THE STORY OF COAL
By CHARLES FITZHUGH TALMAN
Editorial Writer for the Scientific American
MENTOR GRAVURES
FOSSIL FERN FROM COAL MINE · TIPPLE AT BITUMINOUS COAL MINE · COAL CAR DUMPER IN OPERATION · CHARGING COAL IN A MODERN GAS PLANT · SMOKE PROBLEM, SCENE IN PITTSBURGH BEFORE AND AFTER SMOKE CURE · RESCUE PARTY ENTERING MINE AFTER EXPLOSION
Entered as second-class matter March 10, 1913, at the postoffice at New York, N. Y., under the act of March 3, 1879. Copyright, 1913, by The Mentor Association, Inc.
Were it possible for the lump of coal that we burn in our stove, grate or furnace to tell its story, it would take us back millions of years to a time when vast areas of the earth’s surface were covered with swamps, supporting a luxuriant vegetation. No human being, mammal or bird yet existed. Animal life included fish, shellfish and other aquatic species, besides reptiles and insects. The vegetal forms resembled our modern ferns, horsetails, club-mosses and evergreens. The atmosphere was heavily charged with moisture, and a mild climate prevailed even in the polar regions. Such were the conditions under which, during the great Carboniferous Age, most of the existing coal-beds were deposited in the earth.
FOREST SWAMP OF THE CARBONIFEROUS PERIOD (Coal Age). From a drawing by Potonié and Gothan
Coal is the litter of primeval swamps and forests. Year after year the débris of the humid jungles accumulated in shallow water or in the boggy soil, where it underwent partial decay, and was thus converted, first of all, into the slimy or spongy material known as “peat.” Similar deposits are in process of formation in the swamps of the present day, and the peat obtained from them is dried and used as fuel on an extensive scale in some parts of the world; especially Ireland, Holland, Germany and Scandinavia.
CONCRETE PORTAL OF A “DRIFT” MINE
Gradual changes in the elevation of the land led to the submergence of the prehistoric peat bogs, during successive intervals of time, by lakes or shallow seas. Thus their vegetation was killed, and they were overspread with layers of mud or sand, above which, during a subsequent period of elevation, a new peat bog would form; and this process was repeated several times. The conversion of the peat into coal appears to have resulted from the pressure of the overlying strata, probably aided by the internal heat of the earth. Much of its moisture was squeezed and evaporated out; the proportions of its component gases were reduced; and the result was a hard mineral, which has earned the popular name of “black diamond” because consisting chiefly of carbon—the same chemical element which, in a pure and crystalline form, constitutes the true diamond. Chemically, coal consists of carbon; the gases hydrogen, nitrogen and oxygen; sulphur; and ash (the mineral matter that remains after combustion).
Courtesy of United States National Museum
Comparative coal supplies of the world. The nick in the smallest cube shows how much hard coal has been used up. Soft coal cube has hardly been scratched
The record of these long-ago events is found when we sink a shaft through typical coal-bearing strata. We pass through not one, but several, layers of coal, which may vary in thickness from a fraction of an inch to a hundred feet or more, and are separated by generally much thicker layers of sandstone or shale (solidified clay). The layers of coal are known as “coal-beds.” Unless a coal-bed is at least two feet thick it is hardly worth working, and, ordinarily, the thickness of a bed does not exceed eight or ten feet. The shale or sandstone above a bed is very commonly found to contain the remains or the impressions of the ancient plants from which the coal was formed. A study of these remains and casts has made it possible to classify hundreds of species of plants now extinct. Fragments of plants are also sometimes found in the coal itself, and thin slices of coal frequently show a vegetable structure under the microscope. Finally, to furnish conclusive proof of the vegetable origin of coal, we find under the coal-bed a layer known as the “underclay,” which is a fossil soil filled with the roots and rootlets of the coal-producing plants. Different conditions of formation, and also, probably, differences in the character of the original vegetation, have resulted in the production of different kinds of coal. The most important heat-producing constituent in coal is the elementary substance called “carbon,” and the simplest classification of solid fuels depends upon the percentages of fixed (non-volatile) carbon they contain, the average percentages running as follows: Wood, 50%; peat, 55%; lignite, 73%; bituminous coal, 84%; anthracite coal, 93%. When fuel is burned the greater part of it unites chemically with the oxygen of the air to form certain invisible gases—especially carbon dioxide and water-vapor—and only the ash remains.
