Anthracite

ANTHRACITE. The word "Anthracite" is derived from the Greek avepae€c used in connection with the first mention of coal about 371 B.C., when Theophrastus, a pupil of Aristotle, men tions in his treatise "On Stones" fossil substances (Xt06s avOpaKos) "that are called Coals which kindle and burn like wood coals. . . . These are found in Liguria and in Elis, in the way to Olympias over the mountains ; they are used by the smiths." The word is now applied to that class of coal which contains the highest percentage of fixed carbon, and belongs to the division A (I) in the classification adopted by the International Geological Conference held at Toronto, Canada, in the year 1913 (see COAL AND COAL-MINING) ; a class of coals the mean composition of which is: Carbon . . . . . . . . . . 93 to 95% Hydrogen . . . . . . . . 2 to 4% Oxygen and nitrogen 3 to 5% with a calorific value ranging from 14,500 to 15,000 B.T.U. or 8,000 to 8,33o calories.

Anthracite is usually a hard compact coal having a sharp con choidal fracture, in colour black with a brilliant lustre, and, unlike other coals, except cannel, does not usually soil the fingers when handled. Some varieties differ somewhat from this description, being dull and when fractured breaking into small cubical lumps. The best grade of Welsh anthracite (and the finest anthracite in the world comes from that principality) contains 93% or over of fixed carbon and less than 8% of volatile hydrocarbons. The fact of the high percentage of fixed carbon and the very low volatile hydrocarbon content renders the coal smokeless. For the same reason it is very difficult to ignite, owing to which fact it is un suitable for burning in the open grate and for steam raising unless under forced draught.

The table at head of the opposite page gives the proximate and ultimate analysis of some anthracites.

The specific gravity of anthracite is usually higher than that of bituminous coal, ranging from 1.36 to 1.84 as compared with 1.2 to 1.5 in the case of bituminous coal. The calorific value of anthracite is, as is evident from the figures already quoted, very high. A high-class anthracite may, for instance, have a calorific value of 8,624 calories, which is equivalent to an evaporative power of 16•o6 lbs., that is to say, 16•o6 lbs. of water would be evaporated by the combustion of I lb. of such anthracite. The volatile hydrocarbon in anthracite, including under that term semi-anthracites, as well as pure anthracite, ranges from 12 to 4%.

Taking the ratio : I the proportion in the case of Vol. H. C.

semi-anthracite is from 12 : I to 8 : 1; hard dry anthracite from 5:I to io: I.

Origin of Anthracite.

It was generally considered by geol ogists that anthracite was metamorphosed bituminous coal, that is, coal from which the greater part of the volatile hydrocarbon had been driven off by heat, occasioned by the pressure resulting from earth movements or due to the proximity of intrusive igneous rocks. But of late some doubt has been thrown on this as the only explanation of the low volatile content. One has seen, e.g., in Natal and Zululand, anthracite which has resulted from the action of the heat derived from neighbouring intrusions of igneous rock, baking the coal and reducing the volatile contents. One consequential effect of this action of heat is the increase in percentage of the ash content as compared with the unindurated coal. But in the South Wales field, where we find bituminous coal seams in the east of the field in their passage westwards graduating into steam coals, dry steam coals, and finally into anthracite, not only does the ash content not increase but it actually diminishes. So it is very doubtful whether heat generated by the somewhat more intensified folding to which the seams to the west have been subjected, as compared with the same seams in the east, is the sole cause, if even a partial cause, of the dis appearance of a great part of the volatile hydrocarbons from the coal. The folding was probably a slow process, continuing over years, and the heat would be dissipated without greatly affecting the coal. The more probable explanation is that the effect is the outcome of bacterial action on the vegetation which was of a somewhat different kind from that in the lower lying surface, though continuous therewith, and was longer above water than the latter, allowing of more extensive bacterial action. (See COAL AND COAL-MINING: Origin and Occurrence.) For information relative to the available resources of anthra cite in the world, by continents, the reader is referred to COAL AND COAL-MINING : The World's Coal Reserves, Output, Consump tion, etc., from which it will be seen that in this respect Asia stands first. Seventy-five % of the anthracite of Asia is contained in the province of Shansi, south-west of Peking, China, and there is probably in the small coal-field near Tongking in French Indo China as much anthracite as there is in Pennsylvania. Of the European fields, that of Donetz, in South Russia, contains most anthracite. The coal-fields of the U.S.A. contain 19,684 millions of tons of anthracite, the Canadian resources amounting to only 2,18;, millions of tons.

