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Title: Diggers in the Earth
Author: Eva March Tappan
Release Date: March 6, 2008 [EBook #24762]
Language: English
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THE INDUSTRIAL READERS
_Book II_
DIGGERS IN THE
EARTH
BY
EVA MARCH TAPPAN, Ph.D.
_Author of "England's Story," "American Hero Stories,"
"Old World Hero Stories," "Story of the Greek People,"
"Story of the Roman People," etc. Editor of
"The Children's Hour."_
[Illustration]
HOUGHTON MIFFLIN COMPANY
BOSTON NEW YORK CHICAGO
THE INDUSTRIAL READERS
By Eva March Tappan
I. THE FARMER AND HIS FRIENDS. 50 cents.
II. DIGGERS IN THE EARTH. 50 cents.
III. MAKERS OF MANY THINGS. 50 cents.
IV. TRAVELERS AND TRAVELING. 50 cents.
The foregoing are list prices, postpaid
COPYRIGHT, 1916, BY EVA MARCH TAPPAN
ALL RIGHTS RESERVED
_First printing April 1916;_
_Reprinted December 1916_
The Riverside Press
CAMBRIDGE, MASSACHUSETTS
U. S. A.
PREFACE
The four books of this series have been written not merely to provide
agreeable reading matter for children, but to give them information.
When a child can look at a steel pen not simply as an article
furnished by the city for his use, but rather as the result of many
interesting processes, he has made a distinct growth in intelligence.
When he has begun to apprehend the fruitfulness of the earth, both
above ground and below, and the best way in which its products may be
utilized and carried to the places where they are needed, he has not
only acquired a knowledge of many kinds of industrial life which may
help him to choose his life-work wisely from among them; but he has
learned the dependence of one person upon other persons, of one part
of the world upon other parts, and the necessity of peaceful
intercourse. Best of all, he has learned to see. Wordsworth's familiar
lines say of a man whose eyes had not been opened,--
"A primrose by a river's brim
A yellow primrose was to him,
And it was nothing more."
These books are planned to show the children that there is "something
more"; to broaden their horizon; to reveal to them what invention has
accomplished and what wide room for invention still remains; to teach
them that reward comes to the man who improves his output beyond the
task of the moment; and that success is waiting not for him who works
because he must, but him who works because he may.
Acknowledgment is due to the Lehigh Valley Railroad, Jones Brothers
Company, Alpha Portland Cement Company, Dwight W. Woodbridge, the Utah
Copper Company, the Aluminum Company of America, the Diamond Crystal
Salt Company, T. W. Rickard, and others, whose advice and criticism
have been of most valuable aid in the preparation of this volume.
EVA MARCH TAPPAN.
CONTENTS
I. IN A COAL MINE 1
II. DOWN IN THE QUARRIES 11
III. HOUSES OF SAND 21
IV. BRICKS, THEIR FAULTS AND THEIR VIRTUES 31
V. AT THE GOLD DIGGINGS 39
VI. THE STORY OF A SILVER MINE 48
VII. IRON, THE EVERYDAY METAL 57
VIII. OUR GOOD FRIEND COPPER 65
IX. THE NEW METAL, ALUMINUM 76
X. THE OIL IN OUR LAMPS 84
XI. LITTLE GRAINS OF SALT 95
LIST OF ILLUSTRATIONS
A STRUCTURAL STEEL APARTMENT BUILDING vi
HOW A COAL MINE LOOKS ABOVEGROUND 5
MINERS AND THEIR MINE 10
OPENING A GRANITE QUARRY 13
BUILDING A CONCRETE ROAD 27
IN A NEW JERSEY BRICK MILL 33
HYDRAULIC GOLD MINING 41
THE STORY OF A SPOON 51
IN THE STEEL FOUNDRY 61
IN A COPPER SMELTER 67
A "MOVIE" OF AN ALUMINUM FUNNEL 79
A CALIFORNIA OIL FIELD 87
[Illustration: A STRUCTURAL STEEL APARTMENT BUILDING
_Courtesy American Bridge Co._
First the steel frame, then the floors, then the stone or brick shell,
then the interior finishing--this is how the building is made.]
THE INDUSTRIAL READERS
BOOK II
DIGGERS IN THE EARTH
I
IN A COAL MINE
Did you ever wonder how beds of coal happened to be in the earth? This
is their story.
Centuries ago, so many thousand centuries that even the most learned
men can only guess at their number, strange things were coming to
pass. The air was so moist and cloudy that the sun's rays had hard
work to get through. It was warm, nevertheless, for the crust of the
earth was not nearly so thick as it is now, and much heat came from
the earth itself. Many plants and trees grow best in warm, moist air;
and such plants flourished in those days. Some of their descendants
are living now, but they are dwarfs, while their ancestors were
giants. There is a little "horse-tail" growing in our meadows, and
there are ferns and club mosses almost everywhere. These are some of
the descendants; but many of their ancestors were forty or fifty feet
high. They grew very fast, especially in swamps; and when they died,
there was no lack of others to take their places. Dead leaves fell and
heaped up around them. Stumps stood and decayed, just as they do in
our forests to-day. Every year the soft, black, decaying mass grew
deeper. As the crust of the earth was so thin, it bent and wrinkled
easily. It often sank in one place and rose in another. When these
low, swampy places sank, water rushed over them, pressing down upon
them with a great weight and sweeping in sand and clay. Now, if you
burn a heap of wood in the open air, the carbon in the wood burns and
only a pile of ashes remains. "Burning" means that the carbon in the
wood unites with the oxygen gas in the air. If you cover the wood
before you light it, so that only a little oxygen reaches it, much of
the carbon is left, in the form of charcoal.
When wood decays, its carbon unites with the oxygen of the air; and so
decay is really a sort of burning. In the forests of to-day the
leaves, and at length the trees themselves, fall and decay in the open
air; but at the time when our coal was forming, the water kept the air
away, and much carbon was left. This is the way coal was made. Some of
the layers, or strata, are fifty or sixty feet thick, and some are
hardly thicker than paper. On top of each one is a stratum of
sandstone or dark-gray shale. This was made by the sand and mud which
were brought in by the water. These shaly rocks split easily into
sheets and show beautiful fossil impressions of ferns. There are also
impressions of the bark and fruit of trees, together with shells,
crinoids, corals, remains of fishes and flying lizards, and some few
trilobites,--crablike animals with a shell somewhat like the back of
a lobster, but marked into three divisions or lobes, from which its
name comes.
Since the crust of the earth was so thin and yielding, it wrinkled up
as the earth cooled, much as the skin of an apple wrinkles when the
apple dries. This brought some of the strata of coal to the surface,
and after a while people discovered that it would burn. If a vein of
coal cropped out on a man's farm, he broke some of it up with his
pickaxe, shoveled it into his wheelbarrow, and wheeled it home. After
a while hundreds of thousands of people wanted coal; and now it had to
be mined. In some places the coal stratum was horizontal and cropped
out on the side of a hill, so that a level road could be dug straight
into it. In other places the coal was so near the surface that it
could be quarried under the open sky, just as granite is quarried.
Generally, however, if you wish to visit a coal mine, you go to a
shaft, a square, black well sometimes deeper than the height of three
or four ordinary church steeples. You get into the "cage," a great
steel box, and are lowered down, down, down. At last the cage stops
and you are at the bottom of the mine. The miners' faces, hands,
overalls, are all black with coal dust. They wear tiny lamps on their
caps, and as they come near the walls of coal, it sparkles as it
catches the light. Here and there hangs an electric lamp. It is doing
its best to give out light, but its glass is thick with coal dust. The
low roof is held up by stout wooden timbers and pillars of coal. A
long passageway stretches off into a blacker darkness than you ever
dreamed of. Suddenly there is a blaze of red light far down the
passage, a roar, a medley of all sorts of noises,--the rattling of
chains, the clattering of couplings, the shouts of men, the crash of
coal falling into the bins. It is a locomotive dragging its line of
cars loaded with coal. In a few minutes it rushes back with empty cars
to have them refilled.
All along this passageway are "rooms," that is, chambers which have
been made by digging out the coal. Above them is a vast amount of
earth and rock, sometimes hundreds of feet in thickness. There is
always danger that the roof will cave in, and so the rooms are not
made large, and great pillars of coal are left to hold up the roof.
Not many years ago the miner used to do all the work with his muscles;
now machines do most of it. The miner then had to lie down on his side
near the wall of coal in his "room" and cut into it, close to the
floor, as far as his pickaxe would reach. Then he bored a hole into
the top of the coal, pushed in a cartridge, thrust in a slender squib,
lighted it, and ran for his life. The cartridge exploded, and perhaps
a ton or two of coal fell. The miner's helper shoveled this into a car
and pushed it out of the room to join the long string of cars.
[Illustration: HOW A COAL MINE LOOKS ABOVEGROUND
All that shows on the surface is the machinery shed where the various
engines work to keep the air fresh, and bring up the miners and the
coal.]
That is the way mining used to be done. In these days a man with a
small machine for cutting coal comes first. He puts his cutter on the
floor against the wall of coal and turns on the electricity. _Chip,
chip_, grinds the machine, eating its way swiftly into the coal, and
soon there is a deep cut all along the side of the room. The man and
his machine go elsewhere, and the first room is left for its next
visitors. They come in the evening and bore holes for the blasting.
Once these holes were bored by hand, but now they are made with
powerful drills that work by compressed air. A little later other men
come and set off cartridges. In the morning when the dust has settled
and the smoke has blown away, the loaders appear with their shovels
and load the coal into the cars. Then it is raised to the surface and
made ready for market.
Did you ever notice that some pieces of coal are dull and smutty,
while others are hard and bright? The dull coal is called bituminous,
because it contains more bitumen or mineral pitch. This is often sold
as "run-of-mine" coal,--that is, just as it comes from the mine,
whether in big pieces or in little ones; but sometimes it is passed
over screens, and in this process the dust and smaller bits drop out.
The second kind of coal, the sort that is hard and bright, is
anthracite. Its name is connected with a Greek word meaning ruby. It
burns with a glow, but does not blaze. Most of the anthracite coal is
used in houses, and householders will not buy it unless the pieces are
of nearly the same size and free from dirt, coal dust, and slate. The
work of preparation is done in odd-shaped buildings called "breakers."
One part of a breaker is often a hundred or a hundred and fifty feet
in height. The coal is carried to the top of the breaker. From there
it makes a journey to the ground, but something happens to it every
little way. It goes between rollers, which crush it; then over
screens, through which the smaller pieces fall. Sometimes the screens
are so made that the coal will pass over them, while the thin, flat
pieces of slate will fall through. In spite of all this, bits of coal
mixed with slate sometimes slide down with the coal, and these are
picked out by boys. A better way of getting rid of them is now coming
into use. This is to put the coal and slate into moving water. The
slate is heavier than the coal, and sinks; and so the coal can easily
be separated from it. Dealers have names for the various sizes of
coal. "Egg" must be between two and two and five eighths inches in
diameter; "nut" between three fourths and one and one eighth inches;
"pea" between one half and three fourths of an inch.
Mining coal is dangerous work. Any blow of the pickaxe may break into
a vein of water which will burst out and flood the mine. The wooden
props which support the roof may break, or the pillars of coal may not
be large enough; and the roof may fall in and crush the workers. There
are always poisonous gases. The coal, as has been said before, was
made under water, and therefore the gas which was formed in the
decaying leaves and wood could not escape. It is always bubbling out
from the coal, and at any moment a pickaxe may break into a hole that
is full of it. One kind of gas is called "choke-damp," because it
chokes or suffocates any one who breathes it. There is also
"white-damp," the gas which you see burning with a pretty blue flame
over a hot coal fire. Worst of all is the "fire-damp." If you stir up
the water in a marsh, you will see bubbles of it rise to the surface.