From “Geology, Physical and Historical,” by H. P. Cleland. American Book Co., N. Y.
Section of coal-bearing strata in Pennsylvania, showing relative amount of coal and barren rock in a rich field
In the popular mind coal is classified as hard or soft, while hard coal is further classified according to the size of the lumps. For both scientific and industrial purposes more elaborate classifications are necessary, and several have been used or proposed.
COAL FIELDS OF THE UNITED STATES
Kinds of Coal
The United States Geological Survey classifies coals, first of all, according to “rank,” depending upon both chemical and physical characteristics. Anthracite, which contains the largest percentage of carbon, ranks highest, and lignite, with the smallest percentage of carbon, lowest. Coals of the same rank are said to be of high or low “grade,” according to whether they contain a relatively small or large percentage, respectively, of ash and sulphur. The ranks recognized by the Survey are: Anthracite, semi-anthracite, semi-bituminous, bituminous, sub-bituminous, and lignite.
Courtesy of U. S. Bureau of Mines
AN “ENTRY” IN A COAL MINE
Showing timbered roof
Courtesy of U. S. Bureau of Mines
COATING WALLS OF A MINE WITH CEMENT
To prevent coal-dust explosions
DRILLING IN COAL FOR BLASTING
“Anthracite” is the hardest of coals. It was formed from bituminous coal under the crushing pressure due to the upheaval of mountains or by the intense heat of adjacent molten rocks. Most American anthracite is mined in eastern Pennsylvania. The largest deposits in the world are found in China. Anthracite burns slowly, with little smoke. It is well adapted for domestic use on account of its cleanness, but is not an economical fuel for steam-raising or general manufacturing.
Press Illustrating Service
MODERN ELECTRIC LOCOMOTIVE
Used for hauling coal from the mines
“Semi-anthracite” also ranks as a hard coal, though it is less hard than anthracite. Very little is mined in this country, and it is generally sold as anthracite.
“Semi-bituminous” coal is a softer coal, which, when properly burned, gives off but little smoke. The best semi-bituminous coal ranks highest among the coals in heating value. It is the most valuable fuel for manufacturing purposes; also for steamships, as it requires less bunker space per unit of heat than any other coal.
“Bituminous” coal, or ordinary “soft coal,” burns readily, with a smoky flame, and is the coal most commonly used for manufacturing purposes; in fact, the bulk of the coal mined throughout the world belongs to this rank. It includes a good many varieties, some of which are extensively used in making coke, while others, such as “cannel” coal, have been in great demand for use in gas-works. Nowadays, however, the widespread introduction of “water-gas,”[2] which does not require any particular kind of coal, has diminished the demand for “gas coals.”
[2] Made by forcing steam over glowing coal or coke. See Monograph No. 4.
“Sub-bituminous” coal, or “black lignite,” is common in some of our western coal fields. It is a clean and useful domestic fuel when used near the mines, but is not very satisfactory for shipment, as it shrinks and crumbles under the effects of “weathering” and is liable to spontaneous combustion.
“Lignite” is the least valuable of coals, and is the form of coal which is the least altered from the original peat. The Geological Survey applies this name only to those coals which are distinctly brown and either markedly woody or claylike in appearance. Lignite, as it comes from the mine, contains from thirty to forty per cent. of moisture, and it “slacks” or falls to pieces much more rapidly than sub-bituminous coal when exposed to the air. It is hardly suitable for transportation.
For commercial purposes coal is also classified according to size. The coal as it comes out of the mine, without any sorting into sizes, is known as “run of mine,” and the semi-bituminous coals are commonly shipped in this form. Most coals, however, are passed over bars or gratings, which constitute screens of different degrees of fineness; each screen permits all the lumps below a certain size to fall through, and thus the coal is divided into the different standard sizes. The sizes of anthracite, from the smallest to the largest, are: rice, buckwheat, pea, chestnut (or nut), stove, egg, broken (or grate), steamboat, and lump. Bituminous coal is divided into slack, nut and lump (the largest size). A mixture of lump and nut is called three-quarter coal.