Chief Supplies.

The chief producers of anthracite in the world are Great Britain and the U.S.A. The output from the former has been steadily on the increase of late years, in 1925 reaching 6,184,191 long tons, whereas the tendency of the output of this class of coal in the U.S.A. has been downwards. In the year 1917 it reached the enormous figure of 88,939,117 tons as against 83,338,401 tons for 1923; 78,506,217 tons for 1924; and for 1925 (a strike year) 55,193,883 tons.

In America the use of anthracite as a fuel for domestic use is much more in favour than in Great Britain. Some American cities enjoy a beautifully clear atmosphere owing to the smokelessness of the fuel, though of late bituminous coals have come more and more into vogue because of their cheapness. Were the people of Great Britain wishful of imitating their American cousins in this respect, many more anthracite mines than at present exist in South Wales, and, to some extent, Scotland, would have to be opened out, and the available resources, which are greatly less than those of the more bituminous coal, would be rapidly exhausted. In Great Britain an open and "flaming" fire is most popular, and anthracite stoves are used only for central heating. Besides the domestic consumption, which is the chief use to which anthracite is applied, it is largely used for malting purposes and for the dry ing of hops, where a steady heat is required, for which purpose the anthracite must be free from arsenic. It has been and still is used to some small extent (though not in Great Britain) for iron-smelt ing. There is also a growing consumption in the production of producer gas.

Of the production of anthracite in Great Britain, 6o% is ex ported, her market being chiefly France and Scandinavia; but latterly Canada, whose import requirements are variable—between 3,000,00o and 4,000,00o tons per annum— has become a customer, though her demands are chiefly met from Pennsylvania. The higher quality, however, of the best Welsh anthracite and the water carriage from Swansea and Llanelly to Montreal are points which are beginning to tell strongly in favour of South Wales anthracite.

Anthracite is of all coals that which undergoes most classifica tion for the purposes of marketing. To take a characteristic ex ample from a modern Welsh anthracite mine the coal is divided by screening and working into the following brands or classes, viz.:— In some American anthracite mines the division of the output is carried out to a still greater extent, even to 3o classes or more.

According to the classification of coal adopted by the United States Geological Survey the ratio of fixed carbon to volatile mat ter for anthracite should equal or be above ten. It would appear that anthracite may degenerate in the process of geologic time and absorb moisture. M. R. Campbell of the United States Geological Survey has called such coal "super-anthracite" as ex pressing increased metamorphosis rather than improved quality and more desirable characteristics. This super-anthracite is found in Rhode Island. It burns with the greatest of difficulty and has a low calorific value, all of which keeps it from having, at present, any extensive sale.

The definition of anthracite as coal having a fuel ratio above ten is not the same as that for class Ai, which was evidently intended for anthracite when adopted by the twelfth international geological congress in 1913. There the lower limit was 12. Con sequently it may be stated that the designation used in the United States is somewhat broader than that of class Ai. That congress also designated a class A2 which was evidently intended to con stitute semi-anthracite. Its fuel ratio ran between 7 and 12 whereas the United States geological survey's practice is to limit semi-anthracite by the ratios 5 and io. In coal trade the word anthracite has had a broad meaning, those producing and selling what is known as semi-anthracite objecting to the use of any qualifying term in describing their product. Consequently coal with a fuel ratio as low as five, or even slightly less, is sometimes quoted as anthracite.

Distribution.

Disregarding the Rhode Island coal there are only four areas in the United States containing marketable quan tities of anthracite. These are (I) a part of the so-called "anthra cite region" of north-eastern Pennsylvania, (2) a small area at Fioresta, Gunnison county, Colo., and areas in the (3) Bering river and (4) Matanuska regions of Alaska.

