[Illustration: A CONCRETE ROAD
Our two last pictures relate to an exceedingly important and rapidly
increasing use of cement. It is the construction of concrete roads.
The first picture shows a concrete road in course of construction.
The mechanical mixer referred to above is shown in this picture. It
is a self-propelling machine and mixes the concrete very rapidly. As
it comes from the mixer in a wet and mushy mass it is placed between
rigidly staked side forms, where it hardens into imperishable rock.
The road is brought to its shape by working to and fro a long plank
called a template, after which the surface of the road is troweled with
wooden floats, giving it a texture which prevents horses and cars from
slipping. The last picture shows a narrow concrete road in the state of
Maryland. Wherever these roads have been built they mean much to the
women and children of the community. They never grind up into mud or
dust, and are as pleasant to walk upon as the sidewalks of the city.
Children, especially, delight in them. In Wayne county, Mich., where
they have the most celebrated concrete roads in the world, the children
go to and from school on roller skates, and various games are played on
the concrete road.]
Why Don’t We Make Roads Perfectly Level?
Roads are made with a curving upper surface, i. e., higher in the
middle, in order that the rain will drain away from the road into the
gutters or ditches which you find at the sides. You see water has the
faculty of running only in one direction, and that is downward. If it
cannot go down on one side or the other, it will collect in puddles
and make the road impassable. For this reason we build our roads so
they are higher in the middle than at the sides--not much higher; only
about six inches or so--giving them just the gentle slope toward each
side that is necessary to allow the water to run off gradually, but
sufficiently sloping to keep the water from collecting in puddles in
the road. Thus after the dust has been settled by the first rain that
falls, most of the surplus rain that falls on the roads finally runs
into the ditches at the side of the road.
Why Are Some Roads Called Turnpikes?
Undoubtedly the name turnpike as applied to some roads arose from the
fact that pikes or gates were set across the roads by the keeper or
toll-collector. In addition to collecting tolls, it was a part of the
toll-keeper’s business to keep the road in repair. His wages and other
expenses for doing this were received from the tolls collected from the
people who used the road to ride on in carriages, wagons, etc. In the
early days the toll-collector was armed with a pike, a long-handled
weapon with a sharp iron head, which he used to prevent people who
travelled his road from going by without giving up their toll. Later on
a swinging gate was built across the road, which made it unnecessary to
use the pike, though the name was retained, for no one could pass while
the gate barred the way. When the passerby had paid his tolls, the
toll-collector opened the gate and let him pass. If he did not pay the
gate remained closed and the driver had to turn back or decide to pay.
Hence comes the name turnpike. In some parts of the country they call
these toll roads.
What Is Dust?
A large part of the dust we see in the roadway when the horses kick it
up, or when an automobile passes, is made up of the pulverized dirt of
the roadway. It becomes mixed with other things, such as the street
deposits of animals, particles of carbon, etc. Particles of this dust
get into our throats, and as there are many germs in it, they are very
liable to cause sickness, especially the colds from which we suffer.
What Becomes of the Dust?
The dust of the roadway is generally blown away by the wind, to come
down to earth again wherever the wind happens to carry it--on the
lawns, the doorsteps or back to the road, perhaps. In any event, the
rain which is certain to come sooner or later, washes this dust back
into the soil, or into the sewers. Part of it mixes with the soil. The
organic matter in dust helps to fertilize the soil, and is therefore
useful. Other parts of the dust are oxidized and consumed by the
air, through the heat of the sun. So you see the dust is continually
changing from one thing to another.
Are Stones Alive?
Real stones are not alive. They do not become stones until they have
been burned out--until they have become what is known as dead matter.
This is meant entirely in the sense that we commonly think of the
meaning of the word “alive,” which is to be able to breathe and grow.
Stones can neither breathe nor grow. They belong to the inanimate
kingdom of things on the earth. Particles of this dead matter, found in
stones, etc., are in many cases taken up by things that are actually
alive, and help to form the bodies of living things.