It is harmless in a marsh, but quite the opposite in a mine. When it
unites with a certain amount of air, it becomes explosive, and the
least bit of flame will cause a terrible explosion. Even coal dust may
explode if the air is full of it, and it is suddenly set in motion by
too heavy a blast of powder.
Miners used to work by candlelight. Every one knew how dangerous this
was; but no one found any better way until, about a hundred years ago,
Sir Humphry Davy noticed something which other people had not
observed. He discovered that flame would not pass through fine wire
gauze, and he made a safety lamp in which a little oil lamp was placed
in a round funnel of wire gauze. The light, but not the flame, would
pass through it; and all safety lamps that burn oil have been made on
this principle. The electric lamp, however, is now in general use. The
miner wears it on his cap, and between his shoulders he carries a
small, light storage battery. Even with safety lamps, however, there
are sometimes explosions. The only way to make a mine at all safe from
dangerous gases is to keep it full of fresh, pure air. There is no
wind to blow through the chambers and passages, and therefore air has
to be forced in. One way is to keep a large fire at the bottom of the
air shaft. If you stand on a stepladder, you will feel that the top of
the room is much warmer than the floor. This is because hot air
rises; and in a mine, the hot air over the fire rises and sucks the
foul air and gas out of the mine, and fresh air rushes in to take its
place. Another way is by a "fan," a machine that forces fresh air into
the mine.
[Illustration: MINERS AND THEIR MINE
Notice the safety lamps in the men's caps, and the little railroad on
which the cars of coal and ore travel, hauled by the useful mule.]
So it is that by hard work and much danger we get coal for burning.
Now, coal is dirty and heavy. A coal fire is hard to kindle and hard
to put out, and the ashes are decidedly disagreeable to handle. And
after all, we do not really burn the coal itself, but only the gas
from it which results from the union of carbon and oxygen. In some
places natural gas, as it is called, which comes directly from some
storehouse in the ground, is used in stoves and furnaces and
fireplaces for both heating and cooking; and perhaps before long gas
will be manufactured so cheaply and can be used so safely and
comfortably that we shall not have to burn coal at all, but can use
gas for all purposes--unless electricity should take its place.
II
DOWN IN THE QUARRIES
When walking in the country one day I came to a beautiful pond by the
side of the road. The water was almost as clear as air, and as I
looked down into it, I could see that the bottom was made of granite.
The farther shores were cliffs of clean granite thirty or forty feet
high and coming down to the water's edge. The marks of tools could be
seen on them, showing where blocks of stone had evidently been split
off. I picked up a piece of the rock and examined it closely. It
proved to be made up of three kinds of material. First, there were
tiny sparkling bits of mica. In some places there are mica mines
yielding big sheets of this curious mineral which is used in the doors
of stoves and the little windows of automobile curtains. With the
point of a knife the bits in my piece of granite could be split into
tiny sheets as thin as paper. The second material was quartz. This was
grayish-white and looked somewhat like glass. The third material was
feldspar. This, too, was whitish, but one or two sides of each bit
were flat, as if they had not been broken, but split. This is the most
common kind of granite. There are many varieties. Some of them are
almost white, some dark gray, others pale pink, and yet others deep
red. It is found in more than half the States of the Union.
This quarry had been given up and allowed to fill with water; but it
was a granite country, and farther down the road there was another,
where scores of men were hard at work. This second quarry was part-way
up a hill; or rather, it was a hill of granite which men were digging
out and carrying away. When they began to open the quarry, much of the
rock was covered with dirt and loose stones, and even the granite that
showed aboveground was worn and broken and stained. This is called
"trap rock." The easiest way to get rid of it is to blast with
dynamite and then carry away the dirt and fragments. Next comes the
getting out of great masses of rock to use, some of them perhaps long
enough to make the pillars of a large building.
[Illustration: OPENING A GRANITE QUARRY
_Courtesy Jones Brothers Company._
The first thing to do is to strip off the soil from the stone. Then,
as the blocks are cut out, the big derrick lifts and loads them on
waiting cars.]
Now, granite is a hard stone, but there is no special difficulty in
cutting it if you know how. In the old days, when people wished to
split a big boulder, they sometimes built a fire beside it, and when
it was well heated, they dropped a heavy iron ball upon it. King's
Chapel in Boston was built of stone broken in this way. To break from
a cliff, however, a block of granite big enough to make a long pillar
is a different matter, and this is what the men were doing. First of
all, the foreman had examined the quarry till he had found a stratum
of the right thickness. He had marked where the ends were to come, and
the men had drilled holes down to the bottom of the stratum. Then he
had drawn a line at the back along where he wished the split to be,
and the men had drilled on this line also a row of holes. Next came
the blasting. If one very heavy charge had been exploded, it would
probably have shattered the whole mass, or at any rate have injured it
badly. Instead of this, they put into each hole a light charge of
coarse powder and covered it with sand. These were all fired at the
same instant, and thus the great block was loosened from the wall.
Sometimes there seems to be no sign of strata, and then a line of
horizontal holes must be drilled where the bottom of the block is to
be. After this comes what is called the "plug-and-feather" process.
Into each hole are placed two pieces of iron, shaped like a pencil
split down the middle. These are the "feathers." The "plug" is a small
steel wedge that is put between the iron pieces. Then two men with
hammers go down the line and strike each wedge almost as gently as if
it was a nut whose kernel they were afraid of crushing. They go down
the line again, striking as softly as before. Then, if you look
closely, you can see a tiny crack between the holes. There is more
hammering, the crack stretches farther, a few of the wedges are driven
deeper and the others drop out. The block splits off. A mighty chain
is then wound about it, the steam derrick lifts it, lays it gently
upon a car, and it is carried to the shed to be cut into shape,
smoothed, and perhaps polished.
In almost every kind of work new methods are invented after a while.
In quarrying, however, the same old methods are in use. The only
difference is that, instead of the work being done by muscle, it is
done by compressed air or steam or electricity. Compressed air or
steam works the drill and the sledgehammer. The drill is held by an
arm, but the arm is a long steel rod which is only guided by the
workman. Not the horse-sweep of old times, but the steam derrick and
the electric hoist lift the heavy blocks from the quarry. Polishing
used to be a very slow, expensive operation, because it was all done
by the strength of some one's right arm, but now, although it takes as
much work as ever, this work is done by machinery. To "point" a piece
of stone, or give it a somewhat smooth surface, is done now with tools
worked by compressed air. After this, the stone is rubbed--by
machinery, of course--with water and emery, then by wet felt covered
with pumice or polishing putty. A few years ago two young Vermonters
invented a machine that would saw granite. This saw has no teeth, but
only blades of iron. Between these blades and the piece of granite,
however, shot of chilled steel are poured; and they do the real
cutting.
Granite has long been used in building wherever a strong, solid
material was needed; but until the sand blast was tried, people
thought it impossible to do fine work in this stone. There was a firm
in Vermont, however, who believed in the sand blast. They had a
contract with the Government to furnish several thousand headstones
for national cemeteries. Cutting the names would be slow and costly;
so they made letters and figures of iron, stuck them to the stones,
and turned on the blast. If a sand blast is only fast enough, it will
cut stone harder than itself. The blast was turned upon a stone for
five minutes. Then the iron letters were removed. There stood in
raised letters the name, company, regiment, and rank of the soldier,
while a quarter of an inch of the rest of the stone, which the iron
letters had not protected, had been cut away. By means of the sand
blast it has become possible to do beautiful carving even in material
as hard as granite.
Granite looks so solid that people used to think it was fireproof; but
it is really poor material in a great fire. Most substances expand
when they are heated; but the three substances of which granite is
made do not expand alike, and so they tend to break apart and the
granite crumbles.
A marble quarry is even more interesting than a granite quarry. If you
stand on a hill in a part of the country where marble is worked, you
will see white ledges cropping out here and there. The little villages
are white because many of the houses are built of marble. Then, too,
there are great marble quarries flashing in the sunshine. Sometimes a
marble quarry is chiefly on the surface. Sometimes the marble
stretches into the earth, and the cutting follows it until a great
cavern is made, perhaps two or three hundred feet deep. A roof is
often built to keep out the rain and snow. It keeps out the light,
too, and on rainy days the roof, together with the smoke and steam of
the engines, makes the bottom of the quarry a gloomy place. Everywhere
there are slender ladders with men running up and down them. There
are shouts of the men, clanking of chains, and puffing of locomotives.
Marble is cut out in somewhat the same way as granite, but a valuable
machine called a "channeler" is much used. This machine runs back and
forth, cutting a channel two inches wide along the ends and back and
sometimes the bottom of the block to be taken out.
Marble is so much softer than granite that it is far more easy to
work. Cutting it is a simple matter. The saw, which is a smooth flat
blade of iron, swings back and forth, while between it and the marble
sand and water are fed. It does not exactly _cut_, but rubs, its way
through. The round holes in the tops of washstands are cut by saws
like this, only bent in the form of a cylinder and turned round and
round, going in a little deeper at each revolution. A queer sort of
saw is coming into use. It is a cord made of three steel wires twisted
loosely together. This cord is stretched tightly over pulleys and
moves very rapidly. Every little ridge of the cord strikes the stone
and cuts a little of it away.
There are varieties of marble without end. The purest and daintiest is
the white of which statues are carved; but there are black, red,
yellow, gray, blue, green, pink, and orange in all shades. Many are
beautifully marked. The inner walls of buildings are sometimes covered
with thin slabs of marble. These are often carefully split, and the
two pieces put up side by side, so that the pattern on one is reversed
on the other. Certain kinds of marble contain fossils or remains of
coral and other animals that lived hundreds of thousands of years ago.
In some marbles there are so many that the stone seems to be almost
made of them. When a slab is cut and polished, the fossils are of
course cut into; but even then we can sometimes see their shape. One
of the most common is the crinoid. This was really an animal, but it
looked somewhat like a closed pond lily with a long stem, and people
used to call it the stone lily. This stem is made up of little flat
rings looking like bits of a pipestem. The stems are often broken up
and these bits are scattered through the marble. The animals whose
shells help to make marble lived in the ocean, and when they died sank
to the bottom. Many of the shells were broken by the beating of the
waves, but both broken shells and whole ones became united and
hardened into limestone, one kind of which we call marble. Common
chalk is another kind. Blackboard crayons are made of this: so are
whitewash and whiting for cleaning silver and making putty.
Another stone that builders would be sorry to do without is slate.
This, too, was formed at the bottom of the sea. Rivers brought down
fine particles of clay, which settled, were covered by other matter,
and finally became stone. It was formed in layers, of course, but,
queerly enough, it splits at right angles to its bottom line. Just why
it does this is not quite certain, but the action is thought to be due
to heat and long, slow pressure, which will do wonderful things, as in
the case of coal. This splitting is a great convenience for the
people who want to use it for roofing and for blackboards. Blocks of
slate are loosened by blasting, and are taken to the splitting-shed.
Splitting slate needs care, and a man who is not careful should never
try to work in a slate quarry. The splitting begins by one man's
dividing the block into pieces about two inches thick and somewhat
larger than the slates are to be when finished. The way he does this
is to cut a little notch in one end of the block with his "sculpin
chisel" and make a groove from this across the block. He must then set
his chisel into the groove, strike it with a mallet, and split the
slate to the bottom. This sounds easy, but it needs skill. Slate has
sometimes its own notions of behavior, and it does not always care to
split in a straight line exactly perpendicular to the bottom of the
stratum. The man keeps it wet so that he can see the crack more
plainly, and if that crack turns back a little to the right, he must
turn it to the left by striking the sculpin toward the left, or
perhaps by striking a rather heavy blow on the left of the stone
itself. Now the chief splitter takes it, and with a broad thin chisel
he splits it into plates becoming thinner at each split. The second
assistant trims these into the proper shape and size with either a
heavy knife or a machine. Slate can be sawed and planed; but whatever
is done to it should be done when it first comes from the quarry, for
then it is not so likely to break. It would be very much cheaper if so
much was not broken and wasted at the quarries and in the splitting.
