How Did the Coal Get Into the Coal Mines?
The heavy black mineral called coal, which we burn in our stoves
and furnaces, and use to heat the boilers of our engines was formed
from trees and plants of various sorts. Most of the coal was formed
thousands of years ago at a time when the atmosphere that envelopes the
earth contained a much larger proportion of carbonic acid gas than it
does now, and the climate of all regions of the earth was much warmer
than it now is. This period was known as the carboniferous age, that
is, the coal-making age, and its atmospheric conditions, favored the
growth of plants, so that the earth was covered with great forests,
of trees, giant ferns, and other plants, many of which are no longer
found on the earth. In the warm, moist, and carbon-laden atmosphere of
that period the growth of all kinds of plants was rapid and luxuriant,
and as fast as old trees fell and partially decayed, others grew up in
their places. In this way, thick layers of vegetable matter were formed
over the soil in which the plants grew. In many places, where these
beds were formed, the surface of the earth became depressed and the
water of the sea flowed over the beds of vegetable matter.
Sediment of various kinds was deposited over the vegetable matter, and
in the course of centuries the sediment was transformed into rock.
After the formation of the covering of sediment, the decay of the
vegetable matter was checked, but a slow change of another kind was
brought about by the pressure of the sedimentary deposits and the heat
to which the plant remains were subjected. The hydrogen and oxygen
which constituted the greater part of the plant substance was driven
off and the carbon left behind. This change took place very gradually,
through periods so long that we can only guess at their duration, but
we know that many beds of coal were formed from layers of vegetable
matter that were covered up many thousand years ago.
[Illustration: MINE WORKERS THAT NEVER SEE DAYLIGHT
Underground stable constructed of concrete and iron, with natural rock
roof to avoid danger of fire. Mules are only taken to surface when
mines are idle.]
The coal first formed and submitted longest to pressure is known as
hard coal, or anthracite. It is pure black, or has a bluish metallic
luster. Its specific gravity is 1.46; which is about the same as that
of hard wood. Anthracite contains from 90 to 94 per cent. of carbon,
the remainder being composed of hydrogen, oxygen, and ash.
[Illustration: The Mules and their drivers.--An important part of the
haulage system. Mules are kept in stables on surface at this mine and
driven in every day through slope or drift.]
Hard coal may be called the ideal fuel and is especially adapted to
domestic heating purposes. It burns without smoke and produces great
heat. There is no soot deposit upon the walls of chimneys, and in good
stoves or furnaces the small amount of gas given off by it is consumed.
Anthracite is the least abundant of all the varieties of coal and is
much more costly than the other varieties. For this reason it is not
much used in manufacturing.
[Illustration: HOW THE SLATE PICKERS WORK
Boy slate pickers. Coal slides down the chutes. Boys pick out the slate
and rock and throw into chute alongside.]
[Illustration: Spiral slate pickers do work of many boys. Coal and rock
start together at the top in the small inner spiral. The coal being
lighter slides faster, and in going around is carried over the edge
into the outer spiral, while the rock continues in the bottom.]
The coal formed later is very different in composition and is called
bituminous or soft coal. Its name is derived from the fact that it
contains a soft substance called bitumen, which oozes out of the coal
when heat is applied to it. Soft coal contains from 75 to 85 per cent.
of carbon, some traces of sulphur, and a larger percentage of oxygen
and hydrogen than anthracite. When soft coal is heated in a closed
vessel or retort, the hydrogen and oxygen, in combination with some
carbon, are driven off.
[Illustration: HOW A COAL MINE LOOKS INSIDE
Shaft gate. One of the two cages in the shaft has just brought the men
to the surface; the other is at the bottom. Safety gate resting on top
of cage covers top of shaft when cage is down, as shown at right.]
[Illustration: Section showing Anthracite Seams. Coal is shown black;
rock and dirt lighter; shaft tunnels and workings, white. Upper part of
“Mammoth” seam is stripped and quarried.]
[Illustration: Lignite mine in Texas. Loaded mine cars ready to go to
surface.]
[Illustration: HOW THE MINERS LOOSEN THE COAL
Undercutting with pick. The man lying on his side cuts under the coal.
A light charge of powder exploded in a drill hole near the roof breaks
the coal down in large pieces.]