The most common thing to be found in rocks and stones is what is
called “silicon,” and we find this silicon in the straws of the wheat,
oats and corn, and in many other things, but not in a way that can be
detected except by chemical analysis. A great many of the things found
in stones are found in living things, but rocks and stones are not
alive in any sense.
What and Why Is Smoke?
Smoke is produced only when something which is being burned is burning
imperfectly. If we were to put anything burnable into the fire and
establish just the right amount of draft, and knew how to build our
fires properly, there would be no smoke and very little ashes.
In the case of the black coal smoke which we think of mostly when
we think of smoke at all, the black portion is principally little
unburned particles of coal which pass up the chimney with the gases
which are thrown off when the coal is being burned. These gases would
be invisible--they really are invisible--if it were not for the little
particles of coal which are drawn up the chimney with them. If you look
at the chimney from which a wood fire expels the gases you find the
smoke very light in color--showing that not so much unburned matter is
being thrown off. A charcoal fire makes no smoke, because the charcoal
has had the unburnable things taken out of it beforehand, and the
charcoal stove is almost perfect in construction from the standpoint of
combustion.
Of course, the thickness of the smoke from a coal fire is often
increased by the fact that there are unburnable things mixed in with
the coal, some of which also pass off through the chimney.
Why Can’t We Burn Stones?
We cannot burn anything that has already been burned, and a stone has
already been burned. To understand how this is we must first find out
what takes place when a thing is burned. When a thing is burning it
means merely that that particular thing is taking into its system all
of the oxygen of the air that it can combine with. When it has done
this it cannot be burned any more. Of course, in doing this the thing
originally burned changes its character. The elements in a candle when
lighted mix with the oxygen in the air and disappear in the form of
gases. The elements in coal mix when fired with oxygen and change into
ashes, gases and smoke. A stone, however, is the result of a burning
that has already taken place. The original element of most of the rocks
and stones we see was silicon, and when that combines with oxygen,
the result is some form of rock, which you may be able to break up or
throw, but which you cannot burn again.
What Is Fog?
The fog which we generally think of when we speak this word is the
fog at or on the sea or other body of water--the one that makes the
ships stand by and blow their fog horns. A fog of this kind is nothing
more nor less than a cloud, come right down to earth and spread out a
little more. People who have gone up into the air in balloons and other
airships through the clouds, say that the clouds are only fogs, and
that above them it is as clear as it is on a sunshiny day on the water
when there is no fog.
There is another kind of fog which settles down over the land,
especially in the cities. It is a damp mist which combines with the
smoke and other impurities in the air and forms a black and dirty cloud
about everything. This occurs when the upper air prevents the smoke
which rises from a city with all its people and fires in the furnaces
from passing up and away. The upper air acts like a blanket and keeps
the misty, smoky air down, until the wind comes along and blows it away.
What Becomes of the Smoke?
There are a number of things in smoke, and when we know what they are,
we will find a natural answer to this question. First, there are, of
course, the little unburned particles of fuel which get carried up
the chimney by its drawing power. These naturally fall to the ground
of their own weight, once they get beyond the drawing power of the
chimney and out of the current of air so formed. Some of the gases
are already quite burned out when they pass up the chimney. There is
a lot of carbonic acid gas which, of course, mixes with the air and
eventually becomes food for the plants. Then there are some gases which
are not entirely burned, and the air burns them still more until they,
too, become carbonic acid gas, or water which is also thrown off by a
burning fire.
Why Does an Apple Turn Brown When Cut?
The reason is that when you cut an apple, the exposure to the air of
the inside of the apple causes a chemical change to take place, due to
the effect the oxygen in the air has on what is scientifically known as
the enzymes in the apple, or what are commonly called the “ferments.”
When the peel is unbroken it protects the inside of the apple against
this action by the oxygen. The brown color happens to be due to the
chemical action. The action is similar to the action of the air on wet
or damp iron or steel, in which case we call it rust.
