This picture shows the depth to which the pipes which carry the water
through the city must sometimes be sunk in order that it will be
certain to remain in place. To illustrate this in connection with the
depth of the water tunnel in one place in the city of New York, our
artist has taken the liberty of turning the Woolworth Building upside
down. Even this building, which is the tallest business building in the
world, and is 792 feet high, would not penetrate the water tunnel, at
the point shown, which is at the Clinton Street shaft at the west bank
of the East River.]
What is Carbonic Acid?
It was formerly called fixed air, and is a gaseous compound of
carbon and oxygen. It is procured by the processes of combustion and
respiration, and hence is always present in the air, though in minute
quantity. Plants live upon it and absorb it into their tissues; they
abstract and assimilate its carbon, and return its oxygen to the
atmosphere in a pure condition. It is also present in spring water,
and often in quantities, so that it sparkles and effervesces; it is
also produced during the processes of putrefaction, fermentation, and
slow decay of animal and vegetable substances in presence of air. It
is largely employed by the manufacturers of aerated bread and aerated
waters. Under a pressure of about 600 pounds it liquefies, and when
allowed to escape through a small jet it rapidly evaporates and causes
intense cold, so much so as to become frozen. It does not support
burning. The gas derived from it, carbon dioxide, is invisible, and
is heavier than air by one half, and has a pungent odor and slightly
acid taste. In a pure state the gas cannot be respired, as it supports
neither respiration nor combustion. When the portion in the atmosphere
is increased to a considerable extent, as happens sometimes, it
endangers life. The familiar “rising” of bread is brought about by
carbonic acid gas escaping through and permeating the dough, making
it light and porous. In this form it is known as yeast or as baking
powder. We see its uses also in the chemical fire-engine.
In some parts of the world large quantities of carbonic acid gas are
constantly issuing from openings of the earth’s surface. Two such
places are the famous Poison Valley of Java, and the Grotto del Cane,
near Naples, in Italy. The former is a small valley about a half a mile
around and about thirty-five feet deep, in which the air is so loaded
with carbonic acid gas that animals entering it are killed in a few
minutes. Even birds that fly over the valley are overcome if they do
not rise high above it. The Grotto del Cane, or Grotto of the Dog, is
a small cavern in the crater of a volcano. A stream of carbonic acid
gas flows constantly into the grotto, but the level of the gas does not
reach the height of a man’s mouth. When the same air is breathed over
and over again, the quantity of carbonic acid in it is increased so
much, that it may become as deadly as the air in the Poison Valley.
Two other gases that may generally be found in air are ozone and
ammonia. The first is merely a form of oxygen that is produced by the
passage of lightning through the air. After severe thunderstorms, it is
said to be present, sometimes, in sufficient proportion to give to the
air a slightly pungent odor. It is more active chemically than is the
ordinary form of oxygen, and consequently has a stimulating effect upon
animals.
Ammonia, or hartshorn, as it is sometimes called, from the fact that
it was formerly obtained by distilling the horns of harts, or deer, is
almost always present in the air in small quantities. It is produced
chiefly by the decay of animal and vegetable matter, especially the
former. Though present in the air in very small quantities, it is of
much value to the plant world, because it contains nitrogen in a form
in which it can be readily absorbed by plants. All plants contain some
nitrogen, which is essential to their growth, but the greater part of
the nitrogen in the air is not in such form that it can be absorbed
by them. They must obtain their supply from the soil, which usually
contains some nitrogen in a form that may be taken up by plants, and
from the ammonia in the air. The latter is not taken directly out of
the air by the plants, but the rains falling through the air absorb the
ammonia and carry it to the soil, from which it is taken up into the
plants by their roots.
~VARIOUS GASES FOUND IN AIR~
Besides the gases that have been mentioned, there is present in the
air, at all times, a small quantity of water-vapor, which is, in many
ways as important to mankind as is the oxygen itself. The quantity
of water in the air is not always the same. As a rule, the quantity
is greater in warm air than in cold, and is less over land than over
water. Frequently the air feels damp in cold weather, and dry in hot
weather, and it is natural to suppose that there is more vapor in the
air on the damp day than on the dry one. This, however, is not always
true. There is usually more moisture in the air on a warm summer day
than on a cold day in winter, though the winter day may seem much more
moist. You will be able to understand why this is so by comparing the
air to a sponge. If we fill a sponge with water, and squeeze it gently,
a little water will be forced out of it. If we then remove the pressure
on the sponge. When the air cools, will appear dry on the surface, but
there will still be water in it, and on being squeezed harder than
before it will again become moist on the surface and more water will be
forced out of it. Now cold has an effect upon moisture-laden air very
much like that of pressure on the sponge. When the air cools, some of
the moisture is forced out of it, and the air seems damp. When it warms
again, the air seems dry, though there is still water-vapor in it. It
seems dry because it can absorb more water-vapor, just as the sponge
seems dry after you cease to squeeze it, though it still contains
water. From this we see that the air does not always seem moist when
there is much water-vapor in it, nor dry when there is only a little.