Soft coal is black, and upon smooth surfaces it is glossy. It lacks the
bluish luster sometimes seen in hard coal and is much softer and more
easily broken. When handled it blackens the hands more than hard coal
does. In this kind of coal are frequently seen the outlines of leaves
and stems of plants that enter into its formation. Occasionally, trunks
of trees with roots extending down into the clay below the bed of coal
have been found.
[Illustration: Undercutting in seam. A compressed air driven machine
undercuts deeper and faster than the man with a pick.]
Soft coal has a specific gravity of 1.27. It burns with a yellow flame
which is larger than the flame from hard coal, but it does not emit so
high a degree of heat. Combustion, generally imperfect, gives rise to
offensive gases and to black smoke that concentrates in the air and
falls to the ground as soot, which blackens buildings, and, in winter,
noticeably discolors the snow.
The formation of lignite has been observed in the timbers of some
old mines in Europe. In some of these mines wooden pillars have been
supporting the rocks above for four hundred years or longer, and in
that time the pressure of the rocks and other influences acting upon
the wood of the pillars have caused it to become transformed into a
brown substance resembling lignite. This fact tends to confirm the
theory of coal formation stated at the beginning of this article. The
proportion of carbon in lignite is never above 70 per cent., and the
ash indicates the presence of considerable earthy matter. It is chiefly
used in those forms of manufacture where a hot fire is not required. In
Europe it is used, to some extent, in heating the houses of the poorer
classes.
Peat is regarded as the latest of the coal formations. In it, the
change in the vegetable matter has not extended beyond merely covering
it, and subjecting it to slight pressure.
Peat is formed in marshy soils where there is a considerable growth
of plants that are constantly undergoing partial decay and becoming
covered by water. It consists of the roots and stems of the plants
matted together and mingled with some earthy material. When freshly
dug out of the bog or marsh in which it was formed there is always a
quantity of water in it, the amount being greatest in the peat found
nearest the surface and least in that at the bottom of the bed, where
the peat is not very different in appearance from lignite.
Peat is used for fuel where wood is scarce and coal is high in price.
Recent experiments in saturating peat with petroleum, have shown that
in this way a form of fuel may be produced for which considerable value
is claimed. Its manufacture is confined to Southern Russia, where peat
is plentiful and petroleum is cheap.
Why Does Firedamp Explode in a Safety Lamp Without Producing an
Explosion of the Gas With Which the Lamp Is Surrounded?
The passing of the flame from the lamp to the outside air is prevented
by the gauze. This splits the burning gas into little streamlets (784
to each square inch of gauze), which are cooled below the point of
ignition, that is, are extinguished by coming in contact with the metal
of the gauze, so that the flame does not pass outside the lamp. In some
cases the explosion may be so great as to force the flame through the
gauze and thus ignite the gas outside.
Are There Any Conditions Under Which it Would Not Be Safe to Use a
Safety Lamp?
~THE DANGERS TO THE MINERS~
The underground conditions affecting the safety of the lamp are
exposure in air-currents of high velocity by reason of which the flame
may be blown through or against the gauze, or exposure for too great
a time to mixtures of air and gas which will burn within the lamp and
thus heat the gauze. The dangerous velocity of air-currents begins at
about 500 feet a minute, but varies with the type of lamp, some being
much less sensitive to air-currents of high velocity than others. Other
conditions under which the lamp is not safe concern the lamp itself or
the one using it. The lamp is dangerous in the hands of inexperienced
persons or when the gauze is dirty or broken. If the gauze is dirty,
that portion absorbs the heat and may become hot enough to ignite the
outside gas; naturally any holes in the gauze will pass the flame.
The safety lamp when left too long in air containing much explosive gas
may cause an explosion, and it is extinguished by certain unbreathable
gases. The electric lamp burns safely regardless of the atmosphere,
but gives no warning of poisonous or explosive gases. It is often used
by rescue men wearing oxygen helmets to enter mines full of poisonous
gases after explosions.
[Illustration: THE LAMP WHICH SAVES MANY LIVES
The safety lamp. The sheet iron bonnet or covering of the upper part
protects the gauze within from strong currents of air, while the glass
permits the light to be diffused. The above is a modern lamp similar to
a bonnetted Clanny lamp.]