The first of these three districts is by far the most important. The entire area, including both anthracite and semi-anthracite, covers 484sq.miles. The Sullivan county field around Bernice, Pa., produces semi-anthracite, as does the Lykens valley end of the southern coalfield. Some of the northern anthracite field is close to the border line of semi-anthracite. However, there are parts of the southern field which contain the most highly anthracitized beds. In general the northern coalfield is but gently folded. The principal disadvantage under which it is worked is the presence of the Wyoming "buried valley': which is filled with glacial drift. This valley imposes upon the measures below it a burden of as much in places as 2ooft. of unconsolidated sand and gravel. Fur thermore, the bottom is scored with pot holes which were formed under the ice during the glacial period. Heavy, lacking strength and filled with water, these glacial deposits make the mining of the measures—especially where they are relatively shallow— quite hazardous. The eastern middle and southern fields are badly contorted and faulted. Because of this contortion the coal is dense and hard, and has a high fuel ratio.

The coal of the Pennsylvania anthracite region is of the Carbon iferous era though the correlation between the coals of the region and those of the bituminous fields in other parts of Pennsylvania is by no means satisfactory and the names used for the various beds are not the same.

The seams of coal are of all thicknesses from 114f t. downward. This extreme thickness was found in Nesquehoning slope No. 9 of the Lehigh Coal and Navigation Company. Some coal as thin as 18in. has been mined and much of the coal operated is under aft. thick. According to F. G. Tryon and M. H. Schoenfeld, U.S.

Bureau of Mines, the average coal thickness of United States anthracite is 8oin. and of all British coal 5oin., basing the latter figure on the 1925 report of the royal commission. Most of the coal is drilled and blasted out of the solid. Undercutting machines are successfully used, where the inclination of the coal bed is not too great, but the proportion is small. Shaking conveyors are used, especially in the thin seams and in seams pitching so gently that the dislodged material cannot be chuted from face to gang way. In thin flat seams the coal is often dragged to the roadway by small scoops of a capacity of about 1,00o pounds. These scoops, which are bottomless and have one open end, are dragged by ropes through the pile formed by the coal shot from the face or pillar to a chute at the roadway, where the coal they contain is dis charged into the mine cars.

Gas.

Few if any mines are more gassy than those in the Wilkes Barre region. Fortunately, with ventilation such as is provided, the area which becomes filled with an explosive quantity of gas is rarely large. In consequence there have been no explosions involving as many victims as the larger ones in the bituminous regions where the coal dust has extended some disasters and even initiated others. Anthracite dust is not absolutely inert in an explosion but it has almost no explosive effect. However, N. H. Darton, writing as of 1912, declared that "The volume of methane issuing from three mines at Wilkes-Barre is 9.0oo,000cu.ft. a day, a volume equal to that of the illuminating gas from a plant supplying a city of 300,00o inhabitants." Fires.—When anthracite beds are ignited the combustion is extinguished with great difficulty and many extensive fires have occurred. Many still burn and notable among these is a fire at Summit Hill, one in the Red Ash bed near Wilkes-Barre and one at Carbondale.

Reserves.

Marius R. Campbell has estimated that the original quantity of anthracite and semi-anthracite in the Pennsylvania anthracite region was 19,056,300,000 metric tons. The total pro duction to the end of 1938 was 3,874,819,00o metric tons. Doubling this for coal irremedially wasted underground and above ground the tonnage remaining will be 11,306,662,00o metric tons. Assuming that 50,000,000 net tons will be mined yearly and that by more careful methods the loss will be cut to one-half of the production, the yearly depletion will be about 75,000,00o metric tons and the life of the anthracite field will be i 5o years from the end of 1938, assuming that the various estimates quoted are at least approximately correct. Some of the measures have been but little explored and are none too well understood. Nor is it possible to form an adequate conception of the waste in the past or to predict the probable waste in the future. The annual tonnage may also increase or decline with the passage of years. Much of what was formerly wasted is being recovered but much has been lost beyond recovery through squeezes and fires, so the estimate of past waste has intentionally been made high.