The Modern History of Coal
Press Illustrating Service
MODERN MINING MACHINE
for undercutting coal. The “cutter bar” is shown in front, filled with “cutting teeth” set in a chain that travels around. See illustration opposite
Press Illustrating Service
SHAKER SCREENS IN A TIPPLE HOUSE
The coal passing over screens is graded according to size
“CUTTER BAR” AT WORK
The bar, with its cutting chain of teeth, makes a horizontal cut deep into the bottom of the seam of coal. Blasting then does the rest
The age of the steam-engine is also the age in which the use of coal has become widespread, and the output of coal is a faithful index of industrial progress. Although the Greek writer Theophrastus (about 300 B. C.) mentions the use of coal as a fuel, and its use was also known to the ancient Britons and the Chinese, it was virtually unknown throughout the Middle Ages. The first record of coal mining in England is of the year 1180 A. D., and coal was first shipped to London in the year 1240. It was long known as stone-coal, pit-coal, etc., to distinguish it from charcoal; also as sea-coal, on account of being carried to London by sea. Bituminous coal was first mined in America in 1750, near Richmond, Virginia. Anthracite was discovered in Rhode Island in 1760, and in Pennsylvania in 1766, but for many years its value was not recognized. As late as the year 1812 Colonel George Shoemaker, of Pottsville, was treated as an impostor and threatened with arrest for attempting to sell a few wagon-loads of anthracite in Philadelphia; methods of burning it were not understood, and it was declared to be merely “black stone.” In the year 1820 only 365 tons of anthracite were sold in this country, as compared with the present annual output of about 90,000,000 tons.
Before the days of the railway coal was shipped mostly by water in rough boats called “arks,” which floated down the rivers to the seaboard towns. As it was impossible to return against the current, the ark was sold with the coal at its destination. A great many arks were wrecked in transit, and the whole process of transportation was a costly one. Only with the introduction of steamboats, canals and railways, did the coal industry assume serious proportions.
The production of coal in America has grown at an amazing rate. In the year 1868 Great Britain produced 3.6 times as much coal as the United States, and the output was also exceeded by that of Germany. In 1899, the United States took the lead. At the present time, with an estimated production for the year 1917 of 643,600,000 tons, the United States is producing nearly half of all the coal mined in the world. Great Britain ranks second, closely followed by Germany.
How Coal is Mined
A relatively small amount of coal is quarried near the surface of the ground from open pits. The overlying soil is removed by steam-shovels, and the coal is then blasted out and shoveled into cars.
Most coal is mined underground. Access to the coal-beds is obtained either by sinking a vertical “shaft” or by driving a tunnel, according to the location of the beds. A tunnel driven at a steep angle is called a “slope.” A horizontal tunnel leading into a coal-seam is called a “drift.” In this country few coal mines are more than 300 or 400 feet below the surface, and the deepest is about 1,600 feet. Much deeper mines are found in Europe, especially in Belgium.
Press Illustrating Service
ROTARY DUMP IN A TIPPLE
Showing a coal car half turned over in order to dump contents
Courtesy of “Coal Age”
SPIRALIZING MACHINES
which, by rotating motion, separate the coal from slate
Courtesy of U. S. Bureau of Mines
MODERN HEADFRAME, BINS AND TRESTLE
Of fireproof construction. Anthracite coal mine
American mine shafts are generally rectangular and are divided into two or more compartments. Where a shaft passes through water-bearing strata it must be provided with a tight lining, or “tubbing,” to prevent the mine from being flooded. All water that enters the mine collects in an excavation, or “sump,” at the bottom of the shaft, and must be pumped to the surface.
The method of working coal-seams most commonly practiced in this country is known as the “room-and-pillar” system. One or more tunnels, or “entries,” are first driven from the bottom of the shaft or the mouth of the drift. These are the main thoroughfares of the mine, and are usually provided with tracks, over which the mine cars are hauled by mules or by some other method of traction—locomotives, endless chains, etc. Secondary entries (“headings,” “butt entries,” etc.) branch off from the main entries. Finally, the work of extracting the coal consists of excavating open spaces, or “rooms,” adjoining the entries.
Courtesy of “Coal Age”
MODEL COAL BREAKER
Note the neat and careful “upkeep” of the place
The actual mining is done in the rooms, and different methods are in use. Anthracite is generally “shot from the solid”; that is, blasted out from the face of the coal without any preliminary cutting. This method is objectionable, especially in bituminous mines (where it is, however, much practiced), because the large charges of powder it requires produce a great deal of coal-dust and weaken the roof and pillars, often leading to falls of coal and fatal accidents. A better plan consists of “undercutting” the coal before it is blasted out. A long groove is made at the level of the floor, either with a pick or with a coal-cutting machine. Holes are then drilled some distance above the groove for the insertion of the blasting charges, and the coal is blasted down. A single shot will sometimes dislodge a ton or two of coal.
