America was taken from these deposits. One kind of iron is of special
interest because it comes directly from the sky, and falls in the
shape of stones called "meteorites," some of which weigh many tons. In
some of the old fables about wonderful heroes, the stories sometimes
declare that the swords with which they accomplished their deeds of
prowess fell straight from the heavens, which probably means that they
were made of meteoric iron. Fortunately for the people and their
homes, meteorites are not common, but every large museum has
specimens of them.
It is not especially difficult to make iron if you have the ore, a
charcoal fire in a little oven of stones, and a pair of bellows. Put
on layers of charcoal alternating with layers of ore, blow the
bellows, and by and by you will have a lump of iron. It is not really
melted, but it can be pounded and worked. This is called the "Catalan
method," because the people of Catalonia in Spain made iron in this
way. It is still used by the natives of the interior of Africa. But if
all the iron was made by this method, it would be far more costly than
gold. The man who makes iron in these days must have an immense "blast
furnace," perhaps one hundred feet high, a real "pillar of fire." Into
this furnace are dropped masses of ore, and with it coke to make it
hotter and limestone to carry off the silica slag, or worthless part.
To increase the heat, blasts of hot air are blown into the bottom of
the furnace. This air is heated by passing it through great steel
cylinders as high as the furnace. The fuel used is nothing more than
the gases which come out at the top of the furnace.
The slag is so much lighter than iron that when the ore is melted the
slag floats on top just as oil floats on water, and can be drained out
of the furnace through a higher opening than that through which the
iron flows. The slag tap is open most of the time, but the iron tap is
opened only once in about six hours. It is a magnificent sight when a
furnace is "tapped" and the stream of iron drawn off. Imagine a great
shed, dark and gloomy, with many workmen hurrying about to make ready
for what is to come. The floor is of sand and slopes down from the
furnace. Through the center of this floor runs a long ditch straight
from the furnace to the end of the shed. Opening from it on both sides
are many smaller ditches; and connecting with these are little
gravelike depressions two or three feet long and as close together as
can be. These are called "pigs." When the time has come, the workmen
gather about the furnace, and with a long bar they drill into the
hard-baked clay of the tapping hole. Suddenly it breaks, and with a
rush and a roar the crimson flood of molten iron gushes out. It flows
down the trench into the ditches, then into the pigs, till their whole
pattern is marked out in glowing iron. Now the blast begins to drive
great beautiful sparks through the tapping hole. This means that the
molten iron is exhausted. The blast is turned off, and the "mud-gun"
is brought into position and shoots balls of clay into the tapping
hole to close it for another melting, or "drive." The crimson pigs
become rose-red, darken, and turn gray. The men play streams of water
over them and the building is filled with vapor. As soon as the pigs
are cool enough, they are carted away and piled up outside the
building.
In some iron works moulds of pressed steel carried on an endless chain
are used instead of sand floors. The chain carries them past the mouth
of a trough full of melted iron. They are filled, borne under water
to be cooled, and then dropped upon cars. A first-class machine can
make twenty pigs a minute.
[Illustration: IN THE STEEL FOUNDRY
It is a dangerous business to visit a steel mill. Tremendous kettles
travel overhead on huge cranes, hot metal flows from unexpected
places, and there is a constant glow and steam and roar everywhere to
confuse the unwary.]
Most of the iron made in blast furnaces is turned into steel. Steel
has been made for centuries, but until a few years ago the process was
slow and costly. A workman's steel tools were treasures, and a good
jackknife was a valuable article. Railroads were using iron rails.
They soon wore out, but at the suggestion to use steel, the presidents
of the roads would have exclaimed, "Steel, indeed! We might as well
use silver!" Trains needed to be longer and heavier, but iron rails
and bridges could not stand the strain. Land in cities was becoming
more valuable; higher buildings were needed, but stone was too
expensive. Everywhere there was a call for a metal that should be
strong and cheap. Iron was plentiful, but steel was dear. A cheaper
method of making iron into steel was needed; and whenever there is
pressing need of an invention, it is almost sure to come. Before long,
what is known as the "Bessemer process" was invented. One great
difficulty in the manufacture of steel was to leave just the right
amount of carbon in the iron. Bessemer simply took it all out, and
then put back exactly what was needed. Molten iron, tons and tons of
it, is run into an immense pear-shaped vessel called a "converter."