It is said that in Wales sometimes one hundred tons of stone are
broken up to get between three and four tons of good slate. Within the
last few years the quarrymen have been using channeling machines and
getting out the slate in great masses instead of small blocks. This is
not so wasteful by any means; but even now there is room for new and
helpful inventions.
III
HOUSES OF SAND
If you wanted to build a house, of what should you build it? In a new
country, people generally use wood; but after a time wood grows
expensive. Moreover, wood catches fire easily; therefore, as a country
becomes more thickly settled and people live close together in cities,
stone and brick are used. Large cities do not allow the building of
wooden houses within a certain distance from the center, and sometimes
even the use of wooden shingles is forbidden. Of late years large
numbers of "concrete" or "cement" houses have been built. Our
grandfathers would have opened their eyes wide at the suggestion of a
house built of sand, and would have felt anxious at every rainfall
lest their homes should suddenly melt away. Even after thousands of
concrete buildings were in use, many people still feared that they
would not stand the cold winters and hot summers of the United States;
but it has been proved that concrete is a success provided it is
properly made.
No one can succeed in any work unless he understands how it should be
done. Concrete is made of Portland cement, mixed with sand and water
and either broken stone, gravel, cinders, or slag; but if any one
thinks that he can mix these together without knowing how and produce
good concrete, he will make a bad mistake rather than a good building
material.
First, he must buy Portland cement of the best quality. This cement is
made of limestone and clay, or marl, chalk, and slag. These are
crushed and ground and put into a kiln which is heated up to 2500° or
3000°F.; that is, from twelve to fourteen times as hot as boiling
water. The stone fuses sufficiently to form a sort of clinker. After
this has cooled, it is ground so fine that the greater part of it will
pass through a sieve having 40,000 meshes to the square inch. To every
hundred pounds of this powder, about three pounds of gypsum is added.
The mixture is then put into the bags in which we see it for sale in
the stores. This powder is so greedy for water that it will absorb the
moisture from the air around it. Even in the bags, it begins to harden
as soon as it gets some moisture; and as soon as it hardens, it is of
no use. The moral of that is to keep your cement in a dry place.
The second substance needed in concrete is broken stone or gravel. Of
course a hard rock must be selected, such as granite or trap rock.
Limestone calcines in a heat exceeding 1000° F., and therefore it
cannot be used in fireproof construction. Soft rock, like slate or
shale or soft sandstone, will not answer because it is not strong
enough. Gravel is always hard. If you look at a cut in a gravel bank,
you will usually see strata of sand and then strata of rounded pebbles
of different sizes. The sand was once an ancient sea beach; the
pebbles were dashed up on it by waves or storms or some change of
currents. They were at first only broken bits of rock, but after being
rolled about for a few thousand years in the ocean and on the shore,
the corners were all rounded. Soft rock would have been ground to
powder by such treatment. Sometimes, if there is to be no great strain
on the concrete, cinders or pieces of brick may be used instead of
stone; and for some purposes they answer very well.
The third substance used in concrete is sand; but it must be the right
kind of sand, having both fine and coarse grains. These grains need to
be sharp, or the cement will not stick to them well. They must also be
clean, that is, free from dirt. If you rub sand between your hands,
and it soils them, then there is clay or loam with it, and it must not
be used in making concrete unless it is thoroughly washed. Another way
of testing it is to put it into a glass jar partly full of water and
shake it. Then let it settle. If there is soil in the sand, it will
appear as a stratum of mud on top of the sand.
The water with which these three substances are to be mixed must be
clean and must contain no acid and no strong alkali. As a general
rule, there must be twice as much broken stone as sand. When people
first make concrete, they often expect too much of their materials. A
good rule for the strongest sort of cement, strong enough for floors
on which heavy machines are to stand, is one fourth of a barrel of
cement, half a barrel of sand, and one barrel of gravel or broken
stone. Apparently this would make one and three fourths barrels; but
in reality it makes only about one barrel, because the sand fills in
the spaces between the gravel, and the cement fills in the spaces
between the grains of sand.
There are many sorts of machines on the market for mixing the
materials; but small quantities can just as well be mixed by hand. The
"mixing-bowl" is a platform, and on this the sand is laid. Then comes
the cement; and these two must be shoveled together several times.
While this is being done, the broken stone or gravel must be wet, and
now it is put on top of the sand and cement and well shoveled
together, with just enough water added so that the mass will almost
bear the weight of a man.
Concrete is impatient to be hardening, and if it is not put into the
right place, it will begin promptly to harden in the wrong place, and
nothing can be done with it afterwards. If it is to be made in blocks,
the moulds must be ready and the concrete put into them at once and
well tamped down. For such uses as beams and the sides of tanks where
great strength is needed, the cement is often "reinforced," that is,
rods of iron or steel are embedded in it. For floors, a sheet of woven
wire is often stretched out and embedded. At first only solid blocks,
made to imitate rough stone, were used for houses, but the hollow
block soon took their place. This is cheaper; houses built this way
are warmer in winter and cooler in summer; and it prevents moisture
from working through the walls. Many cities have regulations about the
use of hollow blocks, all the more strict because concrete is
comparatively new as a building material. In Philadelphia the blocks
must be composed of at least one barrel of Portland cement to five
barrels of crushed rock or gravel. They must be three weeks old or
more before being used; the lintels and sills of the doors must be
reinforced; and every block must be marked, so that if the building
should not prove to be of proper strength, the maker may be known.
There would seem, however, to be little question of the quality of the
blocks, for samples must pass the tests of the Bureau of Building
Inspection.
Even better than the hollow block is the method of making the four
walls of a house at once by building double walls of boards and
pouring in the concrete. When this has hardened, the boards are
removed, and whatever sort of finish the owner prefers is given to the
walls. They can be treated by spatter-work, pebble dash, or in other
ways before the cement is fully set, or by bush hammering and tool
work after the cement has hardened. Coloring matter can be mixed with
the cement in the first place; and if the owner decides to change the
color after the house is completed, he can paint it with a thin cement
of coloring matter mixed with plaster of Paris.
A concrete house has several advantages. In the first place, it will
not burn. Neither will granite, but granite will fall to pieces in a
hot fire. Granite is made of quartz, mica, and feldspar, as has been
said before. These three do not expand alike in heat; and therefore
great flakes of the stone split off, so that it really seems to melt
away. A well-made concrete is not affected by fire. It will not burn,
and it will not carry heat to make other things burn. For a concrete
house no paint is needed and less fuel will be required to keep it
warm. If the floors are made with even a very little slant,
"house-cleaning" consists of removing the furniture and turning on the
hose. Water-tank, sink, washtubs, and bathtubs can be cast in concrete
and given a smooth finish. Wooden floors can be laid over the
concrete, or a border of wood can be put around each room for tacking
down carpets or rugs. A concrete house may be as ornamental as the
owner chooses, for columns and cornices and mouldings can easily be
made of concrete; and if they are cast in sand, as iron is, they will
have a finish like sandstone.
It is somewhat troublesome to lay concrete in very cold weather,
because of the danger of freezing and cracking. Sometimes the
materials are heated, and after the concrete is in place, straw or
sand or sawdust is spread over it. These will keep it warm for several
hours, and so give the concrete a chance to "set." Sometimes a canvas
house is built over the work. When a concrete dam was to be built in
the Province of Quebec and the mercury was 20° below zero, the
contractors built a canvas house over one portion of the dam and set
up iron stoves in it. When this part was completed, they took down the
house and built it up again over another portion of the dam.
Sometimes salt is used. Salt water is heavier than fresh water and
will not freeze so easily. Therefore salt put into the water used in
making the concrete will enable it to endure more cold without
freezing; but not more than one pound of salt to twelve gallons of
water should be used.
[Illustration: BUILDING A CONCRETE ROAD
_Courtesy Alpha Portland Cement Co._
The concrete mixer travels along the prepared roadbed, and after it
follow the workmen with levelers and stamps.]
Concrete objects to being frozen before it is "set," but it is
exceedingly accommodating about working under water. It must, of
course, be carried in some way through the water to its proper place
without being washed away, but this is easily done. Sometimes it is
let down in great buckets closed at the top, but with a hinged bottom
that will open when the bucket strikes the rock or soil where the
material is to be left. Sometimes it is poured down through a tube.
Sometimes it is dropped in sacks made of cloth. This cloth must be
coarse, so that enough of the concrete will ooze through it to unite
the bag and its contents with what is below it and make a solid mass.
Sometimes even paper bags have been successfully used. The concrete,
made rather dry, is poured into the bags and they are slid down a
chute. The paper soon becomes soft and breaks, and lets the concrete
out. Sometimes concrete blocks are moulded on land and lowered by a
derrick, while a diver stands ready to see that they go into their
proper places.
Concrete is used for houses, churches, factories, walls, sidewalks,
steps, foundations, sewers, chimneys, piers, cellar bottoms, cisterns,
tunnels, and even bridges. In the country, it is used for silos, barn
floors, ice houses, bins for vegetables, box stalls for horses,
doghouses, henhouses, fence posts, and drinking-troughs. It is of very
great value in filling cavities in decaying trees. All the decayed
wood must be cut out, and some long nails driven from within the
cavity part-way toward the outside, so as to help hold the concrete.
Then it is poured in and allowed to harden. If the cavity is so large
that there is danger of the trunk's breaking, an iron pipe may be set
in to strengthen it. If this is encased in concrete, it will not rust.
A horizontal limb with a large cavity may be strengthened by bending a
piece of piping and running one part of it into the limb and the other
into the trunk, then filling the whole cavity with concrete. If the
bark is trimmed in such a way as to slant in toward the cavity, it
will sometimes grow entirely over it.
Concrete is also used for stucco work, that is, for plastering the
outside of buildings. If the building to be stuccoed is of brick or
stone, the only preparation needed is to clean it and wet it; then put
on the plaster between one and two inches thick. A wooden house must
first be covered with two thicknesses of roofing-paper, then by wire
lathing. The concrete will squeeze through the lathing and set. Stucco
work is nothing new, and if it is well done, it is lasting.
Concrete has been used for many purposes besides building, and the
number of purposes increases rapidly. For blackboards, refrigerator
linings, and railroad ties it has been found available, and for poles
or posts of all sizes it has already proved itself a success. It has
even been suggested as an excellent material for boats, if reinforced;
and minute directions are given by one writer for making a concrete
rowboat. To do this, the wooden boat to be copied is hung up just
above the ground, and clay built around it, leaving a space between
boat and clay as thick as the concrete boat is to be. The wooden boat
is covered with paper and greased, then the concrete is poured into
the space between the boat and the clay mould; and when it hardens and
the wooden boat is removed, there is a boat of stone--or so the
directions declare; but I think most people would prefer one of wood.
However it may be with rowboats, concrete is taking an important place
in the construction of battleships, a backing for armor being made of
it instead of teakwood. The Arizona is built in this way.
Concrete that is carelessly made is very poor stuff, and dangerous to
use, for it is not at all reliable and may give out at any time; but
concrete that is made of the best materials and properly put together
is an exceedingly valuable article.
