An interesting story is told in an English book by Edward Cressy, of the great coal strike in 1912. Many factories and workshops had to close for want of fuel. A workman from one of these, on reaching home, purchased a sack of coal and set it up against the back door. Then he sat in the kitchen, in which there was no fire. From time to time, when he felt chilly he got up, flung the sack of coal across his shoulders and ran around the yard until he became warm. That was his way of saving fuel. He was only doing in his own fashion what all engineers and manufacturers are trying to do in other ways all the year round.

The extent to which all manufacture and transport, all industry there, was paralyzed during the strike, shows the complete dependence of modern life upon fuel. In spite of the fact that in Great Britain nearly 240,000,000 tons of coal are raised annually, a temporary stoppage of supply threw all the ordinary machinery of existence out of action and revealed the magnitude of the debt that the world owes to those who win precious stores of fuel from the depths of the earth.

Probably no industrial operation excites more widespread interest, when accorded publicity, than the mining of coal, and that because of the dangers which attend it. The annual list of victims buried beneath a falling roof, or mangled by runaway cars, causes little comment, but every now and then the world is startled by an appalling catastrophe in which hundreds of men lose their lives. From the early days when growing industry demanded more coal, inventors have been busy devising all sorts of safety appliances for the miner.

The original safety-lamp, with which practically everyone is familiar, is the parent of scores of others, each claiming to offer some special advantage. All sorts of mechanical devices to prevent overwinding—an accident which would fling the cage with its coal or human freight out of the pit mouth—have been invented, and every section of the work has been made as safe as human ingenuity and human skill have been able to make it. But the number of disastrous explosions has not been materially reduced.

Many varieties of coal give off a gas known as marsh-gas or fire-damp. This is inflammable and, when mixed with air, violently explosive. It is the presence of this gas that necessitates the safety-lamp. There are a few kinds of mines which evolve no gas, and in these naked lights are used. But all mines must be ventilated by forcing air through them with a fan, and this air must be in sufficient quantity to keep the percentage of gas below a dangerous standard. Most mines are examined at regular intervals by a “fireman” who can estimate approximately the percentage of gas present by the size of the faintly luminous “cap” which hovers above the flame of his lamp.

Explosions have occurred, however, in cases where it is extremely doubtful whether gas has been present in dangerous quantity, and attention has been drawn to the possible causes. Many varieties of coal produce a quantity of fine dust which settles in the roadways, on roof, and sides, and floor. For many years there has been a controversy as to the relative importance of gas and dust in producing explosions, and the question is still one which gives rise to a lively difference of opinion. But there is no doubt that a mixture of coal-dust and air is explosive, and that even if an explosion is started by gas the disturbance creates clouds of dust which gives rise to secondary explosions and spread the disaster over a wider field than was originally affected.

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Consequently a plan has been evolved for the ventilating current to be reversed periodically, in order to remove dust which has settled on the side of timbering and crevices, and the roadways to be watered in order to allay the dust. A plan has also been tried of spreading fine stone-dust in the roadways. This mixes with the coal-dust and renders it less inflammable.

Unfortunately the disastrous effects of an explosion do not end with the explosion itself. The main products of combustion, whether of fire-damp or coal-dust, are carbon monoxide and carbon dioxide. The latter causes suffocation and the former is a dangerous poison. It is the dreaded “after-damp” of the miner. Those who survive an explosion are therefore in danger of suffocation or poisoning, and it becomes imperative to restore the circulation of the air with the least possible delay. For even if the fan has escaped injury, fallen portions of the roof may have choked up some of the roadways, or the explosion may have torn down doorways and provided a short cut for the air. But if the atmosphere is dangerous for men in the pit at the time, it is equally dangerous for others to go down and effect repairs or render first aid.

The work of the rescue party is therefore a labor of desperate heroism and often attended by additional loss of life. It has recently been found possible to reduce the dangers of after-damp by providing rescue parties with respirators fitting over the mouth and nose, and supplied with oxygen from two steel bottles of the compressed gas strapped across the back. An effective apparatus of this kind, such as has been adopted by the United States Government for the use of the Bureau of Mines Rescue Crew, is shown in the accompanying illustration. The bag in front is known as a “breathing bag” and has separate compartments for the inhaling and exhaling, the tube at the right leading to the former and that at the left to the exhaling compartment, which usually contains sticks of caustic soda to absorb the carbon dioxide exhaled by the wearer.

Coal is largely formed from vast masses of vegetable matter deposited through the luxuriant growth of plants in former epochs of the earth’s history. In the varieties of coal in common use the combined effects of pressure, heat and chemical action upon the substance have left few traces of its vegetable origin; but in the sandstones, clays and shales accompanying the coal the plants to which it principally owes its origin are presented in a fossil state in great profusion and frequently with their structure so distinctly retained, although replaced by mineral substances, as to enable the microscopist to determine their botanical affinities with existing species. Trees of considerable magnitude have also been brought to light.