The next step is to shovel the coal from the floor into a mine car, which is then pushed into the adjacent entry. The miner attaches a numbered tag to the car, so that he will be duly credited for his work, which is paid for by the ton. The loaded cars are eventually hoisted or hauled out of the mine, to be weighed and discharged above ground.
The final step in working a coal-seam by the room-and-pillar method is to mine out the thick walls or pillars of coal, which are originally left between adjacent rooms to support the roof. As this work proceeds the worked-out sections are filled with waste rock, or the roof is allowed to fall. The object is to leave as little coal in the mine as possible, but practically it is rare that more than 60 or 70 per cent. is recovered.
One feature of a coal mine that must be carefully planned is the system of ventilation. This is provided not merely for the comfort of the miners, but to prevent, as far as possible, the accumulation of poisonous and explosive gases. There are always at least two airways leading into the mine (one or both of which may also be used for hoisting or other purposes), known as the “upcast” and the “downcast,” according to the direction in which the air passes through them. A current of air is maintained either by keeping a fire burning at the bottom of the upcast or by the use of powerful fans or blowers. A system of tight trap-doors prevents the air from taking a short cut between the downcast and the upcast, and thus leaving the greater part of the mine unventilated.
Courtesy of “Coal Age”
MINING FROM THE OUTSIDE
Stripping the surface of a coal-bed with steam shovel, at Pittsburg, Kans.
Courtesy of U. S. Bureau of Mines
WATCHING THE CANARY
for indications of poisonous coal gas. Reserves testing the air of a mine after an explosion
Courtesy of U. S. Bureau of Mines
MEMBERS OF RESCUE TEAM
Showing apparatus worn on entering mines after explosions. This device sustains a man for two hours
The coal in the mine constantly gives off various gases, one of which, the notorious “fire-damp” (methane or marsh-gas), is responsible for many explosions. In recent years it has been discovered that coal-dust itself, when mixed with the right proportion of air, is violently explosive. Mine explosions may be minimized by requiring the use of “safety-lamps” (oil, gasoline, or electric); by providing devices to prevent sparking in electrical apparatus; and by using for blasting operations only so-called “permissible” explosives, which give a shorter and cooler flame than black powder. Coal-dust explosions can be largely prevented by wetting the walls of the mine, or by the new process of “rock-dusting,” which consists of applying dry incombustible powdered rock to all surfaces. Unfortunately, none of these precautions are employed as generally as they should be.
Press Illustrating Service
SAFETY DEVICE IN COAL BUNKER
In case of a “coal slide,” a man may be pulled out before he is buried and stifled
The elevator used for hoisting in the mine shaft is called a “cage.” After the mine cars reach the surface they pass upon an elevated structure called the “tipple.” This is generally the most conspicuous feature of a mining property above ground, and provides facilities for screening and otherwise “preparing” the coal as it passes down chutes to the railway cars underneath. The more elaborate structure used for anthracite is called a “breaker”; it includes machinery for crushing the coal and arrangements for removing “slate” and other waste rock by hand picking or otherwise.
Coal mining in this country gives employment to an army of 765,000 men. The word “army” has a sinister appropriateness in this connection, since out of every thousand men employed in the industry three are killed and one hundred and eighty injured annually.
The World’s Coal Resources
In order of output, the leading coal-producing countries of the world are: United States, Great Britain, Germany, Austria-Hungary, France, Russia, Belgium, Japan, China, India, and Canada. The total production during the latest year for which data are available was about 1,346,000,000 tons.
How long will the world’s coal supply last? This is a question to which various answers have been given. Geologists are able to furnish a rough estimate of the amount of coal now in the ground and near enough to the surface to be mined; but with the growth of the world’s industries the demand for coal is increasing by leaps and bounds, and nobody can safely predict how much will be needed at any future time.
The world’s “coal reserves”—that is, the amount of coal remaining unmined—are estimated at 8,154,322,500,000 tons. In the United States it is estimated that we have used only four-tenths of one per cent. of our available coal supply. At the present rate of consumption the coal in this country would last about 4,000 years; but if the present rate of increase in consumption should be maintained, it would last only 100 years!
