COAL

COAL is so much "a matter of course" in our daily life that most people are only now, when its supply is becoming precarious, anxious to know something of its nature and history. By the word "coal," or "coles," our ancestors understood what we now distinguish as "charcoal," prepared from wood by the "charcoal-burner," or "charbonnier," as the French call him. What we now call "coal" was known to them as "sea-coal," and, later, as "black" or "stone cole," to distinguish it from "brown coal," known nowadays as "lignite," though the name "stone coal" is locally applied in England to that very hard kind of black coal also called "anthracite," of which jet is only an extremely hard and dense variety found in small quantities in the oolitic strata of Whitby, Spain, and other localities.

It is on record that in the year 1306 a citizen of London was tried, condemned, and executed for burning "sea-coal." This severe treatment was held to be justified by the poisonous and otherwise injurious nature of the smoke produced by fires of sea-coal. I have not met with any records of the earliest digging for and trade in "sea-coal," but presumably it was obtained near the coast in the North of England and brought to London by ship—hence its name. The coal-trade of Newcastle began in the thirteenth century, but, owing to an Act of Parliament in the reign of Edward I forbidding the use of sea-coal in London, did not become important until the seventeenth century. It came very gradually into use, and we find that Evelyn (the diarist) in 1661 noted the withering and bad condition of rose-bushes and other plants in London gardens, which he attributed to the pestilential action of the smoke given off by the newly introduced "sea-coal" which was increasingly used as fuel in London houses. The sea-coal was not yet largely, if at all, used in the production of iron; and Evelyn as a forest-owner and lover of trees, has much to say about the necessity for attention to the cultivation of our forests in connection with the iron industry which then flourished in the Weald of Sussex; charcoal procured by the slow burning or roasting of wood being the fuel used in the smelting furnaces, whilst the ore was the orange-brown wealden sand. It was during the eighteenth century that what we now call simply "coal" came rapidly into use—not only for domestic heating, but for furnaces of all kinds employed in industrial enterprise, and, at a later date, for the earlier and later forms of steam-engines. The smoke of the new coal was everywhere regarded as a terrible nuisance, and a source of injury to both animal and vegetable life. The poisonous action of coal-smoke is not due to the finely divided black particles of carbon of which it largely consists, but to the sulphuric acid derived from the small quantities of sulphur present in coal. It is calculated that more than sixteen million tons of coal are annually used in London alone for heating purposes, and that 480,000 tons of black carbon powder are discharged over London by its chimneys every year, together with very nearly the same weight of poisonous sulphuric acid!

What, then, is this "sea-coal" or "coal" of our modern life? We all know its black, glistening appearance, and more or less friable character. Its nature and origin are best conveyed by the statement that it is very ancient "peat," compressed and naturally changed by chemical action and retaining little or no trace of its original structure. Peat, as we know it from the low land of English and French river valleys and the bogs of Scotland and Ireland, is formed by the annual growth and death of "mosses" of several kinds and of other accompanying vegetation. It retains the woody forms of the vegetable growths which constitute it, and they are often but loosely adherent to one another. Peat may be merely a growth of the past five years, but is sometimes many thousand years old. Older than peat, and more caked and compressed, is lignite, or brown coal, which occurs on the Continent of Europe, also in South Devon and elsewhere, in geological strata newer than those which yield our black coal. Then we have the most important class of black coals which are known as "bituminous coals," because they soften when heated and form hydrocarbons of both viscid and gaseous nature. They are used for domestic purposes, and wherever flame is desired. They are, in fact, the "lumps of coal" familiar in our scuttles. The "bituminous coal" with the greatest amount of hydrogen in it is the cannel or candle coal, so called from its bright flame when burning. This kind is especially valuable for gas-making, and of smaller value as fuel. The term "anthracite" is reserved for a hard, stone-like coal which is very nearly pure carbon (ninety per cent). This class of coal burns with a very small amount of flame, gives intense heat, and no smoke. It is used in drying malt and hops.