The animal remains found in the coal-measures indicate that some of the rocks have been deposited in fresh water, probably in lakes, while others are obviously of estuarine origin, or have been deposited at the mouths of rivers alternately occupied by fresh and salt water. The great system of strata in which coal is chiefly found is known as the carboniferous.

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There are many varieties of coal, varying considerably in their composition, as anthracite, nearly pure carbon, and burning with little flame, much used for furnaces and malt kilns; bituminous, a softer and more free-burning variety; and cannel or “gas-coal,” which burns readily like a candle, and is much used in gasmaking. The terms semi-anthracite, semi-bituminous, coking coal, splint coal, etc., are also applied according to peculiarities.

All varieties agree in containing from 60 to over 90 per cent of carbon, the other elements being chiefly oxygen and hydrogen, and frequently a small portion of nitrogen. Lignite or brown coal may contain only 50 per cent of carbon. For manufacturing purposes coals are generally considered to consist of two parts, the volatile or bituminous portion, which yields the gas used for lighting, and the substance, comparatively fixed, usually known as coke, which is obtained by heating the coals in ovens or other close arrangements.

About 260,000,000 tons of coal are annually mined in Britain, the value being over $300,000,000. Large quantities are exported. The British coal-fields, though comparatively extensive (covering about 9,000 square miles), are far surpassed by those of several other countries, as the United States and China, the former having coal-fields estimated to cover about 451,000 square miles; the latter over 200,000 square miles. Britain no longer mines the largest quantity, having been far surpassed by the United States. Other countries in which coal is worked are Belgium, France, Germany, Russia, India, New South Wales and Canada. China has hitherto mined only on a small scale.

The annual production of anthracite coal in Pennsylvania is more than 86,000,000 tons of 2,240 pounds, valued at the mines at $198,000,000. In 1910 there were produced of bituminous coal 388,222,868 tons, valued at $463,654,776; amount of coke manufactured, 37,000,000 tons. This was distributed widely over the country, the greatest producers, after Pennsylvania, being Illinois, West Virginia, Ohio, Alabama and Colorado.

Recently a very large output of coal has been discovered in Alaska, the value of which is as yet undetermined, though it is believed to hold a vast quantity of coal. The value of the western coal-fields also is far from known, and since 1906 very extensive tracts of coal-bearing lands have been withdrawn from settlement, principally in Wyoming, Montana, Colorado, Utah and New Mexico, their beds being largely of lignite. These cover about 50,000,000 acres, and, with those of Alaska, are held by the government as national assets. The mines of Alaska are claimed to be exceedingly rich, both in bituminous and anthracite coal, the beds examined being estimated to contain 15,000,000,000 tons, while there are large districts unexamined. They have not yet been worked, the government keeping them back for public ownership.

How can We Hear through the Walls of a Room?

We are able to hear easily through the walls of many rooms because the material used in those walls are good conductors of sound. We know that some things are better conductors of heat than others, and just in that same way, some things conduct sound better than others. Wood has been shown to be an even better conductor of sound than air. Most of us have stood at the foot of an overhead trolley pole to see if we could hear a car coming, and we know that the reason we did this was because we could hear the wire humming, when we put our ears against the pole, even though we could not hear any sound in the air.

When we are in a room that has wooden walls we can hear sounds in the next room very plainly, not because the wall is thin, but because the wood in the wall is a good conductor of sound. Other walls made of different kinds of material, are not as good conductors of sound. While you may hear through them, you cannot hear as plainly as you can through a wooden wall.

What is a Diesel Engine Like?

The Diesel engine has caused a great deal of comment of late years because of the spectacular uses to which it has been successfully applied. A specially constructed Diesel engine was probably the chief aid in the accomplishment of the first submarine trans-Atlantic voyage by the German submarine “Deutschland.”

It is an oil engine which was invented by Rudolph Diesel in 1893.

The engine operates at compression pressures very much higher than those used in any other internal combustion engines, and it dispenses with the usual igniting devices by rendering the air charge incandescent by compression.

The efficiency of the Diesel engine is high, and it can use low grades of fuel, but it has the disadvantage of greater weight per horse-power than other engines.

It has found increasing favor for use in marine propulsion, and in 1913 was adapted to high-speed railway service, and put into use in Germany.

What does the Sheep-Grower Get for the Wool in a Suit of Clothes?

A man’s ordinary three-piece fall suit has about nine pounds of wool in it. Such a suit might cost somewhere between twenty and forty dollars, depending on whether it was bought ready made or whether it was made to order. If the price was questioned, the retailer would probably explain that it was all wool and that the wool cost was the reason it was expensive, and still the sheep-man who raised the wool only received an average of about eighteen cents a pound, or $1.62, for all the wool used on the suit.

Of course, the largest part of the cost of a suit of clothes is really accounted for by the cost of transportation, weaving, tailoring and selling, but we must all agree that the sheep-man who tends the flock all winter and cuts the wool in the spring is not to blame for high prices.