Coal ash

“ White ash anthracite coal of the grade that between January 1, 1915, and January 1, 1917, was uniformly sold and recognized in the coal trade as coal of White ash grade; Red ash anthracite coal of the grade that between January 1, 1915, and January 1, 1917, was uniformly sold and recognized in the trade as coal of Red ash grade ”

“ The coal which contains twenty per cent. or less of volatile matter is a free-burning coal that may develop heat enough to partly fuse the ash, forming "clinkers"; it is therefore called "caking" coal, and is not only well adapted for use as fuel and steam-making, but it is also a good smelting coal.
Coal which contains more than thirty per cent. of volatile matter is known as "fat" coal and is generally used in the manufacture of coke and illuminating gas. Western Pennsylvania produces the largest amount of fat coal, but [Pg 151] it is found here and there in nearly all soft-coal regions. ”

“ Anthracite, another form of carbon, is used as fuel for strong furnaces. It leaves little “ash,” and is smokeless when burned. Coal, in all its forms, is evidently derived from wood. Thousands of years ago vegetable matter must have been embedded in the ground and subjected to carbonization. There are different kinds of coal, all of which come under one or other of the following heads: cubical coal, slate coal, cannel coal, glance-lignite,—the last being, as its name implies, an imperfect development of wood; it is a brown coal. We are not here concerned with coal as a fuel. ”

“ The red ash coal burns more freely than the white ash and the ash is heavier and therefore cleaner. The price is higher per ton or bag.
Coal is sorted in different sizes, a medium size being best for the ordinary range. Poor coal has slaty pieces in it, that will not burn but break up and mingle with the ashes. You can learn to detect it by the slaty color. Clinkers are formed by unburnable minerals, mixed with the coal, that35 melt and stick together, and even adhere to the lining or the grate. They are not often troublesome in the cooking range. ”

“ They include coal in veins as shallow as fourteen inches, all coal whose ash content does not exceed thirty per cent, and all known deposits within six thousand feet of the surface. They are based on the optimistic assumption that two-thirds of the coal in the mines will be brought to the surface, a considerably higher recovery than has hitherto been achieved. ”

“ About coal, it should be understood that good hard coal has a glossy black color and a bright surface, whereas poor coal contains slaty pieces. The quality of coal can also be determined from the ash that remains after it is burned. ”

“ 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. ”

“ Substantial improvement also remains to be attained in processing the coal for market, in view of its high ash and moisture content. Unsolved problems also remain in the manufacture of coal briquettes. ”

“ When pit-coal is charred in an oven, called a coke oven, all the bitumen and sulphur contained in it are disengaged, and a charcoal remains, called, however, coke. Wood, when charred is decomposed; all the volatile parts are disengaged with carburetted hydrogen gas, and the woody fibre is converted into coal. This coal is more or less dense according to the compactness of the wood. Hard woods furnish the most solid coal, and light woods on the contrary. ”

“ Where thirty or forty seams of coal have been found one below another, we have evidence of land and water thus changing places many times.
When vegetable matter is excluded from air and under great pressure, it decomposes slowly, parting with carbonic acid gas; and is first changed into lignite or brown coal, and then into bituminous coal, or the soft coal that burns with smoke and flame. I have been in a coal-mine where the carbonic acid gas, pouring from a crevice in the coal, put out a lighted candle. ”

“ In the great coal-field of South Wales, to which we must look for our main supply of anthracite, we are able to trace the action of heat in producing a whole series of different classes of coal in a single seam, which at one part is highly bituminous—soft, flaming coal, like the Wallsend, then it becomes harder and less bituminous, then semi-bituminous “steam coal,” then less and less flaming, until at last we have the hard, shiny form of purely carbonaceous coal, that may be handled without soiling the fingers, and which burns without flame, like coke or charcoal. ”

“ As far as the gas-making properties of the first three are concerned, the relative proportions of carbon and volatile products are much the same. Everybody knows a piece of cannel coal when it is seen, how it appears almost to have been once in a molten condition, and how it breaks with a conchoidal fracture, as opposed to the cleavage of bituminous coal into thin layers; and, most apparent and most noticeable of all, how it does not soil the hands after the manner of ordinary coal. ”

“ When the oxidation has been sufficiently prolonged, anthracite or free-burning coal, as pure as possible, is thrown upon the surface of the metal, and after a short time the thick end of a long birch or oak pole is plunged into the molten mass. This part of the operation is termed ‘poling.’ The wood in contact with the copper is rapidly decomposed; much gas is evolved, which causes the metal to be splashed about, and every part of it to be exposed to the reducing action of the coal. ”

“ Stone coal, Kilkenny coal, Welch coal, and glance coal consist almost entirely of charcoal; and hence, when laid on burning coals, they become red-hot, emit a blue lambent flame, in the same manner as charcoal, and at length are wholly consumed, leaving behind a portion of red ashes. They burn without smoke or soot.
The pitch coal, which has a brownish-black colour, and is generally found massive in plates, the bovey coal, called brown coal, and bituminous wood, with the anthracite coal, and some others of lesser note, form the remaining varieties of coal. ”

“ Chemists tell us that coal is chiefly constructed of carbon, compounded with oxygen, hydrogen, and nitrogen. There are many varieties, but all may be classified under two general headings—bituminous and anthracite. Bituminous coal contains a large amount of a tarry substance, a kind of mineral pitch or bitumen, which burns with a brilliant flame and a black sooty smoke, exceedingly rich in carbon. Anthracite coal is hard and stone-like in its texture, burning with scarcely any flame and no smoke. It produces a fire of intense heat when it is once ignited. ”