The safety lamp is dangerous when there is a hole in the gauze that
will permit the passage of flame to the outside, or when the gauze
is dirty, so that any particular spot may be overheated, or when the
velocity of the air is so great that the flame is blown through the
gauze, or (generally) when in the hands of an inexperienced person. The
unbonneted Davy lamp is not safe where the velocity of the air exceeds
360 feet per minute. The velocity with which the air strikes a lamp
carried against it is increased by the amount equal to the rate at
which the fireboss travels. If he walks at the rate of, say, 4 miles an
hour or 352 feet a minute (on the gangways he will usually have to move
faster than this to make his rounds on time) he will create by his own
motion (and in still air) a velocity practically the same as that at
which the unbonneted Davy is considered unsafe.
[Illustration: Open oil lamp commonly worn on hat. Wick is inverted in
spout.]
[Illustration: Acetylene or carbide lamp for cap or hand.]
History of the Safety Lamp.
The safety lamp, the miner’s faithful and indispensable companion at
his dangerous work, has been, heretofore, considered as the invention
of the famous English scientist, Humphrey Davy, though the name of
George Stephenson, of locomotive fame, has also been mentioned in
this connection. Both came out with their inventions about the same
time, but neither of them is the real inventor of the safety lamp; for
there was, as proven by Wilhelm Nieman, a safety lamp in existence two
years before Davy’s invention became known. It was not inferior to the
latter, but rather surpassed it in illuminating power. Previous to
this, all the precaution employed for the prevention of the threatening
dangers of firedamp had been quite incomplete. One tried to thoroughly
ventilate the mines by fastening a burning torch to a large pole, which
was pushed ahead and exploded the gases. This was extremely dangerous
work which, in the Middle Ages, was generally done by a criminal,
in order that he might atone for his crimes, or by a penitent for
the benefit of mankind. The attempt to substitute for the open light
phosphorescent substances, encased in glass, was not much of a success.
An improvement was the so-called steel mill, invented about 1750 by
Carlyle Spedding, manager of a mine. This steel mill consisted of a
steel wheel which was put into rapid motion by means of a crank. By
pressing a firestone against the fast revolving wheel, an incessant
shower of sparks was produced giving a fairly good and absolutely safe
illumination. However, the running expenses of his apparatus, which
necessitated the continual services of one man, were very high; for
instance, the expenditure for light in a coal mine near Newcastle in
the year 1816 amounted to about $200 per week. Nevertheless, the steel
mill was very much appreciated and in use for a long time, only to be
slowly supplanted by the safety lamp.
[Illustration: ELECTRIC CAP LAMP AND BATTERY.
The safety lamp when left too long in air containing much explosive gas
may cause an explosion, and it is extinguished by certain unbreathable
gases. The electric lamp burns safely regardless of the atmosphere,
but gives no warning of poisonous or explosive gases. It is often used
by rescue men wearing oxygen helmets to enter mines full of poisonous
gases after explosions.]
~THE MAN WHO INVENTED THE SAFETY LAMP~
At the beginning of the nineteenth century the existing coal mines
were worked to the limit and the catastrophies, caused by firedamp,
increased in an alarming manner. In fact the distress was so great that
in 1812 a society for the prevention of mine disasters was formed at
Sutherland, and the origin of the safety lamp can be traced back to
the efforts and labors of this organization. Dr. William Reid Clanny,
a retired ship’s surgeon, was probably the first to undertake the task
(in the year 1808), which he successfully finished with energy and
skill. He concentrated his efforts at first on the separation of the
flames from the surrounding atmosphere, but he did not succeed till the
latter part of 1812, when he constructed a lamp that seemed to meet
all requirements. The report of this invention was submitted to the
Royal Society of London, May 20, 1813, and was printed in the minutes
of that academy. The casing of this original safety lamp was closed
at the top and bottom by two open water tanks; the air was pumped in
by means of bellows and, passing in and out, had to go through both
these reservoirs which acted as valves, so to speak. The lamp proved to
be absolutely safe and was successfully introduced by the management
of Herrington Mill pit mine. The clumsy parts of this apparatus were
eliminated by its inventor by various improvements. The so-called steam
safety lamp was completed in December, 1815, and installed in several
mines. In the meanwhile, two competitors made their appearance. George
Stephenson had finished his lamp October 21, 1815, and Davy published
his first experiments November 9, 1815, in the Transactions of the
Royal Society of London. Clanny’s lamp, nevertheless, stood the test in
the face of this competition, through its much superior illuminating
power, and more particularly as it still continued to burn when the
Davy and Stephenson lamps had gone out. To Clanny, therefore, belongs
the distinction, in the history of invention, of having constructed the
first reliable safety lamp.