IV
BRICKS, THEIR FAULTS AND THEIR VIRTUES
The simplest way to make a brick is to fill a mould with soft clay,
then take it out and let it stiffen, and then put it in the sun to
dry. This is the way in which the "adobe" bricks of Central America
are made. They answer very well in countries where there is little
rain; but one or two heavy downpours would be likely to melt a house
built of such material.
Clay is a kind of earth containing mostly alumina and silica or sand,
that can be mixed with water, moulded into any shape, retain that
shape after it is dry, and become hard by being burned. If you want to
make a china cup, you must have a fine sort of clay called "kaolin,"
which is pure white when it is fired and is not very common; but if
you want to make bricks, it will not be at all difficult to find a
suitable clay bank. And yet the clay, even for bricks, must be of the
right kind. If it contains too much silica (sand), the brick will not
mould well; if too much alumina it will be weak; if too much iron, it
will lose its shape in burning; if too much lime, it will be
flesh-colored when it is burned.
If you want to find out whether a building-brick is of good quality,
there are some tests that a boy or girl can apply as well as any one.
First, look the brick over and note whether it is straight and true,
and whether the edges and corners are sharp. Strike it, and see
whether it gives a clear, ringing sound. Then weigh it and soak it in
water for twenty-four hours. Weigh it again, and if it is more than
one fifth heavier than it was before soaking, it is not of the first
quality.
After the clay has been dug, it must be "tempered," that is, mixed
with water and about one third or one fourth as much sand as clay, and
left overnight in a "soak pit," a square pit about five feet deep. In
the morning the workmen shovel the mass over and feed it into the
machines for forming the bricks. The mixing is better done, however,
in a "ring pit." This is a circular pit twenty-five or thirty feet in
diameter, three feet deep, and lined with boards or brick. A big iron
wheel works from the center to the edge and back again for several
hours, through and through the clay. A method even better than this is
to put the clay and sand and water into a great trough, in which there
is a long shaft bristling with knives. The shaft revolves, mixes the
clay, and pushes it along to the end of the trough. This is called
"pugging," and the whole thing--trough, shaft, and knives--is a "pug
mill."
In the old days bricks were always made by hand. The moulder stood in
front of a wet table whereon lay a heap of soft clay. He either wet or
sanded his mould to keep it from sticking. Meanwhile, his assistant
had cut a piece of clay and rolled it and patted it into the shape of
the mould. In making bricks, there can be no patching; the mould
must be filled at one stroke, or else there will be folds in the
brick. To make a good brick, the moulder lifts the clay up above his
head and throws it into the mould with all his force. Then he presses
it into the corners with his thumbs, scrapes off with a strip of wood
any extra clay, or cuts it off with a wire, smooths the surface of the
brick, puts mould and brick upon a board, jerks the mould up and
proceeds to make another brick.
[Illustration: IN A NEW JERSEY BRICK MILL
_Copyright by Underwood and Underwood._
This man is moulding a fire-brick to its final shape.]
No matter how expert a moulder may be, brick-making by hand is slow
work, and in most places machines are used. In what is called the
"soft-mud" process, the clay is pushed on by the pug mill to the end
of the trough. There stands a mould for six bricks. A plunger forces
the clay into it, the mould is emptied, and in a single hour five
thousand bricks can be made. By what is called the "stiff-mud"
process, the stiff clay is put into a machine with an opening the size
of the end or side of a brick. The machine forces the clay through
this opening, cuts it off at the proper moment; and so makes bricks by
the thousand without either mould or moulder. A third way of making
brick is by what is called the "dry process." The clay is pulverized
and filled into moulds the length and breadth of a brick, but much
deeper, and with neither top nor bottom. One plunger from above and
another from below strike the clay in the mould with much force, and
make the fine, smooth brick known as "pressed brick." All this is done
by machinery, and some machines make six bricks at a time. These
"dry" bricks are fragile before they are burned, and must be handled
with great care.
Bricks cannot be put into the kiln while they are still wet, for when
a brick is drying, it is a delicate article. It objects to being too
hot or too cold, and it will not stand showers or drafts. In some way
about a pound of water must be dried out of each brick; but if you try
to hurry the drying, the brick turns sulky, refuses to have anything
more to do with you, and proceeds to crack. To dry, bricks are
sometimes spread on floors; or piled up in racks on short pieces of
board called "pallets"; and sometimes they are put upon little cars
and run slowly through heated tunnels. The last is the best way for
people who are in a hurry, for it takes only from twenty-four to
thirty-six hours to make the bricks ready to go to the kiln to be
burned.
In one sort of kiln, the bricks themselves make the kiln. They are
piled up in arches, but left a little way apart so the hot air can
move freely among them. The sides of the structure are covered with
burnt brick and mud, but the top is left open to allow the steam from
the hot bricks to escape. The fires are in flues that are left at the
bottom. They must burn slowly at first, but after a while, some forty
to sixty hours, the heat becomes intense. Thus far the bricks have
been grayish or cream-colored, but now, if there is iron in them, they
turn red; if there is lime, they turn yellow; if a large amount of
lime, they become flesh-colored. Besides this sort of kiln, which is
torn down when the bricks are sufficiently burned, there is also the
permanent kiln, which has fixed side walls and either an open or
closed top. Then, too, there is a "continuous" kiln. This has a number
of chambers, and the heat from each one passes into the next; so that
bricks in one chamber may be just warming up while in another they are
ready to be taken out.
When the bricks come out of the kiln, some of them are good and some
are not. Those that were on the outside are not burned enough; those
next it are not well baked, but can be used for the middle of thick
walls. The next ones are of good quality; but those directly over the
fires are so hard and brittle that they are of little use except for
pavements.
Paving-bricks, however, are not to be despised. They are not as smooth
and well finished as pressed brick, but they are exceedingly useful.
They need as much care in making as any others, and they must be
burned in a much hotter fire to make them dense and hard. The tests
for paving-bricks are quite different from those for ordinary
building-brick. If first-class paving-bricks weighing fifty pounds are
soaked in water for twenty hours, they take up so little water that
they will not weigh more than fifty-one or fifty-one and a half pounds
when taken out. To find out how hard they are, the bricks are weighed
and shaken about with foundry shot for a number of hours. Then they
are weighed again to see how much of their material has been rubbed
off. A third test is to put one brick on edge into a crushing machine
to see how much pressure it will stand. Paving-brick is cheaper than
granite blocks, and if it has a good foundation of concrete covered
with sand, it will last about three fourths as long. Brick is less
noisy than stone and is easier to clean.
Not so very long ago, when particularly handsome bricks were needed
for the outside of walls and other places where they would be
conspicuous, they were "re-pressed"; that is, they were made by hand
or in a "soft-mud" machine, and then, after drying for a while, were
put into a re-pressing machine to give them a smooth finish. These
machines are still used, but they are hardly necessary, for the
"dry-clay" brick machine will turn out a smooth brick in one
operation.
Another substance which is made of almost the same materials as brick
is terra cotta. To make this, fire brick, bits of pottery, partly
burned clay, and fine white sand are ground to a powder and mixed very
thoroughly. This mixture is moulded, dried, and burned. Until
recently, all terra cotta was of the color that is called by that
name, but now it is made in gray, white, and bronze as well.
Bricks are laid in mortar, and this makes a wall one solid mass and
stronger than it could be without any cement. But mortar does more
than this. It is more elastic than brick, and therefore, when a wall
settles, the mortar yields a little, and this often prevents the
bricks from cracking. Bricks are always thirsty, and if one is laid in
mortar, it will suck the moisture out of it almost as a sponge will
suck up water. The mortar thus has no chance to set, and so is not
strong as it should be. That is why the bricklayer wets his bricks,
especially in summer, before he puts them in place. Lime or cement
mortar will not set in freezing weather, and a brick building put up
in the winter is in danger of tumbling down when the warm days of
spring arrive.
This thirstiness of bricks is their greatest fault. Three or four days
of driving rain will sometimes wet through a brick wall two feet
thick, crumbling the plaster and spoiling the wallpaper. That is why
it is a poor plan to plaster directly on the brick wall of a house.
"Furring" strips, as they are called, or narrow strips of wood, should
be fastened on first and the laths nailed to these, or the wall can be
painted or oiled on the outside. The best way, however, though more
expensive, is to build the wall double. Then there is air between the
two thicknesses of brick. Air is a poor conductor of heat; so in
summer it keeps the heat out, and in winter it keeps it in.
But brick will suck up water from the ground as well as from a storm;
and therefore, when a brick house is to be built in a wet place, there
ought to be a three-eighths-inch layer of something waterproof, like
asphalt and coal tar, put on top of one of the layers of brickwork to
prevent the moisture from creeping up.
Bricks have their faults, but they will not burn, and when properly
used, they make a most comfortable and enduring house.
V
AT THE GOLD DIGGINGS
When gold was first discovered in California, in 1848, people from all
over the world made a frantic rush to get there, every one of them
hoping that he would be lucky enough to make his fortune, and fearing
lest the precious metal should be gone before he could even begin to
dig. The gold that these men gathered came from what were called
"placers"; that is, masses of gravel and sand along the beds of
mountain streams. Each miner had a pan of tin or iron, which he filled
half-full of the gravel, or "pay dirt," as the miners called it. Then,
holding it under water, he shook off the stones and mud over the side
of the pan, leaving grains of gold mixed with black sand at the
bottom. This black sand was iron, and after a while the miners removed
it with a magnet, dried what remained, and blew away the dust, leaving
only the grains of gold.
Another contrivance which soon came into use was the "cradle." This
was a long box, sometimes only a hollowed-out log. At the top was a
sieve which sifted out the stones. Nailed to the bottom of the cradle
were small cleats of wood, or "riffles," which kept the water from
running so fast as to sweep the gold out of the cradle with it. The
cradle was placed on rockers and was also tilted slightly. The miner
shoveled the gravel into the top of the cradle and his partner rocked
it. The sieve kept back the stones, the water broke up the lumps of
earth and gravel and washed them down the cradle, and the grains of
gold were stopped by the riffles, and sank to the bottom. Sometimes
the "pay dirt" continued under a stream. To get at it, the miners
often built a little canal and turned the water into a new channel;
then they could work on the former bed of the river.
Before many years had passed, the gold that was near the surface had
been gathered. The miners then followed the streams up into the
mountains, and found that much of the gold had come from beds where in
ancient times rivers had flowed. There was gold still remaining in
these beds, but it was poorly distributed, the miners thought.
Sometimes there would be quite an amount in one place, and then the
miner would dig for days without finding any more. Even worse than
this was the fact that these gravel beds were not on the top of the
ground, but were covered up with soil and trees. Evidently the slow
work with pans and cradles would not pay here; but it occurred to some
one that if a powerful stream of water could be directed against the
great banks of earth, as water is directed against a burning building,
they would crumble, the dirt could be washed down sluices, and the
gold be saved. This was done. Great reservoirs were built high up in
the mountains, and water was brought by means of ditches or pipes to a
convenient place. Then it was allowed to rush furiously through a
hose and nozzle, and the great stream coming with tremendous force was
played upon the banks of gravel. The banks crumbled, the gravel was
washed into a string of sluices, or long boxes with riffles to catch
the gold. Soon the miners found that if quicksilver was put into these
sluices, it would unite with the gold and make a sort of paste called
"amalgam." Then if this amalgam was heated, the quicksilver would be
driven off in the form of gas, and the gold would remain in a
beautiful yellow mass.
[Illustration: HYDRAULIC GOLD MINING
A placer mine at Gold Point, California, where tremendous streams of
water under high pressure are busy washing away the side of a
gold-bearing hill.]