Fortunately for posterity there are sources of heat, light and power which are not, like the fuels, exhaustible. Water-power, for example, is a permanent asset, and there are other inexhaustible sources of energy, such as solar heat and the internal heat of the earth, which Man’s ingenuity will someday turn to good account.
Courtesy of “Coal Age”
CARS FOR CARRYING EXPLOSIVES INTO MINES
SUPPLEMENTARY READING
| COAL CATECHISM | By W. J. Nicholls |
| THE STORY OF AMERICAN COALS | By W. J. Nicholls |
| A YEAR IN A COAL MINE | By Joseph Husband |
| YEAR BOOK OF THE U. S. BUREAU OF MINES | |
| STORY OF A PIECE OF COAL | By E. A. Martin |
| THE COAL FIELDS OF THE UNITED STATES (U. S. Geological Survey, Professional Paper 100) | By M. R. Campbell |
⁂ Information concerning these books may be had on application to the Editor of The Mentor.
THE OPEN LETTER
Coal is “a burning question,” that has to be met and answered every day. It supplies heat, light and power—and a thousand and one useful by-products—and it is an ever-present, ever-fruitful subject of public and private discussion. We average folk know something of the varied uses of coal in the big affairs of the world, but we know it more intimately and vitally in the forms in which it ministers to our own personal welfare. Coal, in our everyday—and night—life, means heat and light. It means home comfort—and if this “coal comfort” is denied us, or even curtailed, we raise an immediate and mighty outcry. And why not? The health of a community can be fatally affected by a few heatless days. The experience of the past winter has shown us how dependent we are on fuel, not only for luxury and comfort, but for life itself.
Why do we need so much heat? Many of the peoples of the earth get along comfortably with much less heat than we consider necessary. Europeans and South Americans call us a “steam-heated nation.” Why do we have to surrender so completely and abjectly to the domination of Old King Coal? It is true, as Owen Meredith said: “Civilized man cannot live without cooks”; and light is all important in turning night hours to advantage; but why must we be so warm? Humanity was not created in a warm room, nor was the human race nurtured, in its infancy, by a coal fire or a gas stove. Primitive man was his own heater. He had to discover fire, and then exploit its uses. He was originally supplied by nature with a warm body, and he now finds artificial ways of making it warmer. Has not civilization pampered us to a point that has impaired our original heat-giving resources and substituted a forced warmth that has enervated us? The doctors tell us that many diseases come out of artificial heat—indoor diseases, they might be called—the diseases that are treated, and sometimes cured today, by foregoing artificial heat and going back to nature.
Does this mean that I suggest reverting to primitive conditions and giving up heat? No, indeed. I suffered enough last winter. I do not advocate giving up heat—suddenly. But letting up gradually on artificial heat, I do most earnestly advocate. Most of us live an over-heated existence—to the depletion of our health. The steam pipe, like a huge python, is closing its coils about us, and gradually stifling our native vital resources.
On the coldest days of winter a white-haired man, nearly seventy years of age, may be seen walking New York streets, without a hat, clad only in light “Palm Beach” trousers, and a silk negligée shirt, open at the throat. “He is crazy,” you say. “Perhaps,” I answer, “but at any rate he is healthy—and immune from cold.” Heatless days mean nothing to him. On a raw, drizzling day in November last a slender man was playing golf in a light woolen suit. A companion player, weighing over 200 pounds, full blooded and hearty in appearance, and bundled up in two heavy sweaters, asked the lightly clad player if he was not afraid of catching a fatal cold. “No,” he answered, “you are the one that gives me concern. If I had your clothing on I would be a sick man. I am not healthy enough to wear all those things.”
Which means that we would be better off in health if we could accustom ourselves to less heat; if we could live as the people of some other nations do—comfortable and content with heat enough to take the chill off the air, and not demanding that we shall be “kept going” by means of artificial heat outside of our own natural heat-giving apparatus. We make caloric cripples of ourselves by giving crutches to nature in the form of roaring furnaces and hissing steam pipes. Fresh cold air is better for us than hot air—in winter as well as in summer. Would it not be worth while to form a national Fresh Air Fraternity, based on the principle of foregoing artificial heat and developing the original body caloric? We would then leave artificial heat largely to infants, weaklings and invalids; we would abolish several diseases altogether, improve the mortality rate, and be healthy, happy and vigorous. Incidentally, too, we would have more coal for cooking and other really necessary purposes.
W. D. Moffat
Editor