It feels moist when there is as much water-vapor present as it can
hold, and dry when it can held more than it already has. And we also
see that in hot weather the air can hold much more moisture than it can
in cold weather, so that whether the air feels dry or moist, there is
generally much more water-vapor in it in hot weather than in cold.
It is easy to see that, over water, the air naturally takes up more
moisture than over land, because there is so much more water there to
be transformed into vapor. Over the surface of seas, lakes and rivers,
water is continually being converted into vapor by the process of
evaporation, and this vapor is absorbed by the air.
Let us now consider the solid particles floating in the air, the dust
that is seen dancing in the path of a sunbeam. Whenever we examine the
air, these small particles are found, even on the tops of mountains,
and at points so high above the earth that they have been reached only
by balloons. Of course, there is very much less dust high above the
earth than near the surface, where the winds are constantly stirring
up the loose soil, and throwing into the air small particles of every
kind. In cities, where factory chimneys are continually pouring out
clouds of smoke, and the people and vehicles are constantly disturbing
the dust of the streets, the air always contains more dust than does
the air of the country.
In order that we may breathe air, the oxygen in it has been mixed with
four times as much nitrogen and argon, which must be inhaled with the
oxygen, though they have no more effect on the body than the water
you take with a strong medicine to weaken it. The oxygen, however,
has a very important effect upon the body, and if we compare the air
we exhale with that we inhale we find considerably less oxygen in
the former than in the latter. In place of the oxygen, the air has
received carbonic acid gas. It may seem very strange to say that there
is burning going on in the body, but that is very nearly what takes
place. The chief difference from coal-burning is that in the body the
process goes on so slowly that it does not make the body very hot;
but when we set fire to coal, the process is much more rapid, and a
large amount of heat is produced in a short time, so that the coal
becomes very hot. The products of breathing and of coal-burning are the
same, carbonic acid gas being the chief one. When coal is burned it
disappears, together with some of the oxygen of the air, and in their
stead we have carbonic acid gas. When a breath is taken some of the
material of the body disappears, as does some of the oxygen of the air,
and in place of them carbonic acid gas is found. If we could weigh the
coal burned and the oxygen that disappears in the burning of it, and
could then weigh the carbonic acid gas that is produced in the burning,
we should find that the latter weighs just as much as the coal and the
oxygen together. So, too, if we could weigh the oxygen that disappears
from the air we breathe, and also find the weight of the material taken
from our bodies by breathing, we should find that the two together
weigh just as much as the carbonic acid gas given off in our breath. In
neither case is anything absolutely destroyed; the substances resulting
from the change weigh just as much as those that took part in it.
Having learned that a quantity of oxygen disappears every time we
take a breath, every time we build a fire, it would seem that in the
thousands of years during which men and animals have been living on the
earth, all the oxygen would have been exhausted and nothing left in
its place but carbonic acid gas. That, however, is impossible, as the
carbonic acid gas is used up almost as fast as it is produced and the
oxygen is returned to the air in its stead.
~HOW PLANTS EAT CARBONIC ACID~
All trees and plants, from the great redwood trees of California to the
smallest flowers that dot the fields, need carbonic acid gas to keep
them alive and to make them grow. Their leaves have the power when the
sun shines on them to take up carbonic acid from the air and to return
oxygen in exchange. In this way you see that the balance is kept just
as it should be. The oxygen needed by animals of all kinds is furnished
by the plants, and the carbonic acid required by plants is thrown off
in the breath of animals.
Is It a Fact that the Sun Revolves On Its Axis?
It is a proved fact that the sun revolves on its axis. All parts of its
surface, however, do not rotate with the same velocity. The rotation of
the sun differs from that of the earth in this respect.
This constitutes the visible proof that the physical state of the sun
is different from the earth’s, although they are composed of similar
chemical elements.
The earth, being covered with a solid crust, and being also, as recent
investigation demonstrates, as rigid as steel throughout its entire
globe, rotates with one and the same angular velocity from the equator
to the poles.
If you stood on the earth’s equator you would be carried by its daily
rotation round a circle about 25,000 miles in circumference. If you
stood within a yard of the North or South Pole you would be carried, by
the same motion, round a circle not quite 19 feet in circumference. And
yet it would require precisely the same time, viz., twenty-four hours,
to describe the 19-foot circle as the 25,000-mile one.
What Is the Most Usefully Valuable Metal?
If you were guessing you would naturally say that gold is, of course,
the most valuable of the metals. But you would be wrong. The proper
answer to this is iron. We do not mean the pound for pound value, for
you could get much more money for a pound of gold than for a pound
of iron, but we mean in useful value--iron is in that sense the most
valuable metal known to man. This is so because iron is of great
service to man in so many different ways, and it is very well that
there is so great a quantity of it for man’s use.
[Illustration: WHERE DOES TOBACCO COME FROM?