“ Mineral coal, however, having been buried in water, mud, and sand, must, almost of necessity, have some mixture of foreign matter, either slate, which is simply hardened mud; silica, which may have been derived from sand; iron and sulphur, some [Pg 101] of which may have been in the wood, but most of it, probably, introduced in solutions; to which should be added, unexpelled oxygen, which is not only useless as fuel, but which combines with a portion of the contained hydrogen, and forms water in the substance of the coal. ”

“ At various points on these acclivities strata of coal have been discovered partly by the action of water, partly by human labour, the extent of which, owing to the impenetrable forest vegetation and the consequent lack of natural indications, can only be ascertained by boring.
The coal is of the best quality of that kind of brown coal generally called cannel coal, and is occasionally met with in immense seams. The average thickness of the seam is about six feet. ”

“ Coal, and all other inflammable fossils, are characterized by their inflammability, insolubility in water, alcohol, and acids, and by their specific gravity, [150] which scarcely exceeds 2, unless loaded with foreign matter. Coal surcharged with bitumen, burns with a bright flame, and, by distillation, affords more carburetted hydrogen gas, which is used for gas light. Common coal, or pitcoal, burns in cakes, more or less, during combustion. Besides charcoal and bitumen, it contains sometimes pyrites, sulphate of iron, and earth. Slate-coal, however, contains more clay. ”

“ At the beginning of the present century the anthracite or stone coal was in general use, in all the districts where it was found, as a fuel for the blacksmith’s fire and the iron worker’s forge. This, however, was the limit of its utility. It was thought to be necessary to force a strong artificial air current up through it to make it burn, and since this could not well be done in grates, stoves, or furnaces, there was no demand for coal for domestic use, or for the great manufacturing industries. ”

“ According to Bischoff, the inflammable gases which are always escaping from mineral coal, and are so often the cause of fatal accidents in mines, always contain carbonic acid, carbureted hydrogen, nitrogen, and olefiant gas. The disengagement of all these gradually transforms ordinary or bituminous coal into anthracite, to which the various names of glance-coal, coke, hard-coal, culm, and many others, have been given. ”

“ The soft coals, on the contrary, being porous as well as soft, allow the gases to escape from them much more readily, and so increase the danger at the working faces of the mines. The gas given out most abundantly by the coal is light carbureted hydrogen, known as marsh gas, from the fact that being a product of vegetable decomposition under water, bubbles of it rise to the surface on stirring the waters of a marsh. This is the gas that is known to miners as fire damp. ”

“ I find them more difficult to be kindled than the Virginia coal, yet a small quantity of dry wood laid on the grate under them is sufficient to ignite them, which being done, they continue to burn while a sufficient amount be added to keep up the combustion, occasionally stirring them to keep down the ashes. They produce no smoke, contain no sulphur, and when well ignited exhibit a vivid bright appearance, all which render them suitable for warming rooms. ”

“ The investigations include the possibility of making satisfactory commercial fuels from lignite or low-grade coals which do not stand shipment well, the benefiting of culm or slack coals which are wasted or sold at unremunerative prices, and the possibility of improving the efficiency of good coals. Some of the various forms of commercial briquettes, American and foreign, are shown in Fig. 2, Plate XX. After undergoing chemical analysis, the coal is elevated and fed to a storage bin, whence it is drawn through a chute to a hopper on the weighing scales. ”

“ Hard coal of good quality has 90 per cent or more of carbon, and burns with little flame. Soft coal contains as much as 18 per cent of flame-making substances, and gives off a heavy smoke. Hard coal is therefore cleaner, but it is more costly than soft coal, because the supply is smaller. The most important anthracite mines are found in the eastern United States, and hard coal is used more in this section than elsewhere. Good hard coal may be recognized by its glossy black color and bright surfaces. It is sold under different names taken often from the locality where it is mined. ”

“ Its structure shows it to consist of the remains of the stems and leaves of plants, reduced to little more than their carbon. Again, some of the coal is made up of the crushed and flattened bark, or outer coat, of the stems of plants, the inner wood of which has completely decayed away. But what I may term the "saccular matter" of the coal, which, either in its primary or in its degraded form, constitutes by far the greater part of all the bituminous coals I have examined, is certainly not mineral charcoal; nor is its structure that of any stem or leaf. ”

“ This fact explains, also, why in mines of wood-coal carbonic acid, i.e. choke-damp, alone is given off. For in the wood-coal a great deal of the hydrogen still remains. In mines of true coal, not only is choke-damp given off, but that more terrible pest of the miners, fire-damp, or explosive carburetted hydrogen and olefiant gases. Now the occurrence of that fire-damp in mines proves that changes are still going on in the coal: that it is getting rid of its hydrogen, and so progressing toward the state of anthracite or culm—stone-coal as it is sometimes called. ”

“ Evaporation by the sun was at one time the sole means of obtaining salt from seawater; now coal is used to boil the salt pans and to purify the brine from the salt-mines in the triassic strata of Cheshire. The extent to which gas is used for illuminating purposes reminds us of another important product obtained from coal. Paraffin oil and petroleum we obtain from coal, whilst candles, oils, dyes, lubricants, and many other useful articles go to attest the importance of the underground stores of that mineral which has well and deservedly been termed the "black diamond." ”

“ The chemical changes which have taken place in the beds of vegetation of the carboniferous epoch, and which have transformed it into coal, are even now but imperfectly understood. All we know is that, under certain circumstances, one kind of coal is formed, whilst under other conditions, other kinds have resulted; whilst in some cases the processes have resulted in the preparation of large quantities of mineral oils, such as naphtha and petroleum. ”