Fierce blasts of air are forced in from below. These unite with the
carbon and destroy it. There is a roar, a clatter, and a clang.
Terrible flames of glowing red shoot up. Suddenly they change from red
to yellow, then to white; and this is the signal that the carbon has
been burned out. The enormously heavy converter is so perfectly poised
that a child can move it. The workmen now tilt it and drop in whatever
carbon is needed. The molten steel is poured into square moulds,
forming masses called "blooms," and is carried away. More iron is put
into the converter, and the work begins again.
The Bessemer process makes enormous masses of steel and makes it very
cheaply; but it has one fault--it is too quick. The converter roars
away for a few minutes, till the carbon and other impurities are
burned out; and the men have no control over the operation. In what is
called the "open-hearth" process, pig iron, scrap iron, and ore are
melted together with whatever other substances may be needed to make
the particular kind of steel desired. This process takes much longer
than the Bessemer, but it can be controlled. Open-hearth steel is more
homogeneous,--that is, more nearly alike all the way through,--and is
better for some purposes, while for others the Bessemer is preferred.
Steel is hard and strong, but it has two faults. A steel bar will
stand a very heavy blow and not break, but if it is struck gently many
thousand times, it sometimes crystallizes and may snap. A steel rail
may carry a train for years and then may crystallize and break and
cause a wreck. Inventors are at work discovering alloys to prevent
this crystallization. The second fault of steel is that it rusts and
loses its strength. That is why an iron bridge or fence must be kept
painted to protect it from the moisture in the air.
If all the iron that is in use should suddenly disappear, did you ever
think what would happen? Houses, churches, skyscrapers, and bridges
would fall to the ground. Railroad trains, automobiles, and carriages
would become heaps of rubbish. Ships would fall apart and become only
scattered planks floating on the surface of the water. Clocks and
watches would become empty cases. There would be no machines for
manufacturing or for agriculture, not even a spade to dig a garden.
Everybody would be out of work. If you wish to see how it would seem,
try for an hour to use nothing that is of iron or has been made by
using iron.
VIII
OUR GOOD FRIEND COPPER
Where did rocks come from?
Some were deposited in water, like limestone and like the shale and
sandstone that lie over the strata of coal. Others were made by fire,
and were thrown up in a melted state from the interior of the earth.
Such rocks are the Giant's Causeway in Ireland and the Palisades of
the Hudson River. They are called "igneous" rocks, from the Latin word
_ignis_ meaning "fire."
When the igneous rocks were thrown up to the surface of the earth,
they brought various metals with them. How the metals happened to be
there ready to be brought up, no one knows. Some people think they
were dissolved in water and then deposited; others think that
electricity had something to do with their formation. However that may
be, metals were brought up with the igneous rocks, and one of these
metals is copper.
Now, to one who did not know how to work iron, copper was indeed a
wonderful treasure, for it made very good knives and spoons. The
people who lived in this country long before the Indians came
understood how to use it, and after a while the Indians themselves
found out its value. They did not trouble themselves to dig for it;
they simply picked it up from the ground, good pure metal in lumps;
and with stones for hammers they beat it into knives.
There was only one place in what is now the United States where they
could do this, and that was in northern Michigan. A long point of land
stretches out into Lake Superior as if it was trying to see what could
be found there. Just beyond its reach is Isle Royal; and in these two
places there was plenty of copper, enough for the Indians, enough for
the people who have come after them, and enough for a great many more.
One piece of copper which the Indians did not pick up, and the United
States Government did, is the famous Ontonagon Boulder, so called
because it was found near the Ontonagon River. It weighs more than
three tons. The Indians would have been glad to make use of it, but it
was too hard for their tools, and so they are said to have worshiped
it as a god. It is now in the National Museum in Washington.
The lumps of copper, such as those which delighted the hearts of the
Indians, are known to-day as "barrel" copper, because they are of a
good size to be dropped into barrels and carried away for smelting.
The great boulders which the Indians could not use are called "mass"
copper. Sometimes they weigh as much as five hundred tons. The copper
in them is almost pure, and a big boulder is worth perhaps $200,000.