The ancient rivers had also carried gold to the valleys, and to
collect this a dredge, which the miners called a "gold ship," came
into use. The "ship" part of this machine is an immense flat scow.
Stretching out from one end is something which looks like a moving
ladder. This is the support of an endless chain of buckets, each of
which can bite into the gravel and take a mouthful of five or six
hundred pounds. They drop this gravel into a big drum which is
continually revolving. Water flows through the drum, and washes out
the sand and bits of gold over large tables, where by means of riffles
and quicksilver the gold is captured. This scow was usually on dry
land at first; but its digging soon made a lake, and then it floated.
It must be more fascinating to hold a pan in your own hands and pick
out little grains of gold or perhaps even a big piece of it with your
own fingers, but if the gravel is good the dredge makes more money.
In Alaska the great difficulty in mining is that, except at the
surface, the ground is frozen all the year round. At first, the miners
used to thaw the place where they wished to dig by building wood
fires; but this was a slow method, and now the thawing is done by
steam. They carry the steam in a pipe to the place where the digging
is to be done, and send it through a hose. At the end of the hose is a
pointed steel tube. They hammer this tube into the ground and let some
steam pass through the nozzle. This softens the ground so that picks
and shovels may be used. There is generally cold enough in Alaska, but
once at least the miners had to manufacture it. The gold-bearing
gravel was deep, the ground was flat, and it was often overflowed.
They set up a freezing plant, and shut in their land with a bulkhead
of ice several feet thick. Then they pumped out what water was already
in and did their work with no more trouble.
When gold began to grow less in the California gravel, the miners
looked for it in the rocks on the mountain-side. The placer miners
laughed at them and called their shafts "coyote holes"; but in time
the placers failed, while nearly all of our gold to-day comes from
veins of white quartz in the rocks. A vein of gold is the most
capricious thing in the world. It may be so tiny that it can hardly be
seen, then widen and grow rich in gold, then suddenly come to an end.
This is why a new mine is so uncertain an enterprise. The gold may
hold out and bring fortunes to the investors, or it may fail, and then
all they will have to show for their money is the memory that they
put it into a hole in the ground. The managers of a few of the
well-established mines, however, have explored so far as to make sure
that there is gold enough for many years of digging.
The mining engineer must be a very wide-awake man. It is not enough
for him simply to remember what was taught him in the schools of
mining; he must be bright enough to invent new ways of meeting
difficulties. No two mines are alike, and he must be ready for all
sorts of emergencies. A gold mine now consists of a shaft or pit dug
several hundred feet down into the rock, with levels or galleries
running off from it and with big openings like rooms made where the
rock was dug out. The roofs of the rooms are supported by great
timbers. To break away the rock, the miner makes a hole with a rock
drill worked by electricity or compressed air, puts powder or dynamite
into the hole and explodes it. The broken rock is then raised to the
surface and crushed in a "stamping mill." Here the ore is fed into a
great steel box called a "mortar." Five immense hammers, often
weighing a thousand pounds apiece, drop down upon the ore, one after
another, until it is fine enough to go through a wire screen in the
front of the box. When two hundred or more of these hammers are
pounding away with all their might, a stamping mill is a pretty noisy
place. The ore, crushed to a fine mud, now runs over sloping tables
covered with copper. Sticking to the top of the copper is a film of
quicksilver. This holds fast whatever gold there may be and makes an
amalgam, which is scraped off from time to time, and the quicksilver
is driven from the gold by heat.
Gold that is not united with other metals is called "free milling
gold." Much of it, however, is found in combination with one metal or
another, and is known as "rebellious" or "refractory" gold. Such gold
may sometimes be set free by heat, and sometimes by chemicals. One way
is by the use of chlorine gas, and the story of it sounds almost like
"The house that Jack built." It might run somewhat like this: This is
the salt that furnishes the chlorine. This is the chlorine gas that
unites with the gold. This is the chloride that is formed when the
chlorine gas unites with the gold. This is the water that washes from
the tank the chloride that is formed when the chlorine gas unites with
the gold. This is the sulphate of iron that unites with the chlorine
gas of the chloride that the water washes from the tank that is formed
when the chlorine gas unites with the gold--and leaves the gold free.
Another method is by the use of cyanide. More than a century ago a
chemist discovered that if gold was put into water containing a little
cyanide, the gold would dissolve, while quartz and any metals that
might be united with the gold would settle in the tank. The water in
which the gold is dissolved is now run into boxes full of shavings of
zinc and is "precipitated" upon them; that is, the tiny particles of
gold in the water fall upon the zinc and cling to it. Zinc melts more
easily than gold, so if this gilded zinc is put into a furnace, the
zinc melts and the gold is set free.
Very often gold is found combined with lead or copper. It must then be
melted or smelted in great furnaces. The metal is heavier than the
rock and settles to the bottom of the furnace. It is then drawn off
and the gold is separated from the other metals, usually by
electricity.
Sometimes large pieces of gold called "nuggets" are found by miners.
The largest one known was found in Australia. It weighed 190 pounds
and was worth $42,000. Sometimes spongy lumps of gold are found; but
as a general thing gold comes from the little specks scattered through
veins in rock, and much work has to be done before it can be made into
coins or jewelry. It is too soft for such uses unless some alloy,
usually copper or silver, is mixed with it to make it harder.
Sometimes it is desirable to know how much alloy has been added. The
jeweler then makes a line with the article on a peculiar kind of black
stone called a "touchstone," and by the color of the golden mark he
can tell fairly well how nearly pure the article is. To be more
accurate, he pours nitric acid upon the mark. This eats away the alloy
and leaves only the gold.
Gold is a wonderful metal. It is of beautiful color; it can be
hammered so thin that the light will shine through it; few acids
affect it, and the oxygen which eats away iron does not harm it. Pure
gold is spoken of as being "twenty-four carats fine," from _carat_, an
old weight equal to one twenty-fourth of an ounce troy. Watchcases
are from eight to eighteen carats fine; chains are seldom more than
fourteen; and the gold coins of the United States are about eleven
parts of gold and one of copper. Coins wear in passing from one person
to another, and that is why the edges are milled, so that it may be
more easily seen when they have become too light to be used as coins.
When such pieces come into the hands of the Government, they must be
recoined.
VI
THE STORY OF A SILVER MINE
A man who goes out in search of a mine is called a "prospector." The
best prospector is a man who has learned to keep his eyes open and to
recognize the signs of gold and silver and other metals. A faithful
friend goes with him, a donkey or mule which carries his bacon and
beans, blankets, saucepan, and a few tools, such as a pan, pick,
shovel, hammer, and axe. Sometimes the prospector also takes with him
a magnifying glass and a little acid to test specimens, but usually he
trusts to his eyes alone.
When these few things have been brought together, the prospector and
the donkey set out. They wander over the hills and down into the
canyons. If a rock is stained red, the prospector examines it to see
whether it contains iron; if it is green, he looks for copper. In the
canyons and along the creeks he often tests the gravel for traces of
some valuable metal. If he finds any of these traces along the stream,
he follows them on the bank until they stop; then he carefully
examines the bank of the stream or the nearest hillside. If he
continues to find bits of metal, they will lead him to a vein of ore,
from which they have been broken by the wind, rain, and frost.
Generally a prospector is looking for some one special metal, and in
his search he often overlooks some other metal; for instance,
thousands of the gold-seekers who rushed to California in 1849 hurried
through Nevada on their way. If they had only known what was under
their feet, they would have taken their picks and shovels and begun to
dig, instead of trying to get out of the region as soon as might be.
Ten years later, the California placers were becoming exhausted, and
miners began to go elsewhere in their search for gold.
Among those who were working in what is now the State of Nevada were
two Irishmen who had been unlucky in California and had fared no
better in Nevada. They wanted to go somewhere else, but they had not
money enough for the journey; so they kept on with their work at the
foot of Mount Davidson, washing the gravel and saving the little gold
that they found. They were annoyed by some heavy black stuff that
united with the quicksilver in their cradles, interfered with the
saving of the gold, and put them in a very bad temper. At length a man
named Henry Comstock came along, who told them that this black stuff
was silver ore. They examined the mountain-side, and discovered the
outcrop or edge of a great vein containing gold and also silver. It is
no wonder that people rushed from the east and west to the wonderful
new mines, for it was plain that these new "diggings" were not mere
placers, but rich veins that many years of working might not exhaust.
Every newcomer hoped to discover a vein; and within a year or two the
district around the Comstock lode was full of deep shafts, many of
them abandoned and half-hidden by low brush, but some of them yielding
quantities of gold and silver. Before this, there had been only about
a thousand people in what is now Nevada, but in two years after the
discovery of silver, there were 16,000, and a new Territory was
formed.
The miners knew how to get gold out of ore, but silver was another
matter, and some of it was difficult to extract. They had so much
trouble that they were ready to believe in any treatment of the ore,
no matter how absurd, that promised to help them out of their
difficulties. Some of them were actually persuaded that the juice of
the wild sagebrush would bring the silver out. It is no wonder that
they were troubled, for in the Comstock lode were not only gold and
silver, but ten or twelve other metals or combinations of silver with
something else. At length processes were invented for treating the
different kinds of ore. Some kinds were crushed in a stamping mill,
then ground to a powder and mixed with quicksilver or mercury. This
mercury united with both the gold and the silver, making an amalgam.
The amalgam, together with the finely ground ore, was put into a
"settler," and here the heavy amalgam sank to the bottom and was then
strained. The extra mercury was collected, and the amalgam was put
into a retort or kettle and heated. The mercury became a gas and was
driven off from the gold and silver, then caught in a vessel cool
enough to condense it, just as a cold plate held in steam will
collect drops of water. Sometimes the ore was mixed with copper and
lead. In that case common salt and copper sulphate were used. Some ore
had to be roasted in a furnace in order to drive off the sulphur.
[Illustration: THE STORY OF A SPOON
_Courtesy The Gorham Co._
(1) Silver strip blanked. (2) Pinched. (3) Graded. (4) Outlining of
Handle. (5) Stamped Handle. (6) Spoon completely trimmed. (7, 8)
Finished spoons.]
There were great and unusual dangers to be met in getting the ore. The
vein of quartz which bore it was fifty or sixty feet wide. Some was
hard, and some so soft and crumbling that pillars would not hold up
the roof. The passageways were then lined with heavy logs standing on
either side, other logs laid across their tops, and all bolted firmly
together. Nevertheless, they twisted and fell, and slowly but
certainly the whole mass of earth and rock, two hundred or more feet
in thickness, was coming down upon the heads of the miners. The work
on the Comstock mines had come to an end unless a man could be found
able to invent some system of support not laid down in the books. The
man was found. He took short, square timbers five or six feet long,
put them together as if they were the sides and ends of square boxes,
and piled them one above another, making hollow pillars. He fastened
these firmly together and filled the space inside with waste rock,
thus making strong, solid pillars that would support almost any weight
that could be put upon them.
There were two other dangers, water and heat. The vein was porous and
water was constantly trickling out of it. Then, too, there were "water
pockets," or natural reservoirs in the rock, and any moment the
stroke of a pick might let out a torrent and force the miners to run
for their lives. Sometimes minerals were dissolved in this water, and
the men with closed eyes and swollen faces had to be hurried to the
surface for treatment. Powerful pumps had to be used and the water
sent away through long lines of pipes. This water was warm, and in
very deep workings in the Comstock vein it was boiling hot. Even with
quantities of ice sent down to cool them, the men could work in some
places only a short time.
In San Francisco there was a mining engineer named Adolph Sutro who
planned to remedy these troubles by driving a big four-mile tunnel
through the heart of the mountain, letting out the hot water and the
foul air. The owners of some of the mines joined him in raising the
money, and the tunnel was dug. Through this the water ran out. The
mines were freed of foul air and fresh air was driven in.