Like all woody matter, that from which peat is formed consists of a combination of the elements carbon, hydrogen and oxygen; and these remain in somewhat changed chemical union in the brown coal, bituminous coal, and anthracite. The carbon and a varying and small proportion of the original hydrogen of the woody peat, are the important elements in coal; and we may well ask how they come to be produced as a black or dark brown mass from dead vegetable growths which are often bleached and colourless. It is true that vegetable refuse does not necessarily blacken when left to itself. We know that by roasting or charring wood (or animals' flesh or bone) we can drive off the elements oxygen and hydrogen and nitrogen (if there), and obtain a black mass of carbon (so-called charcoal). That blackness is the actual true tint of carbon. The dead weeds and leaves at the bottom of a stagnant pond break down and form a pitch-black mud. They would not, and do not, go black if exposed to the oxygen of the atmosphere; but at the bottom of a stagnant pond or in a refuse heap they are excluded from the air, and a microbe—a bacterium which has been carefully studied, and is of a kind which can only flourish in the absence of free oxygen—attacks the dead weeds, producing by change of their substance marsh-gas and black carbon, the black mud emitting bubbles of gas which one may stir up with a pole in such a pond. This chemical attack by anaËrobic bacteria goes on in the deeper layers of all marshes and stagnant pools, remote from the oxygen of the air; and it is fairly certain that the black coal which we find in strata of great geological age was so produced by the action of special kinds of bacteria upon peat-like masses of vegetable refuse. Indeed, by studying microscopic sections of coal, numerous forms of bacteria have been recognized which might be capable of effecting such chemical changes. On the other hand, we must remember that it is not possible to conclude by form alone as to what subtle chemical work a bacterium or bacillus or micro-coccus may be, or may have been, carrying on. The peat-like deposits which became carbonized and so formed the "coal" were probably masses of algÆ, mosses and soft aquatic plants, which were brought down and accumulated in swampy, forest-covered ground about the mouths of rivers, the deposit being covered in owing to rapid oscillations of level by beds of sand or clay, followed by new growth and deposit.

Our British coal and a good deal of foreign coal is found in certain stratified rocks of the earth's crust known as "the Carboniferous System," about 12,000 ft. thick, consisting chiefly of very dense limestone. The "seams," or stratified beds of coal, occur in sandy rock known as the "Coal Measures," and vary in thickness from a mere film to 40 ft. Above the Carboniferous System are later deposits, some 14,000 ft. in thickness—the Permian, Triassic, Jurassic, Cretaceous, and Tertiary strata. Below them we find stratified deposits containing fossilized remains of plants and animals, to a depth of another 40,000 ft.: they are the Devonian, Silurian, and Cambrian "systems" or series of strata. Coal of a workable nature is found in many parts of the world in the beds or strata of later age than our Coal Measures—namely, those of Jurassic, Cretaceous, and Tertiary age.

Coal is so valuable and used in such vast quantities by modern man that, though procured at first from beds lying at or near the surface, it has been found remunerative to mine far into the depths of the earth's surface, where its existence is ascertained, in order to procure it. A depth of 4000 ft. is apparently the limit set to such mining by the increase of temperature in mines which penetrate to that extent below the surface. In 1905 the annual output of British coal-mines was in round numbers 230,000,000 tons. It is certain that there is a limit to this production, but not possible to calculate what that limit may be, owing to the uncertainty as to the future working of coal-fields as yet unexplored.

Such questions have been, and are being, considered by experts on behalf of the Government. A matter of interest of another kind is that in and associated with the coal seams of our Coal Measures, fossilized remains of peculiar fern-like trees, ferns, and other strange plants, and of very peculiar, extinct newt-like animals (as large as crocodiles) are found in great variety. The notion that the toads occasionally found embedded in the black mud of a coal-yard or even in a fractured lump of coal are survivals from the time—many millions of years past—when the plants and animals of the Coal Measure swamps were living, is a baseless fancy. The toads so found are of the kind or species now living on the earth—totally different from those whose bones occur in the Coal Measures, and the presence of such modern toads embedded in black slime, in coal-heaps in store-yards, or even in coal-scuttles, is only what may be expected to occur and does occur in damp quarries and other places where these familiar little beasts love to hide.