What Is a Metal?
The oldest known metals in the world are gold and silver, copper, iron,
tin and lead. They are to-day still the most useful and widely-used
metals. Some of the properties by which we distinguish metals are the
following: They are solid and not transparent; they have luster and
are heavy. Mercury is an exception to the rule; it is a liquid, though
yet a metal, and there is another, sodium, which is solid, though very
light.
What Is the Most 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 for a pound of gold than for a pound of iron.
We mean in useful value--iron is in that sense the most valuable metal
known to man. This is true because iron is of such great service to man
in so many ways, and it is very fortunate that there is such a great
amount of it available for man’s purposes. Iron is not generally found
in a pure state in the mines. It is generally found compounded with
carbon and other substances, and we obtain pure iron by burning these
other substances out of the compound.
Iron is put upon the market in three forms, which differ very much in
their properties. First, there is cast-iron. Iron in this form is hard,
easily fusible and quite brittle, as you will know if you ever broke a
lid on the kitchen range. In the form of cast-iron it cannot be forged
or welded.
Next comes wrought-iron, which is quite soft, can be hammered out flat
or drawn out in the form of a wire and can be welded, but fusible only
at a high temperature. Third comes steel, the most wonderful thing we
produce with iron. It is also malleable, which means that it is capable
of being hammered out flat and can easily be welded, and this is the
great property of steel--it acquires when tempered a very high degree
of hardness, so that a sharp edge can be put on it, and when in that
shape it will easily cut wrought-iron. Ordinarily we make wrought-iron
and steel from iron that has been changed from its original state to
cast-iron.
The term cast-iron is generally given to iron which has been melted and
cast in any form desired for use. Stoves are made in this way. The iron
is melted and then poured into a mold; while the product out of which
wrought-iron and steel are made is technically cast-iron, the term
pig-iron is used in speaking of iron which is cast for this purpose.
The process by which pig-iron is changed into wrought-iron is called
_puddling_. The object of puddling, which is done in what is called a
reverberatory furnace (which is a furnace that reflects or drives back
the flame or heat) is to remove the carbon which is in the pig-iron.
This is done partly by the action of the oxygen of the air at high
temperature and partly by the action of the cinder formed by the
burning furnace. When this has been done the iron is made into balls of
a size convenient for handling. These are “shingled” by squeezing or
hammering and passed between rolls by which the iron is made to assume
any desired form.
Now we come to steel, the most wonderful product or form in which we
take advantage of the value of iron. Steel was formerly made from
wrought-iron, so that you first had to get cast-iron, from which
you made wrought-iron, and eventually got steel by changing the
wrought-iron. Now we make steel direct from pig-iron. This is known as
the Bessemer process.
The most noticeable feature in the chemical composition of the
different grades of iron and steel is found in the percentages of
carbon they contain. Pig-iron contains the most carbon; steel the next
lowest, and wrought-iron the least.
Iron has been known to men from early historical times. The smelting
of iron ores is not any indication of advanced civilization either.
Savage tribes in many parts of the world practiced the art of smelting,
even before they could have learned it from people who had become
civilized.
Why Is Gold Called Precious?
Gold is called one of the precious metals because of its beautiful
color, its luster, and the fact that it does not rust or tarnish when
exposed to the air. It is the most ductile (can be stretched out into
the thinnest wire), and is also the most malleable (can be hammered
out into the thinnest sheet). It can be hammered into leaves so thin
that light will pass through them. Pure gold is so soft that it cannot
be used in that form in making gold coins or in making jewelry. Other
substances, generally copper, are added to it to make the gold coins
and jewelry hard. Sometimes silver is also added to the gold with
copper. The gold coins of the United States are made of nine parts of
gold to one of copper. The coins of France are the same, while the
coins of England are made of eleven parts of gold to one of copper.