The Comstock lode has given up an amazing amount of precious metal.
Between 1860 and 1890 it produced $340,000,000. After 1890, however,
its product grew less. The vein was not so rich, the price of silver
fell, while the cost of mining it at great depths increased. Not
nearly so much was mined, and at length water rose in the mines up to
the level of the Sutro Tunnel. In 1900 new machinery was put in and
new methods were adopted, such as treating the tailings with cyanide
and so saving much of the precious metal from them. From the beginning
the Comstock mines have been so ready to follow improved methods that
they have been called the mining school of the world.
Great quantities of silver are used for making jewelry and for
tableware. The one objection to its use is that silver likes to unite
with sulphur, and thus the silver easily becomes black. There is
sulphur in the yolk of an egg and that is why the spoon with which it
has been eaten turns black. Even if silverware is not used, it
tarnishes, especially in towns, because there is so much sulphureted
hydrogen in the air. In perfectly pure air, it would not tarnish.
Silver is harder than gold, but not hard enough to be used without
some alloy, usually copper. Tableware is "solid" even if it contains
alloy enough to stiffen it. It is "plated" if it is made of some
cheaper metal and covered with silver. The old way of doing this was
to fasten with bits of solder a thin sheet of silver to the cup or
vase or whatever was in hand and heat it. This did fairly well for
large, smooth articles; but it was almost impossible to finish the
edges of spoons so as not to show the two metals. If you look at a
plated spoon to-day, however, you will find that there is no break at
the edge, and so far as you can tell by the eye, it is solid silver.
If you look on the back of the spoon, you will perhaps see "Rogers
Bros. 1846." These men were the first silvermakers in this country to
plate tableware by electricity. To make a spoon, they formed one out
of iron or copper and made sure that it was perfectly clean. Then
across a bath of silver cyanide, potassium cyanide, and water they
laid two metal rods, and from these they hung a spoon at one end and a
plate of silver at the other. These rods were connected with the two
poles of a battery. The electrical current passed through them,
released the silver from the silver cyanide, and this was deposited
upon the spoon. The cyanide that had lost its silver took enough more
from the silver plate to make up. The amount of silver on the spoon
depends upon the length of time it remains in the bath. It is weighed
before plating and again afterwards, to make sure that the proper
amount of silver has been deposited upon it. On the back of many
plated articles you will see the words "Triple plate" or "Quadruple
plate." If the article has been made by a reliable firm, this means
that the triple plate it manufactures contains three times as much
silver as "single plate," and that quadruple plate contains four times
as much. A piece of silver looks just as well if it has stayed in the
bath only a few minutes, but of course it has taken on so little
silver that this will soon wear off and show the cheaper metal.
A large amount of silver is used for coins. When the United States
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° 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.
People often say that the latter half of the nineteenth century was
the Age of Steel, because so many new uses for steel were found at
that time. The twentieth century promises to be the Age of
Electricity, and electricity must have copper. Formerly iron was used
for telegraph wires; but it needs much more electricity to carry power
or light or heat or a telegraphic message over an iron wire than one
of copper. Moreover, iron will rust and will not stretch in storms
like copper, and so needs renewing much oftener. Electric lighting and
the telephone are everywhere, even on the summits of mountains and in
mines a mile below the earth's surface. Electric power, if a
waterfall furnishes the electricity, is the cheapest power known. The
common blue vitriol is one form of copper, and to this we owe many of
our electric conveniences. It is used in all wet batteries, and so it
rings our doorbells for us. It also sprays our apple and peach trees,
and is a very valuable article. Indeed, copper in all its forms, pure
and alloyed, is one of our best and most helpful friends.
IX
THE NEW METAL, ALUMINUM
Not many years ago a college boy read about an interesting metal
called "aluminum." It was as strong as iron, but weighed only one
third as much, and moisture would not make it rust. It was made of a
substance called "alumina," and a French chemist had declared that the
clay banks were full of it; and yet it cost as much as silver. It had
been used in France for jewelry and knicknacks, and a rattle of it had
been presented to the baby son of the Emperor of France as a great
rarity.
The college boy thought by day and dreamed by night of the metal that
was everywhere, but that might as well be nowhere, so far as getting
at it was concerned. At the age of twenty-one, the young man
graduated, but even his new diploma could not keep his mind away from
aluminum. He borrowed the college laboratory and set to work. For
seven or eight months he tried mixing the metal with various
substances to see if it would not dissolve. At length he tried a stone
from Greenland called "cryolite," which had already been used for
making a kind of porcelain. The name of this stone comes from two
Greek words meaning "ice stone," and it is so called because it melts
so easily. The young student melted it and found that it would
dissolve alumina. Then he ran an electric current through the melted
mass, and there was a deposit of aluminum. This young man, just out of
college, had discovered a process that resulted in reducing the cost
of aluminum from twelve dollars a pound to eighteen cents. Meanwhile a
Frenchman of the same age had been working away by himself, and made
the same discovery only two months later.
Aluminum is now made from a mineral called "bauxite," found chiefly in
Georgia, Alabama, and Arkansas. Mining it is much more agreeable than
coal mining, for the work is done aboveground. The bauxite is in beds
or strata which often cover the hills like a blanket. First of all,
the mine is "stripped,"--that is, the soil which covers the ore is
removed,--and then the mining is done in great steps eight or ten feet
high, if a hill is to be worked. There is some variety in mining
bauxite, for it occurs in three forms. First, it may be a rock, which
has to be blasted in order to loosen it. Second, it may be in the form
of gray or red clay. Third, it occurs in round masses, sometimes no
larger than peas, and sometimes an inch in diameter. In this form it
can easily be loosened with a pickaxe, and shoveled into cars to be
carried to the mill. Bauxite is a rather mischievous mineral and
sometimes acts as if it delighted in playing tricks upon managers of
mines. The ore may not change in the least in its appearance, and yet
it may suddenly have become much richer or much poorer. Therefore the
superintendent has to give his ore a chemical test every little while
to make sure that all things are going on well.
This bauxite is purified, and the result is a fine white powder, which
is pure alumina, and consists of the metal aluminum and the gas
oxygen. Cryolite is now melted by electricity. The white powder is put
into it, and dissolves just as sugar dissolves in water. The
electricity keeps on working, and now it separates the alumina into
its two parts. The aluminum is a little heavier than the melted
cryolite, and therefore it settles and may be drawn off at the bottom
of the melting-pot.
There are a good many reasons why aluminum is useful. As has been said
it is strong and light and does not rust in moisture. You can beat it
into sheets as thin as gold leaf, and you can draw it into the finest
wire. It is softer than silver, and it can be punched into almost any
form. It is the most accommodating of metals. You can hammer it in the
cold until it becomes as hard as soft iron. Then, if you need to have
it soft again, it will become so by melting. It takes a fine polish
and is not affected, as silver is, by the fumes which are thrown off
by burning coal; and so keeps its color when silver would turn black.
Salt water does not hurt it in the least, and few of the acids affect
it. Another good quality is that it conducts electricity excellently.
It is true that copper will do the same work with a smaller wire; but
the aluminum is much lighter and so cheap that the larger wire of
aluminum costs less than the smaller one of copper, and its use for
this purpose is on the increase. It conducts heat as well as silver.
If you put one spoon of aluminum, one of silver, and one that is
"plated" into a cup of hot water, the handles of the first two will
almost burn your fingers before the third is at all uncomfortable to
touch.
[Illustration: A "MOVIE" OF AN ALUMINUM FUNNEL
_Courtesy The Aluminum Cooking Utensil Company._
Seventeen other operations are necessary after the thirteenth stamping
operation before the funnel is ready to be sold. And after all this
work, we can buy it for 35 cents at any hardware store.]
Aluminum is found not only in clay and indeed in most rocks except
sandstone and limestone, but also in several of the precious stones,
in the yellow topaz, the blue sapphire and lapis-lazuli, and the red
garnet and ruby. It might look down upon some of its metallic
relatives, but it is friendly with them all, and perfectly willing to
form alloys with most of them. A single ounce of it put into a ton of
steel as the latter is being poured out will drive away the gases
which often make little holes in castings. Mixed with copper it makes
a beautiful bronze which has the yellow gleam of gold, but is hard to
work. When a piece of jewelry looks like gold, but is sold at too low
a price to be "real," it may be aluminum bronze, very pretty at first,
but before long its luster will vanish. Aluminum bronze is not good
for jewelry, but it is good for many uses, especially for bearings in
machinery. Aluminum mixed with even a very little silver has the color
and brightness of silver. The most common alloys with aluminum are
zinc, copper, and manganese, but in such small quantities that they do
not change its appearance.
With so many good qualities and so few bad ones, it is small wonder
that aluminum is employed for more purposes than can be counted. A
very few years ago it was only an interesting curiosity, but now it is
one of the hardest-worked metals. Automobiles in particular owe a
great deal to its help. When they first began to be common, in
1904-05, the engines were less powerful than they are now made, and
aluminum was largely employed in order to lessen the weight. Before
long it was in use for carburetors, bodies, gear-boxes, fenders,
hoods, and many other parts of the machine. Makers of electric
apparatus use aluminum instead of brass. The frames of opera glasses
and of cameras are made of it. Travelers and soldiers and campers,
people to whom every extra ounce of weight counts, are glad enough to
have dishes of aluminum. The accommodating metal is even used for
"wallpaper," and threads of it are combined with silk to give a
specially brilliant effect on the stage. It can be made into a paint
which will protect iron from rust; and will make woodwork partially
fireproof.
Aluminum has been gladly employed by the manufacturers of all sorts of
articles, but nowhere has its welcome been more cordial than in the
kitchen. Any one who has ever lifted the heavy iron kettles which were
in use not so very many years ago will realize what an improvement it
is to have kettles made of aluminum. But aluminum has other advantages
besides its lightness. If any food containing a weak acid, like
vinegar and water, is put into a copper kettle, some of the copper
dissolves and goes into the food; acid does not affect aluminum except
to brighten it if it has been discolored by an alkali like soda. "Tin"
dishes, so called, are only iron with a coating of tin. The tin soon
wears off, and the iron rusts; aluminum does not rust in moisture. A
strong alkali will destroy it, but no alkali in common use in the
kitchen is strong enough to do more harm than to change the color, and
a weak acid will restore that. Enameled ware, especially if it is
white, looks dainty and attractive; but the enamel is likely to chip
off, and, too, if the dish "boils dry," the food in it and the dish
itself are spoiled. Aluminum never chips, and it holds the heat in
such a manner as to make all parts of the dish equally hot. Food,
then, is not so likely to "burn down," but if it does, only the part
that sticks will taste scorched; and no matter how many times a dish
"boils dry," it will never break. If you make a dent in it, you can
easily pound it back into shape again. It is said that an aluminum
teakettle one sixteenth of an inch in diameter can be bent almost
double before it will break.
Aluminum dishes are made in two ways. Sometimes they are cast, and
sometimes they are drawn on a machine. If one is to be smaller at the
top, as in the case of a coffeepot, it is drawn out into a cylinder,
then put on a revolving spindle. As it whirls around, a tool is held
against it wherever it is to be made smaller, and very soon the
coffeepot is in shape. The spout is soldered on, but even the solder
is made chiefly of aluminum.
Aluminum dishes may become battered and bruised, but they need never
be thrown away. There is an old story of some enchanted slippers which
brought misfortune to whoever owned them. The man who possessed them
tried his best to get rid of the troublesome articles, but they always
returned. So it is with an aluminum dish. Bend it, burn it, put acid
into it, do what you will to get rid of it, but like the slippers it
remains with you. Unlike them, however, it brings good fortune,
because it saves time and trouble and patience and money.
