Anthracite coal in Pennsylvania is subjected to breaking between toothed rollers and an elaborate system of screening, before it is fit for sale. The largest or lump coal is that which remains upon a riddle having the bars 4 in. apart; the second, or steamboat coal, is above 3 in.; broken coal includes sizes above 2½ or 2¾ in.; egg coal, pieces above 2¼ in. sq.; large stove coal, 1¾ in.; small stove, 1 to 1½ or 11⁄3 in.; chestnut coal, 2⁄3 to ¾ in.; pea coal, ½ in.; and buckwheat coal, 1⁄3 in. The most valuable of these are the egg and stove sizes, which are broken to the proper dimensions for household use, the larger lumps being unfit for burning in open fire-places. In South Wales a somewhat similar treatment is now adopted in the anthracite districts.

With the increased activity of working characteristic of modern coal mining, the depth of the mines has rapidly increased, and at the present time the level of 4000 ft., formerly Depth of working. assumed as the possible limit for working, has been nearly attained. The following list gives the depths reached in the deepest collieries in Europe in 1900, from which it will be seen that the larger number, as well as the deepest, are in Belgium:—

Metres.Ft.
Saint Henriette, Cie des Produits, Flenu,Belgium11503773
Viviers Gilly”11433750
Marcinelle, No. 11, Charleroi”10753527
Marchienne, No. 2, Charleroi”10653494
Agrappe, Mons”10603478
Pendleton dip workingsLancashire10593474
Sacré Madame, CharleroiBelgium10553461
Ashton Moss dip workingsLancashire10243360
Ronchamp, No. 11 pitFrance10153330
Viernoy, AnderluesBelgium10063301
Astley Pit, Dukinfield, dip workingsCheshire9603150
Saint André, Poirier, CharleroiBelgium9503117

The greatest depth attained in the Westphalian coal is at East Recklinghausen, where there are two shafts 841 metres (2759 ft.) deep.

The subject of the limiting depth of working has been very fully studied in Belgium by Professor Simon Stassart of Mons (“Les Conditions d’exploitation à grande profondeur en Belgique,” Bulletin de la Société de l’Industrie minérale, 3 ser., vol. xiv.), who finds that no special difficulty has been met with in workings above 1100 metres deep from increased temperature or atmospheric pressure. The extreme temperatures in the working faces at 1150 metres were 79° and 86° F., and the maximum in the end of a drift, 100°; and these were quite bearable on account of the energetic ventilation maintained, and the dryness of the air. The yield per man on the working faces was 4.5 tons, and for the whole of the working force underground, 0.846 tons, which is not less than that realized in shallower mines. From the experience of such workings it is considered that 1500 metres would be a possible workable depth, the rock temperature being 132°, and those of the intake and return galleries, 92° and 108° respectively. Under such conditions work would be practically impossible except with very energetic ventilation and dry air. It would be scarcely possible to circulate more than 120,000 to 130,000 cub. ft. per minute under such conditions, and the number of working places would thus be restricted, and consequently the output reduced to about 500 tons per shift of 10 hours, which could be raised by a single engine at the surface without requiring any very different appliances from those in current use.

In the United Kingdom the ownership of coal, like that of other minerals, is in the proprietor of the soil, and passes with it, except when specially reserved in the sale. Coal lying under the sea below low-water mark belongs to the Ownership of coal. crown, and can only be worked upon payment of royalties, even when it is approached from shafts sunk upon land in private ownership. In the Forest of Dean, which is the property of the crown as a royal forest, there are certain curious rights held by a portion of the inhabitants known as the Free Miners of the Forest, who are entitled to mine for coal and iron ore, under leases, known as gales, granted by the principal agent or gaveller representing the crown, in tracts not otherwise occupied. This is the only instance in Great Britain of the custom of free coal-mining under a government grant or concession, which is the rule in almost every country on the continent of Europe.

The working of collieries in the United Kingdom is subject to the provisions of the Coal Mines Regulation Act 1887, as amended by several minor acts, administered by inspectors Coal Mines Regulation Act. appointed by the Home Office, and forming a complete disciplinary code in all matters connected with coal-mining. An important act was passed in 1908, limiting the hours of work below ground of miners. For a detailed account of these various acts see the article [Labour Legislation].

Coal-mining is unfortunately a dangerous occupation, more than a thousand deaths from accident being reported Accidents. annually by the inspectors of mines as occurring in the collieries of the United Kingdom.

The number of lives lost during the year 1906 was, according to the inspectors’ returns:—

From explosions54
From falls of ground547
From other underground accidents328
From accidents in shafts65
From surface accidents135
——
Total  1129