The gold used for jewels and watch-cases varies from eight or nine to
eighteen carats fine.
Another reason why gold is called a precious metal is that it is very
difficult to dissolve it. None of the acids alone will dissolve gold,
and only two of them when mixed together will do so. These are nitric
acid and hydrochloric acid. When these two acids are mixed and gold put
into the mixture the gold will disappear.
What Do We Mean By 18-Carat Fine?
We often hear people in speaking of their watches say, “It is an
18-carat case.” Others speak of 14-carat watches or 22-carat or
solid-gold rings.
When you see the marks on a watch-case or the inside of a gold ring
they read 18 K or 14 K, or whatever number of carats the maker wishes
to indicate. A piece of gold jewelry marked 18 K or 18 carats means
that it is three-fourths pure gold. In arranging this basis of marking
things made of gold, absolutely pure gold is called 24 carats. Then if
two, six or ten twenty-fourths of alloy has been added, the amount of
the alloy is deducted from twenty-four, and the result is either 22, 18
or 14 carats fine, and so on. On ordinary articles made by jewelers the
amount of pure gold used is seldom over 18 carats, or three-fourths.
Weddings rings (and these are considered solid gold) are generally made
22 carats fine, that is, there are only two twenty-fourth parts of
alloy in them.
Why Does Silver Tarnish?
Silver is a remarkably white metal, which is associated with gold as
one of the precious metals. It is harder than gold and will not rust,
although it will tarnish, which gold will not, when exposed to certain
kinds of air.
The silver tarnishes when it is exposed to any kind of air that has
sulphur mixed in it. It ranks below gold as a precious metal for use in
making ornaments and is not so costly, because there is a great deal
more of it to be found in the world.
While silver is somewhat harder than gold, it is still not sufficiently
hard to use pure for making coins, so, as in the case of the gold
coins, it is mixed with something else--copper--to harden it. Otherwise
our dimes and quarters would wear out too rapidly. Our silver coins are
made of nine parts of silver to one of copper. The coins of France are
in the same proportion, while the silver coins of England are made of
92¹⁄₂ parts of silver to 7¹⁄₂ parts of copper. German silver coins are
made of three parts of silver and one of copper.
Why Do We Use Copper Telegraph Wires?
One of the characteristics which distinguishes copper is its color--a
peculiar red. It stands next to gold and silver in ductility and
malleability, and comes next to iron and steel in tenacity--which
means the ability of its tiny particles to hang on to each other.
That is why copper wire bends instead of breaking when you twist
it. But that is not the only reason, although an important part of
the reason, why we use copper for telegraph wires. Copper is an
extremely good conductor of electricity when it is pure. So are gold
and silver, but we cannot afford to buy gold and silver wires for the
telegraph, telephone and other wires, and if we used such wires the
cost of the equipment would be so great that we could not afford to
have telephones in our homes. But there is a great deal of copper in
the world and it is very cheap, and so it makes an ideal element for
use in things through which electricity is to pass. When you compound
it with other substances it loses some of its conductivity. Copper
is used extensively in many ways in the world. This book is printed,
for instance, from copper electrotype plates. The whole business of
electrotyping is based on the use of copper.
Why Is Lead So Heavy?
Lead is a white metal and is noted for its softness and durability. It
has a luster when freshly cut, but becomes dull quite soon after the
freshly-cut surface is exposed to the air. Lead is the softest metal in
general use. It can be cut with an ordinary knife. It can be rolled out
into thin sheets, but cannot be drawn out into wire.
Lead is a very dense metal, that is, its particles are very compact
and there is no room for air to circulate in between these particles.
A piece of wood is lighter than a piece of lead of exactly equal bulk,
because the little particles which make up the piece of wood are not
very close together, and there is a lot of air in the ordinary piece of
wood, while this is not true of the lead.
A great deal of lead is used in making pipes for plumbing. This is
because lead pipe is comparatively cheap, although you might not think
so when you think of the general conclusions we have been brought to
form about plumbers and everything connected with them. Lead pipe is
easily bent in any direction also, and is particularly good for use in
plumbing for that reason.