Why Does a Piece of Wood Float in Water?
A piece of wood will float in water because it is lighter than the
same amount of water. We do not mean that a piece of wood weighing one
pound, for instance, would weigh any more than a pound of water, of
course, but if you took the measurements of each you will find that
it took less bulk to make a pound of water than of wood. If you had a
piece of wood so shaped that it just filled a glass completely, and
then took another glass and filled it with water, you would find that
the glass containing the water weighed the most. Another name to give
to this difference would be to say that the water was more dense than
the wood. By the law of gravitation the denser thing will always go
to the bottom, and as wood is less dense than water, it will stay at
the top if put in water. The piece of wood has more air in it than the
water. If you could expel the air from the piece of wood and then put
it in water, it would sink.
Why Does Iron Sink In Water?
The explanation in regard to the piece of wood floating in water is the
beginning of the answer to this question. A piece of iron is heavier
than an equal bulk of water, and will therefore go to the bottom, as
will all things which are more dense than water. A piece of iron has no
air in it. The particles of a piece of iron are so close together that
there is no room for air in it and it will therefore sink in water. A
piece of wood from which all of the air had been expelled would also
sink.
Why Doesn’t an Iron Ship Sink?
This is a very natural question for you to ask right after you were
told why iron sinks in water. The explanation is that by making an
iron ship in the way we do, we fix it so that it holds a lot of air in
between the bottom and sides, making the combination of the two--the
iron ship and the air in it--lighter than the water on which it sails.
Men thought at one time that a ship would sink if made of iron, and
therefore built all of their ships of wood. Finally one inventor made a
ship of iron and it was one of the wonders of the world. When we found
that iron ships would float if they were built to retain sufficient air
to keep them from sinking, we made the hulls of most ships of iron for
a time. Now, however, the best ships are made of steel, which is even
better.
If you bore a hole in the bottom of a ship, the water will run in if
the ship is in the water, and the ship will sink, because the water
coming in drives out the air; and when the ship is full of water,
the water in it, with the ship itself, are heavier than the water on
which it sails, and the ship will go down. Filling a ship with water
makes the iron part of the ship just like a bar of iron, so far as its
sinking qualities are concerned.
Of course, an iron ship must be made long enough and broad enough so
that when it is completed there will be sufficient air contained within
the hull to make the combination lighter than water. Always, therefore,
when a ship is to be built, competent engineers must go over the plans
of the vessel and calculate the air capacity, so as to make sure she
will float.
Nowadays it would be difficult to sink a modern vessel by boring one
small hole in the bottom, because the bottom and sides are lined with
enclosed steel air-chambers, and a ship will keep afloat even if one
or a number of holes are made. The reason is, of course, that when you
bore a hole into one of these air-chambers the water rushing in will
fill that air-chamber with water, but as there is no connection from
the inside with the rest of the ship, the water can get no further.
Why Does a Poker Get Hot at Both Ends if Left in the Fire?
Both ends of the poker become heated because the poker is made of iron,
and iron is a particularly good conductor of heat. To understand this
we must look into the question of what a good conductor of heat is.
In this case the particles of iron, which combined form the poker,
are so close together that when those at the end of the poker which
is in the fire get hot, the particles at that end hand the heat on to
the particles next to them, and so on until the whole poker is hot.
The difference between a thing which is a good conductor of heat and
a thing which is not a good conductor, lies in the ability of the
different particles which compose it to hand the heat on to the others.
Did you ever notice that the handle of a solid silver spoon will
become hot if the spoon is left in hot coffee? Solid silver is a good
conductor of heat. A plated spoon is not a good conductor, however, and
will not become hot if left in the cup of hot coffee as a solid silver
spoon will.
Would a Wooden Spoon Get Hot?