The seams worked are becoming progressively lower and deeper, increasing the difficulty of operation. The shaft collar of the Auchincloss shaft No. 2 of the Glen Alden Coal Company, is 7 21.5f t. above sea-level. Its deepest working is 9 7 7f t. below the sea making a total depth of 1,698.5 feet. The West Brookside workings are probably deeper. The average depth of shafts in the shaft mines of the anthracite field is given by F. G. Tryon and M. H. Schoenfeld as 415ft. as against 1,o23ft. for all mines of Great Britain. The figure for Great Britain is taken from the report of the royal commission (1925). Much coal, however, still comes in the anthracite region from shafts and drifts.

According to E. W. Parker: "The first authentic knowledge of the anthracite deposits in Pennsylvania was obtained in 1762 when it was discovered by Connecticut pioneers. The value of this discovery was made known by Obadiah Gore, a blacksmith, who set up a forge in 1770 or 1771 and used anthracite for heating iron. During the Revolutionary War some anthracite was floated down the Susquehanna river to a point near Harrisburg and thence hauled to Carlisle, where it was used for making munitions of war for the Continental army." In 18o8 anthracite was first used in an open grate by Jesse Fell, of Wilkes-Barre, and in the same year Abijah Smith and Company shipped several arkloads to Columbia and other points on the Susquehanna river. Anthra cite was first used in an iron furnace in Philadelphia in 1812.

Markets.

The market for American anthracite has gradually contracted in area and, of late years also, as to tonnage. Bitu minous coal has displaced anthracite in the West due partly to re strictions during the World War. An effort was made to restore this market. In the East oil competition has been quite severe, ow ing partly to the low cost of fuel oil. As a result the output is no longer limited as before by strikes, local and general, and by physical inability to increase production but by the variation of the market. The output in 1917 was 99,612,000 net tons; in 1927 it was 80,096,00o tons, and in 1937 was only 51,856,000 tons. There has been a great increase in the demand for small sizes. Formerly every size below chestnut was unsaleable ; in 1937 48% of the sales is pea or smaller. Practically no lump is sold; in 1937 "broken" was 0.4% of the total tonnage ; "egg," 5.4%; stove, 21.2%; chestnut, 25.2%; pea, I0.7%; buckwheat No. 1, 14.8%; buckwheat No. 2, or rice, 8.3%; buckwheat No. 3 or barley, i o•3 % ; buckwheat No. 4, 2.9% ; all others, o.8%. Care is taken in breaking down the larger and less saleable sizes such as "lump," "broken" and even "egg," not to make an unnecessary proportion of fine sizes which bring a price, at the breaker, below the cost of mining. The demand that has been stimulated for fine sizes by the development of the automatic stoker is satisfied partly by the rewashing of old piles of coal formerly rejected, which con tain millions of tons of good fuel, some even larger than chestnut, and partly by dredging formerly discarded fines from the river bottoms.

Smaller anthracite occurrences are found at Cerrillos, N.M., due to the intrusion of an igneous sill 4oft. below the coal measure, also in Routt county, Colo.; Iron county, Utah; and Pierce county, Washington.

Semi-anthracite.

Other commercial bodies of coal, fre quently marketed as anthracite, are found in Virginia and Ar kansas. Strictly speaking these are semi-anthracite. When a coal falls into the semi-anthracite grouping that fact hardly makes it less desirable, for a little volatile matter will not make the coal smoky, but it will render it somewhat more free-burning and cause it to give a bright yellow flame, thus making it attractive as a grate fuel. Semi-anthracite also ignites more readily than anthracite. On the other hand, a furnace burning anthracite is more easily regulated than one burning the less matured fuel. The differences are small and the two types of coal are closely competitive, wherever they are so located as to enter the same markets.

The semi-anthracite of Virginia is of lower Carboniferous age and extends in a narrow band across the counties of Montgomery, Pulaski and Wythe. The principal bed runs from 4 to 2oft. in thickness. In these coals there is a large percentage of ash. The beds are quite severely contorted. The Arkansas semi-anthracite is found in Franklin, Johnson, Pope, Sebastian and Logan counties in thin beds. (R. D. H.; X.) See H. S. Raushenbush, Anthracite Question (5924) ; J. K. Mum ford, Anthracite (1925) .