Produced by Diane Monico and The Online Distributed
Proofreading Team at https://www.pgdp.net (This file was
produced from images generously made available by The
Internet Archive/American Libraries.)
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 deg. or
3000 deg.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 deg. 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 deg. 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.