A wooden spoon would not get hot, because wood is not a good conductor
of heat. The atoms which compose the wood have not the power to
transmit the heat to each other. This is strange, too, when we think
that a poker is a good conductor of heat, but will not burn, while
wood is not a good conductor, but will burn readily. Perhaps you have
already discovered this in connection with a wood fire. One end of a
stick of wood may be burning fiercely, and yet you can pick it up by
the other end and find it is not even warm. This proves to you that
wood is not a good conductor of heat, and explains why the handle of a
wooden spoon in a bowl of hot soup will not get hot while the handle of
a silver spoon will.
Why Does Iron Turn Red When Red Hot?
The answer is that the piece of iron has been heated to the point where
it gives off light of its own. The red you see is only one stage in
the development of iron to the point where it makes its own light. If
you heat it still more it will make a white light. You know that it
produces the light itself, because if you take a piece of iron into a
perfectly dark room and heat it to a white heat it will show better
than where there is other light. If you continue the process the iron
will melt and change in form. Therefore, the “red hot” name for a piece
of iron in that state is a perfect name. It is a warning that the iron
is coming to a point where if the heating process is continued, it will
change its form and in this state, when treated according to known
methods, the iron is turned into steel, which has many characteristics
that iron does not possess. Now, I can, of course, hear you ask why
doesn’t an iron kettle get red hot? and I can answer that easily. If
you treat the kettle the same way as you do the piece of iron, it
will get red hot. The difference is that you are thinking of an iron
kettle with water in it. As long as there is any water in the kettle,
that keeps it from getting hot. The water inside keeps the kettle from
becoming red hot. If you took a hollow rod of iron and filled it with
water, it would not become red hot as long as any water remained in the
hollow portion.
How Did the Sand Get on the Seashore?
The sand on the seashore is nothing more or less than ground-up
sandstone. In dealing with the inanimate things in the world we find
that a very important element of all of them has been given the name
silicon. When the crust of the earth, which is the part we call the
land and rocks, and includes the part under the sea, was a molten mass,
this silicon was burned, combining with the oxygen which surrounded
everything, and produced what is known as silica. Silica is the name
given to the thing which is left after you burn silicon. A very large
part of this silica was deposited in parts of the earth, and when the
crust of the earth cooled off it was sand. By pressure and contact with
other substances it became stuck together, just as you can take wet
sand at the seashore to-day and make bricks and houses and tunnels,
excepting that in the case we speak of it was something besides water
that pressed and stuck the little particles of sand together. They
stuck together more permanently. Then when the oceans were formed, as
shown in another part of this book, much of the sandstone was found to
be at the bottom and on the shores of the oceans. The action of the
water continually washing against the sandstone gradually broke the
sandstone up into the tiny particles of sand again, and this is what
makes the sand on the seashore.
What Makes a Soap Bubble?
A bubble is merely a hollow ball of water with air inside. The air
in coming up through the water in trying to rise out of the water is
caught in the water in such a way as to form the bubble, and since the
ability of the air inside of the bubble to rise is greater than that of
the water which forms the bubble, and which has a tendency to pull it
down, the bubble rises into the air. The water ball is very thin and
keeps running down to the bottom of the ball, where you see it form
into drops, and soon this makes the walls of the water bubble so thin
that the air bursts through the ball of water, and that is
What Makes the Bubble Explode?
Sometimes we blow soap bubbles. We mix soap in the water and that makes
the walls of the water ball which we produce a little tougher, and it
requires a great deal more effort for the air to escape from it, as the
soap keeps the water in the walls of the bubble from running down to
the bottom for quite some time, and, therefore, soap bubbles will often
travel in the air for some distance. The colors we see on soap bubbles
are produced by the rays of sunlight, which strike the bubble and
reflect them back to us in colors very similar to those of the rainbow.
Why Are Bubbles Round?
Bubbles are round because the air which forms the inside of the bubble
exerts an equal pressure in all directions. It presses equally against
all sides of the bubble at the same time.