A few years ago the motive power for most manufactures was steam.
Electricity is rapidly taking its place; and if aluminum was good for
nothing else save to act as a conductor of electricity in its various
applications, there would even then be a great future before it.
X
THE OIL IN OUR LAMPS
Probably the first man who went to a spring for a drink and found oil
floating on the water was decidedly annoyed. He did not care in the
least where the oil came from or what it was good for; he was thirsty,
and it had spoiled his drink, and that was enough for him. We know now
that oil comes chiefly from strata of coarse sandstone, but we are not
quite sure how it happened to be there. The sand which formed these
strata was deposited by water ages and ages ago--we are certain of
that. Another thing that we are certain of is that where the strata
lie flat, there is no oil. Hot substances become smaller as they cool;
and as the earth grew cooler, it became smaller. The crust of the
earth wrinkled as the skin of an apple does when it dries. In the tops
of these great sandstone wrinkles there is often gas; and below the
gas is the place where oil is found. There is no use in looking for
petroleum where the folds of the strata are very sharp, because in
that case the strata crack and let the oil flow away. It is not in
pools, but the porous stone holds it just as a sponge holds water. If
you drop a little oil upon a stone even much less porous than
sandstone, it will not be easy to wipe it off, because some of it will
have sunk into the stone.
In many places the gas forces its way out, and is piped to carry to
houses for light and heat. Not far above Niagara Falls there was a
spring of gas which flowed for years. An iron pipe was put down, and
when the gas was lighted, the flame shot up three or four feet. The
gas came with such force that a handkerchief put over the end of the
pipe would not burn, though the flame would blaze away above it. In
the country of the fire worshipers, on the shores of the Caspian Sea,
fires of natural gas have been burning for ages, kindled, perhaps, by
lightning centuries ago. There is a vast supply of oil in this place;
and indeed there is hardly a country that has not more or less of it.
In the United States the colonists soon learned that there was
petroleum in what is now the State of New York; but New York was a
long way from the Atlantic seaboard in those days, and they went on
contentedly burning candles or sperm whale oil, or, a little later, a
rather dangerous liquid which was known as "fluid." The Indians
believed that the oil which appeared in the springs was a good
medicine. They threw their blankets upon the water, and when these had
become saturated with the oil, they wrung them out and sold the oil.
Those were the times when if a medicine only tasted and smelled bad
enough, people never doubted that it would cure all their diseases,
and they gladly bought the oil of the Indians.
When at last it became clear to the members of an enterprising company
that oil for use in lamps could be made from petroleum, they secured
some land in Pennsylvania that seemed promising and set to work to
dig a well. But the more they dug, the more the loose dirt fell in
upon them. Fortunately for the company, the superintendent had brains,
and he thought out a way to get the better of the crumbling soil. He
simply drove down an iron pipe to the sandstone which contained the
oil, and set his borer at work within the pipe. One morning he found
that the oil had gushed in nearly to the top of the well. He had
"struck oil."
This was about ten years after the rush to California for gold, and
now that this cheaper and quicker method of making a well had been
invented, there was almost as much of a rush to Pennsylvania for oil.
With every penny that they could beg or borrow, people from the East
hurried to the westward to buy or lease a piece of land in the hope of
making their fortunes. A song of the day had for its refrain,--
"Stocks par, stocks up,
Then on the wane;
Everybody's troubled with
Oil on the brain."
In the course of a year or two, the first "gusher" was discovered. The
workmen had drilled down some four or five hundred feet and were
working away peacefully, when a furious stream of oil burst forth
which hurled the tools high up into the air. Hundreds of barrels
gushed out every day, and soon other gushers were discovered. The most
famous one in the world is at Lakeview, California. For months it
produced fifty thousand barrels of oil a day, and threw it up three
hundred and fifty feet into the air in a black column, spraying the
country with oil for a mile around. The oil flowed away in a river,
and for a time no one could plan any way to stop it or store it. At
last, however, a mammoth tank was built around the well and made firm
with stones and bags of earth. This was soon full of oil; and with all
this vast weight of oil pressing down upon it, the stream could not
rise more than a few feet above the surface. Just why oil should come
out with such force, the geologists are not quite certain; but it is
thought to result from a pressure of gas upon the sandstone containing
it. The flow almost always becomes less and less, and after a time the
most generous well has to be pumped.
[Illustration: A CALIFORNIA OIL FIELD
For scenery, one should not go to an oil field. Looks, smell, and oil
alike are unpleasant, but every oil derrick covers a fortune and helps
to make our machinery run smoothly.]
An "oil field" may extend over thousands of square miles; but within
this field there are always "pools"; that is, certain smaller fields,
where oil is found. When a man thinks there is oil in a certain spot,
sometimes he buys the land if he is able; but oftener he gets
permission of the owner to bore a well, agreeing to pay him a royalty;
that is, a certain percentage of all the oil that is produced. When
this has been arranged, he builds his derrick. This consists of four
strong upright beams firmly held together by crossbeams. It stands
directly over the place where the well is to be dug. It is from thirty
to eighty feet in height, according to the depth at which it is hoped
to find oil. There must also be an engine house to provide the power
for drilling. An iron pipe eight or ten inches in diameter is driven
down through the soil until it comes to rock. Now the regular drilling
begins. At the top of the derrick is a pulley. Over the pulley passes
a stout rope to which the heavy drilling tools--the "string of tools,"
as they are called--are fastened. The drilling goes on day and night.
The drill makes the hole, and the sand pump sucks out the water and
loose bits of stone. When the drill has gone to the bottom of the
strata which carry water, the sides of the bore are cased to keep the
water out; then the drilling continues, but now the drill makes its
way into the oil-bearing sandstone.
There is nothing certain about the search for oil. In some places it
is near the surface, in others it is perhaps three or four thousand
feet down. The well may prove to be a gusher and pour out hundreds of
thousands of gallons a day; or the oil may refuse to rise to the
surface and have to be pumped out even at the first. Naturally, no one
is prepared for a gusher, and millions of gallons have often flowed
away before any arrangements could be made for storing the oil.
Sometimes a well that gives only a moderate flow can be made to yield
generously by exploding a heavy charge of dynamite at the bottom, to
break up the rock and, it is always hoped, to open some new
oil-holding crevice that the drill has not reached.
Crude petroleum is a dark, disagreeable, bad-smelling liquid; and
before it can be of much use, it must be refined. For several years it
was carried in barrels from the oil fields to Pittsburgh by wagon and
boat, a slow, expensive process, and generally unsatisfactory to all
but the teamsters. Then came the railroads. They provided iron tanks
in the shape of a cylinder fastened to freight cars, much like those
employed to-day. There was only one difficulty about sending oil by
rail, and that was that it still had to be hauled by team to the
railroad, sometimes a number of miles. At length, some one said to
himself, "Why cannot we simply run a pipe directly from the well to
the railroad?" This was done. Pumping engines were put in a few miles
apart, and the invention was a success in the eyes of all but the
teamsters. In spite of their opposition, however, pipe-lines
increased.
Before this it had been necessary to build the refineries as near the
oil regions as possible in order to save the expense of carrying the
oil; but now they could be built wherever it was most convenient.
To-day oil can be brought at a small expense from west of the
Mississippi River to the Atlantic seaboard, refined, and distributed
throughout that part of the country, or loaded into "tankers,"--that
is, steamships containing strong tanks of steel,--and so taken across
the ocean. The pipes are made of iron and are six or eight inches or
more in diameter. In using them one difficulty was found which has
been overcome in an ingenious fashion. Sometimes they become choked by
the impurities of the oil and the flow is lessened. Then a "go-devil"
is put into them. This is shaped like a cartridge, is about three
feet in length, composed of springs and plates of iron and so flexible
that it can turn around a corner. It is so made that as it slips down
the current of oil, it whirls around and in so doing its nose of sharp
blades scrapes the pipes clean.
The pipes go over hills and through swamps. They cross rivers
sometimes by means of bridges, and sometimes they are anchored to the
bed of the stream. If they have to go through a salt marsh, they are
laid in concrete to preserve the iron. If these lines were suddenly
destroyed and oil had to be carried in the old way, kerosene would
become an expensive luxury.
Getting the oil out of the ground and carried to the refineries is not
all of the business by any means. The early oils crusted on the lamp
wicks, their smell was unendurable, and they were given to exploding.
Evidently, if oil was to be used for lighting, it must be improved,
and the first step was to distil it. To distil anything means to boil
it and collect the vapor. If you hold a piece of cold earthenware in
the steam of a teakettle, water will collect on it. This is distilled
water, and is purer than that in the kettle. Petroleum was at first
distilled in a rough way; but now it is done with the utmost care and
exactness. The crude oil is pumped into boilers holding six hundred
barrels or more. The fires are started, and the oil soon begins to
turn into vapor. This vapor passes through coils of pipe or long,
straight, parallel pipes. Cold water is pumped over these pipes, the
vapor turns into a liquid again, and we have kerosene oil.
This is the outline of the process, but it is a small part of the
actual work in all its details. Kerosene oil is only one of the many
substances found in petroleum. Fortunately, some of these substances
are light, like gasoline and benzine; some, like kerosene, are
heavier; and paraffin and tar are heaviest of all. There are also
gases, which pass off first and are saved to help keep the furnace
going. Then come the others, one by one, according to their weight.
The stillman keeps close watch, and when the color and appearance of
the distillate changes, he turns it off into another tank. This
process is called "fractional distillation," and the various products
are called "fractions." No two kinds of petroleum and no two oil wells
are just alike, and it needs a skillful man to manage either.
Even after all this distillation, the kerosene still chars the wick
somewhat--which prevents the wick from drawing up the oil
properly--and it still has a disagreeable smell. To fit it for burning
in lamps, it must be treated with sulphuric acid, which carries away
some of the impurities, and then with caustic soda, which carries away
others. Before it can be put on the market, it is examined to see
whether it is of the proper color. Then come three important tests.
The first is to see that it is of the proper weight. If it is too
heavy, it will not burn freely enough; if it is too light, then there
is too much of the lighter oils in it for safety. The second test is
the "flash test." The object of this is to see how hot the oil must be
before it gives off a vapor which will burn. The third, the "burning
test," is to discover how hot the oil must be before it will take fire
and burn on the surface. Most civilized countries make definite laws
forbidding the sale of kerosene oil that is not up to a standard of
safety. Oil for use in lamps should have an open flash test of at
least 100° F. and a burning point of not less than 125° F.
We say that we burn oil in our lamps, but what we really do is to heat
the oil until it gives off gas, and then we burn the gas. To keep the
flame regular and help on the burning, we use a chimney on the lamp.
The hot air rises in the chimney and the cold air underneath rushes in
to take its place and brings oxygen to the flame. In a close, stuffy
room no lamp will give a good clear light, because there is not oxygen
enough for its flame. Let in fresh air, and the light will be
brighter. If you hold a cold plate in the flame before the chimney is
put on, soot or carbon will be deposited. A lamp gives light because
these particles of carbon become so hot that they glow. In lamps using
a "mantle," there is the glow not only of these particles, but also of
the mantle. In a wax candle, we light the wick, its heat melts the wax
and carries it to the flame. When the wax is made hot enough, it
becomes gas, and we burn the gas, not the wax. Wax alone will melt,
but not take fire even if a burning match is held to it. The reason is
that the match does not give heat enough to turn the wax into gas. But
put a bit of wax upon a bed of burning coals, where there is a good
supply of heat, and it will turn into gas and burn.