Nevertheless, the mine-owners do not rejoice when they come upon such
a mass in their digging, for it cannot be either dug or blasted, and
has to be cut away with chisels of chilled steel. Now, a mine may be
wonderfully rich in metal, but if working it costs too much, then
another mine with less metal but more easily worked will pay better.
So it is with these great masses of copper. They are interesting to
study and they look well in museums, but they do not pay so well as
the "stamp" copper which is found in humble little bits in the gangue,
or the rock of the vein, and has to be pounded in a stamp mill. This
gangue is dug out and broken up as in mines of other metals. The
copper is much heavier than the rock, so it is easy to get rid of the
worthless gangue by means of a flow of water. The gangue of the
Michigan mines is exceedingly hard, but the stamps are so powerful
that one can crush five hundred tons in less than twenty-four hours.
Some copper can be taken out of the mortars at once, but the rest of
the broken gangue is fed to jigs, or screens, which are kept under
jets of water. The water is thrown up from below and the lighter rock
is tossed away, while the heavier copper falls through the tiny holes
in the screens.
[Illustration: IN A COPPER SMELTER
The men are pouring hot copper into moulds for castings.]
After the ore has been through all these experiences, it comes out
looking like dark-colored sand or coarse brown sugar. It is not
interesting, and no one who saw it for the first time would ever fancy
that it was going to turn into something beautiful. It is dumped into
freight cars and trundled off to the smelting furnaces. But however
uninteresting it looks, it is well worth while to follow these cars to
see what happens to it at the smelters. First of all, even before it
goes into the smelting furnace, it must be roasted. There is usually
sulphur combined with the copper, and roasting will get rid of much of
it. In some places this is done by building up a great heap of ore
with a little wood. The wood is kindled, and by the time it has burned
out, the sulphur in the ore has begun to burn, and in a good-sized
heap it will continue to burn for perhaps two months.
Such a heap is a good thing to keep away from, for the fumes of
sulphur are very disagreeable. Indeed, they will kill trees and other
growing things wherever the wind may carry them, even several miles
away. The managers of mines of copper as well as of gold and silver
have learned to economize; and it has been found that instead of
letting these fumes go into the air, they may be made to pass through
acid chambers lined with zinc and full of water. The water holds the
fumes, and can be used in making sulphuric acid.
After the ore has been roasted, it is put into the furnace for
smelting. If you should make an oven and put into it a mixture of wood
and roasted copper, that would be a smelting furnace. Set the wood on
fire, pump in air to make the flame hot, and if your furnace could be
made hot enough,--that is, 2300 deg. F., or about eleven times as hot as
boiling water,--you could smelt copper. Of course the furnace of a
real smelting factory will hold tons and tons of copper ore and has
all sorts of improvements, but after all it is in principle only an
oven with wood and ore and draft. Another sort of furnace, which is
better for some kinds of ore, has a grate for the fire and a bed above
it for the copper.
Imagine an enormous furnace holding between two and three hundred tons
of metal and burning with such a terrific heat that by contrast
boiling water would seem cool and comfortable. Suddenly, while you
stand looking at it, but a long way off, a door flies open and the
most beautiful cascade--only it is not a waterfall, but a _copper_
fall--pours out. It looks like red, red gold, rich and wonderful, with
little flames of red and blue dancing over it. It might almost be one
of the fire-breathing dragons of the old story-books; and if it should
get loose, it would devour whomever it touched far quicker than any
dragon. It hardly seems as if any one could manage such a monster; but
it looks easy, after you have seen it done. An enormous horizontal
wheel revolves slowly. On its edge are moulds shaped like bricks, but
much larger. On the hub of the wheel a workman sits to direct the
filling of these. A set of them is filled, and moves on, and others
take their place. When they are partly cooled, another workman, at the
farther side of the wheel, pries them out of the mould and drops them
into water. Then by the aid of the fingers of a machine and those of
men, they are loaded upon cars.
In copper there is often some gold and silver. The precious metals do
not make the copper any better, and if they can be separated from it,
they are well worth the trouble. This is done by electricity. It is so
successful that the metallurgists are hoping soon to take a long step
ahead and by means of electricity to produce refined copper directly
from the ore. Indeed, this has been done already in the laboratories,
but before the managers of mines can employ the method, a way of
making it less expensive must be discovered.