Another wide use of lead is in making paints--white lead being the base
used in making oil paints. The process of making white lead for paint
is quite interesting and pictures of it are shown in “The Story In a
Can of Paint” in another part of “The Book of Wonders.”
Why Are Cooking Utensils Made of Tin?
Tin is the least important of the six useful metals. It is also
inferior in many ways to the others in this group of elements, but is
tougher than lead and will make a better wire, though not a really good
one. It has a whiteness and a luster that are not tarnished by ordinary
temperature and is cheap. That is why it is used in making cooking
utensils, pans, etc., and for roofs. But the pans, roofs, etc., are not
pure tin. They are thin sheets of iron coated with tin. Pure tin would
not be strong enough for these purposes, so a sheet of iron is first
taken to supply the strength and then covered with tin to improve the
appearance of the tin pans and keep them from rusting rapidly.
What Is Gravitation?
Gravitation is the result of the attraction which every body, no matter
what its size, has for every other body. It is a strange force and
difficult to explain in plain words. It is what keeps the heavenly
bodies in their paths. Every one of the planets is held in its path
by gravitation and every object on each of the planets is kept on the
planet by gravitation. We can come nearer understanding gravitation by
studying the effect of the attraction of gravitation on our own earth
and the objects on it. When you throw a ball or a stone into the air
it is the attraction of gravitation that causes it to come back. If
this were not so the stone would go on up and up and would keep on
going forever. If it were not for this wonderful force you could jump
into the air and just keep on going up with nothing to bring you back.
The reason you do not pull the earth toward you is because the body or
mass with the greater bulk has always the greater pulling power.
This is a wonderful force. It cannot be produced nor can it be
destroyed or lessened. It just is. It acts between all pairs of
bodies. If other bodies come between any pair of bodies the attraction
of gravity between the two outside bodies is neither lessened or
increased, and yet each of the outside bodies will have an independent
attraction or pull on the body which is in between.
No particle of time is spent by the transmission of the force of
gravity from one body to another, no matter how far apart they may be.
The only effect that distance has on the attraction of gravitation is
to lessen its force. Any body which is being pulled through gravity
toward another body would fall toward the center of the attracting body
if all the force of attraction from all other bodies were removed.
What Is Specific Gravity?
Specific gravity is the ratio of weight of a given bulk of any
substance to that of a standard substance. The substances taken as
the standard for solids and liquids is water, and air or hydrogen for
gases. Since the weights of different bodies are in proportion to their
masses, it follows that the specific gravity of any body is the same
as its density, and we now generally use the term “density” instead of
specific gravity.
To find, for instance, the specific gravity of a given bulk of silver,
we must take an equal bulk of water and weigh it. Then we also weigh
the silver. We find that the silver weighs ten and a half times as much
as the water, and so the specific gravity of silver is 10.5. If you
will bear in mind that water is the standard used for measuring the
specific gravity of solids and liquids, and that air or hydrogen are
used as standards for the gases, you will always know what the figures
after the words specific gravity mean.
Why Do We See Stars When Hit On the Eye?
We do not really see stars, of course, when we are hit on the eye or
when we fall in such a way as to bump the front of our heads. What we
do see, or think we see, is light.
To understand this we must go back to the explanation of the five
senses--sight, hearing, feeling, tasting and touching. Now, each of
these senses has a special set of nerves through which the sensations
received by each of the senses is communicated to the brain and, as
a rule, these special nerves receive no sensations excepting those
which occur in their own particular field of usefulness. The eye then
has nerves of vision; the nose, nerves of smell; the ear, nerves of
hearing; the mouth, nerves of taste, and the entire body nerves of
touch. As we have seen then, these special nerves are susceptible of
receiving impressions or sensations only in their particular field.
But, if you should be able to rouse the nerves of smell in an entirely
artificial way and give them a sensation, they might easily act very
much as though they smelled something. We find this often in the nerves
of touch when we think we feel something when we do not.
Now, when some one hits you in the eye, the nerves of vision are
disturbed in such a way as to produce upon the brain the sensation of
seeing light. In other words, you cannot affect the eye nerves without
causing the sensation of light, and that is just what happens when some
one hits you in the eye.
[Illustration: “ARGONAUT, JUNIOR.”