The products made from petroleum are as different in their character
and uses as paraffin and naphtha. Some of them are used for oiling
machinery; tar is used for dyes; naphtha dissolves resin to use in
varnish; benzine is the great cleanser of clothes, printers' types,
and almost everything else; gasoline runs automobiles, motors, and
many sorts of engines; paraffin makes candles, seals jelly glasses,
covers the heads of matches so that they are no longer spoiled by
being wet, and makes the ever-useful "waxed paper"; printers' ink and
waterproof roofing-paper both owe a debt to petroleum. Even in
medicine, though a little petroleum is no longer looked upon as a
cure-all, vaseline, one of its products, is of great value. It can be
mixed with drugs without changing their character, and it does not
become rancid. For these reasons, salves and other ointments can be
mixed with it and preserved for years.
XI
LITTLE GRAINS OF SALT
The most interesting mine in the world is that of Wieliczka in Poland.
In it there are some thirty miles of streets and alleys; there are
churches with pillars, shrines, and statues; there are stairs,
monuments, and restaurants; there is a ballroom three hundred feet
long and one hundred and ninety feet high, with beautiful chandeliers,
and in it is a carven throne whereon the Emperor Franz Joseph sat when
he visited the mine. There are lakes crossed by ferryboats. There is a
railroad station for the mule trains which bear the precious mineral
salt, for this is a salt mine, and shrines, statues, churches,
chandeliers--everything--are all cut out of salt.
This mine has been worked for at least eight hundred years and still
has salt enough to supply all Europe for ages. The mass of salt is
believed to be five hundred miles long, fifty miles wide, and nearly a
quarter of a mile thick. It is so pure that it is sold just as it
comes from the mine, either in blocks or finely ground. This mine is a
wonderful place to visit, almost like an enchanted palace, for as the
torchlight strikes the crystals of salt, they flash and sparkle as if
the wall was covered with rubies and diamonds.
There is nothing like an enchanted palace in any salt mine of the
United States, no statues or chapels or chandeliers. There is only a
hole in the ground, where mining is carried on in much the same manner
as in other kinds of mines. The shaft is sunk and lined with timbers
to keep the dirt from falling in, just as in other mines. In working
salt mines, however, water is almost as bad as earth, and therefore a
layer of clay is put between the timbers and the earth. There are the
usual galleries and pillars, with roof and floor of salt. The workmen
try to get the salt out in lumps or blocks as far as possible, and so
they bore in drill holes and then blast with dynamite or powder. The
salt is loaded upon little cars, running on tracks, and is carried up
the shaft and to the top of a breaker, usually more than one hundred
feet above the surface of the ground. There it is dumped upon a screen
of iron bars, which lets the fine salt fall through. The large lumps
are sold without crushing or sifting, and are used for cattle and
sheep.
One of the great deposits of salt is in southeastern California. It is
thought that the Gulf of California used to run much farther north
than it now does, and that the earth rose, shutting away part of it
from the ocean. This imprisoned water was full of salt. In time it
dried, and the sand blew over it till it was far underground. A better
way than digging was found to work it, as will be seen later; but
while digging was going on, the workmen built a cottage of blocks of
salt, clear and glassy. The little rain that falls there melted the
blocks only enough to unite them firmly together; and there the house
has stood for many years.
Countries that have no deposits of rock salt can easily get plenty of
salt from the water of the ocean if they only have a seacoast. About
one thirtieth of the ocean water is salt, and if the water is
evaporated, the salt can be collected without difficulty. France makes
a great deal of salt in this way. When a man goes into the
manufacture, or rather, the collecting of salt, he first of all buys
or rents a piece of land,--perhaps several acres of it,--that lies
just above high water, and makes it as level as possible. Unless it is
very firm land, he covers it with clay, so that the water will not
soak through it. Then he divides it into large square basins, making
each a little lower than the one before it. Close beside the highest
basin he makes a reservoir which at high tide receives water from the
ocean. This flows slowly from the reservoir through one basin after
another, becoming more and more salt as the water evaporates. At
length the water is gone, and the salt remains. The workmen take
wooden scrapers and push the salt toward the walls of the basins and
then shovel it up on the dikes and heap it into creamy cones that
sparkle in the sunshine. The dikes are narrow, raised pathways beside
the basins and between them. As you walk along on top of them, you can
smell a faint violet perfume from the salt. Thatch is put over the
cones to protect them from the rain, and there they stand till some of
the impurities drain away. This salt is not perfectly white, because
the workmen cannot help scraping up a little of the gray or reddish
clay with it. Most of it is sold as it is, nevertheless, for many
people have an absurd notion that the darker it is the purer it is.
For those who wish to buy white salt it is sent to a refinery to be
washed with pure water, then boiled down and dried.
So it is that the sun helps to manufacture salt. In some of the colder
countries, frost does the same work, but in a very different manner.
When salt water freezes, the _water_ freezes, but the salt does not,
and a piece of salt water ice is almost as pure as that made of fresh
water. Of course, after part of the water in a basin of salt water has
been frozen out, what is left is more salt than it was at first, and
after the freezing has been repeated several times, only a little
water remains, and evaporation will soon carry this away, leaving only
salt in the basin, waiting to be purified.
Not very many years ago one of the encyclopædias remarked that "the
deposits of salt in the United States are unimportant." This was true
as far as the working of them was concerned, but in 1913 the United
States produced more than 34,000,000 barrels. Part of this was made by
evaporation of the waters of salt springs, and a small share from
Great Salt Lake in Utah. The early settlers in Utah used to gather
salt from the shallow bays or lagoons where the water evaporated
during the summer; but now dams of earth hold back the water in a
reservoir. In the spring the pumps are put to work and the reservoir
is soon filled with water. This is left to stand and give the
impurities a chance to settle to the bottom. Then it is allowed to
flow into smaller basins, while more water is pumped into the
reservoir. When autumn comes, the crop of salt is ready to be
harvested. It is in the form of a crust three to six inches thick,
some of it in large crystals, and some fine-grained. This crust is
broken by ploughs, and the salt is heaped up into great cones and left
for the rain to wash clean. Then it goes to the mill for purifying.
The water of Great Salt Lake is much more salty than that of the
ocean. It preserves timber remarkably well, and often salt from the
lake is put around telephone poles, seventy-five pounds being dropped
into the hole for each one. It has been suggested to soak timber in
the Lake, and then paint it with creosote to keep the wet out and the
salt in.
Salt is also made from the waters of salt springs, which the Indians
thought were the homes of evil spirits. At Salton, in California, an
area of more than one thousand acres, which lies two hundred and
sixty-four feet below sea level, is flooded with water from salt
springs. When this water has evaporated, all these acres are covered
with salt ten to twenty inches thick, and as dazzlingly white as if it
was snow. This great field is ploughed up with a massive four-wheeled
implement called a "salt-plough." It is run by steam and needs two men
to manage it. The heavy steel ploughshare breaks up the salt crust,
making broad, shallow furrows and throwing the salt in ridges on both
sides. The plough has hardly moved on before the crust begins to form
again. This broken crust is worked in water by men with hoes in order
to remove the bits of earth that stick to it, then piled up into cones
to drain, loaded upon flat trucks, and carried to the breaker. The
salt fields are wonderfully beautiful in the moonlight, but not very
agreeable to work in, for the mercury often reaches 140° F., and the
air is so full of particles of salt that the workers feel an intense
thirst, which the warm, brackish water does not satisfy. The work is
done by Indians and Japanese, for white people cannot endure the heat.
A large portion of the salt used in the United States comes directly
from rock salt strata, hundreds of feet below the surface of the
ground. These were perhaps the bed of the ocean ages and ages ago.
There is a great extent of the beds in New York, Michigan, Ohio,
Kansas, and other States. In Michigan there is a stratum of rock salt
thirty to two hundred and fifty feet thick and some fifteen hundred to
two thousand feet below the surface. To mine this would be a difficult
and expensive undertaking, and a far better way has been discovered.
First, a pipe is forced down through the surface dirt, the limestone,
and the shale to the salt stratum. The drill works inside this pipe
and bores a hole for a six-inch pipe directly into the salt. A
three-inch pipe is let down inside of the six-inch pipe, and water is
forced down through the smaller pipe. It dissolves the salt, becomes
brine, and rises through the space between the two pipes. It is
carried through troughs to some great tanks, and from these it flows
into "grain-settlers," then into the "grainers" proper, where the
grains of salt settle. At the bottom of the grainers are steam pipes,
and these make the brine so hot that before long little crystals of
salt are seen floating on the surface of the water. Crystals form much
better if the water is perfectly smooth, and to bring this about a
very little oil is poured into the grainer. It spreads over the
surface in the thinnest film that can be imagined. The water
evaporates, and the tiny crystals grow, one joining to another as they
do in rock candy. When they become larger, they drop to the bottom of
the grainer. They are now swept along in a trough to a "pocket,"
carried up by an endless chain of buckets, and then wheeled away to
the packinghouse.
The finest salt is made by using vacuum pans. These are great cans out
of which the air is pumped, and into which the brine flows. This
brine, heated by steam pipes, begins to boil, and as the steam from it
rises, it has to pass through a pipe at the top and is thus carried
into a small tank into which cold water is flowing. The cold makes the
steam condense into water, which runs off. The condensed water
occupies less space than the steam and so maintains the vacuum in the
pan. For a perfect vacuum the brine is boiled at less than 100° F.,
while in an open pan or grainer it requires 226° to boil brine. The
brine is soon so rich in salt that tiny crystals begin to form. These
are taken out and dried. If you look at some grains of table salt
through a magnifying glass, you can see that each grain is a tiny
cubical crystal. Sometimes two or three are united, and often the
corners are rounded off and worn, but they show plainly that they are
little cubes.
Most of the salt used on our tables is made by the vacuum process or
by an improved method which produces tiny flakes of salt similar to
snowflakes. The salt brine is heated to a high temperature and
filtered. In the filters the impurities are taken out, and this
process gives us very pure salt. The tiny flakes dissolve more easily
than the cubes of salt, and thus flavor food more readily.
With a few savage tribes salt is regarded as a great luxury, but with
most peoples it is looked upon as a necessity. Some of the early races
thought a salt spring was a special gift of the gods, and in their
sacrifices they always used salt. In later times to sit "above the
salt," between the great ornamental salt cellar and the master of the
house, was a mark of honor. Less distinguished guests were seated
"below the salt." To "eat a man's salt" and then be unfaithful to him
has always been looked upon as a shameful act; and with some of the
savages, so long as a stranger "ate his salt,"--that is, was a guest
in the house of any one of them,--he was safe. To "eat salt together"
is an expression of friendliness. Cakes of salt have been used as
money in various parts of Africa and Asia. "Attic salt" means wit,
because the Athenians, who lived in Attica, were famous for their
keen, delicate wit. To take a story or a statement "with a grain of
salt" means not to accept it entirely, but only to believe it
partially. When Christ told his disciples that they were "the salt of
the earth," he meant that their lives and teaching would influence
others just as salt affects every article of food and changes its
flavor. Our word "salary" comes from the Latin word _sal_, meaning
salt; and _salarium_, or "salt-money," was money given for paying
one's expenses on a journey. Living without salt would be a difficult
matter. Cattle that have been shut away from it for a while are almost
wild to get it. Farmers living among the mountains sometimes drive
their cattle to a mountain pasture to remain there through the summer,
and every little while they go up to salt the animals. The cattle know
the call and know that it means salt; and I have seen them come
rushing down the mountain-side and through the woods, over fallen
trees, through briers, and down slippery rocks, bellowing as they
came, and plunging head first in a wild frenzy to get to the pieces of
rock salt that were waiting for them.
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