No mine that wastes anything is as well managed as it might be; and
superintendents are constantly on the watch for cheaper methods and
for ways to make the refuse matter of use. Even the scoria, or slag
from the furnaces, has been found to be good for something, and now it
is made into a coarse sort of brick that for certain rough uses is of
value. By the way, the shaft of a copper mine, the Red Jacket, has
shown itself of use in a manner that no one expected, namely, it helps
to prove that the earth turns around. This shaft is the deepest mining
shaft in the world, and when you get into the cage, you go down a full
mile toward the center of the earth. If you drop any article into the
shaft, it always strikes the east side before reaching the bottom. The
only way to explain this is that the earth turns toward the east.
Copper mixed with zinc forms brass, which is harder than copper alone.
It tarnishes, though not so easily as copper; but a coat of varnish
will protect it till the varnish wears off. A good way to find out the
many uses of brass and to see how valuable they are is to go along the
street and through a house and make a list. On the street you will see
signs, harness buckles, and buttons, everywhere. Look on the
automobiles and fire engines for a fine display of brass, polished and
shining. In the house you will find brass bedsteads, curtain rods,
faucets, pipes, drawerpulls, candlesticks, gas and electric fixtures,
lamps, the works of clocks and watches, and scores of other things.
You will not have any idea how many they are till you begin to count.
Copper mixed with tin forms bronze. Go into a hardware store and look
at the samples of bronze outside of each drawer, and you will be
surprised that there are so many. Bronze does not change even when in
the open air for ages. That is one reason why it has always been so
much used for statues. There are two strange facts about this mixture.
One is that bronze is harder than either copper or tin. The other is
that if you mix one pint of melted copper with one pint of tin, the
mixture will be less than a quart. Just why these things are so, no
one is quite certain. Mathematics declares that the whole is equal to
the sum of its parts; but in this one case the whole seems to be less
than the sum of its parts.
Another reason why bronze is so much used for statues is that the
castings are smooth. I once went to a foundry to have a brass ornament
shaped somewhat like a cone made for a clock. The foundryman formed a
mould in clay and poured the melted brass into it. When it had cooled,
the mould was broken off and the ornament taken out; but it was of no
use because it was so full of little hollows that it could not be made
smooth without cutting away a great deal of it. The man had to try
three times before he succeeded in making one that could be polished.
If it had been made of bronze, there would have been no trouble,
because bronze, hard as it is after it cools, flows when it is melted
almost as easily as molasses and fills every little nook and corner of
the mould.
A famous Latin poet named Horace, who lived two thousand years ago,
wrote of his poems, "I have reared a monument more lasting than
bronze"; and he was right, for few statues have endured from his day
to ours, but his poems are still read and admired.
Bells are made of bronze, about three quarters copper and one quarter
tin. It is thought that much copper gives a deep, full tone, and that
much tin with, sometimes, zinc makes the tone sharp. The age of a bell
has something to do with its sound being rich and mellow; but the
bellmaker has even more, for he must understand not only how to cast
it, but also how to tune it. If you tap a large bell, it will, if
properly tuned, sound a clear note. Tap it just on the curve of the
top, and it will give a note exactly one octave above the first. If
the note of the bell is too low, it can be made higher by cutting away
a little from the inner rim. If it is too high, it can be made lower
by filing on the inside a little above the rim. Many of the old bells
contain the gifts of silver and gold which were thrown in by people
who watched their founding. The most famous bell in the United States
is the "Liberty Bell" of Independence Hall, in Philadelphia, which
rang when Independence was adopted by Congress. This was founded in
England long before the Revolution and later was melted and founded
again in the United States.
It would not be easy to get on without brass and bronze; but even
these alloys are not so necessary as copper by itself. It is so strong
that it is used in boiler tubes of locomotives, as roofing for
buildings and railroad coaches, in the great pans and vats of the
sugar factories and refineries. A copper ore called "malachite," which
shows many shades of green, beautifully blended and mingled, is used
for the tops of tables. Wooden ships are often "copper-bottomed"; that
is, sheets of copper are nailed to that part of the hull which is
under water in order to prevent barnacles from making their homes on
it, and so lessening the speed of the vessel.