Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/94

Rh COAL [MINING. These have been made large enough to supply air to a man with a lamp for an hour, but this is an inconvenient size, being too large to be carried on the back. Fires in Underground fires are not uncommon accidents in coal mines, mines. In the thick coal workings in South Staffordshire the slack left behind in the sides of work is especially liable to fire from so-called spontaneous combustion, due to the rapid oxidization that is set up, when finely-divided coal is brought in contact with air. The best remedy in such cases is to prevent the air from gaining access to the coal by building a wall round the burning portion, which can in this way be isolated from the remainder of the working, and the fire prevented from spreading, even if it cannot be extinguished. When the coal is fired by the blast of an explosion it is often necessary to completely isolate the mine by stopping up the mouths of the pits with earth, or in extreme cases it must be flooded with water or carbonic acid before the fire can be brought under. There have been several instances of this being done in the fiery pits in the Barnsley district, notably at the great explosion at the Oaks colliery in 18G6, when 360 lives were lost. Methods of The drawing or winding of the coal from the pit bottom winding, to the surface is one of the most important operations in coal mining, and probably the department in which me chanical appliances have been brought to the highest state of development. In the simplest case, where the mine is worked by levels, the trains of coal may be drawn from the working faces directly to the level mouth by horse power, or in some exceptional cases locomotives worked by com pressed air are used. In South Wales the power for lifting the load in the shaft is still in some small workings fur nished by a water balance, that is, a box which is filled with water at a high level, and in descending raises the loaded trucks by a rope passing over a pulley at the surface. This method is only available when there is a free drainage level for the water to run off w r hen the box reaches the lowest point. Other hydraulic motors, such as wheels, pressure engines, &c., are used in different locali ties as well as animal power, where the amount of coal to be drawn is small, but as a general rule it is necessary to have recourse to steam power to maintain an adequate output. The old custom of drawing the coals in tubs or hutches (cu/at of the French miner), swinging freely from the end of the drawing rope, is now almost entirely super seded by the adoption of cages sliding between fixed guides, which allow the load to move freely up and down while checking lateral oscillation. This improvement, which is due to Mr John Curr of Sheffield, was originally intro duced in 1798, but made surprisingly little progress for nearly half a century. It was first brought into general use in the North of England, but in many of the smaller pits of the Midland counties the older custom prevailed until recently. The different elements making up the drawing arrange ments of a colliery are (1) the cage, (2) the shaft or pit fittings, (3) the drawing-rope, (4) the engine, and (5) the Cage. surface arrangements. The cage, as its name implies, consists of one or more platforms connected by an open framework of vertical bars of wrought iron or steel, with a top bar to which the drawing-rope is attached. It is customary to have a curved sheet-iron roof or bonnet when the cage is used for raising or lowering the miners, to pre vent them from injury by falling materials. The number of platforms or decks varies considerably ; in small mines only a single one may be used, but in the larger modern pits two, three, or even four-decked cages are used. The use of several decks is necessary in old pits of small sec tion, where only a single tram can be carried on each. In the large shafts of the Northern and Wigan districts the cages are made about 8 feet lon^ and 3 feet broad, being sufficient to carry two large trams on one deck. These are received upon a railway made of two strips of angle iron of the proper gauge for the wheels, and are locked fast by a latch falling over their ends. The guides or conductors in the pit may be constructed Gui of wood, in which case rectangular fir beams, about 3 by 4 inches, are used, attached at intervals of a few feet to buntons or cross-beams, built into the lining of the pit. Two guides are required for each cage ; they may be placed opposite to each other, either on the long or short sides the latter being preferable. The cage is guided by shoes of wrought iron, a few inches long and bell-mouthed at the ends, attached to the horizontal bars of the framing, which pass loosely over the guides on three sides. In some of the large collieries in Northumberland wrought iron guides have been adopted with advantage. They are applied on one side of the cage only, forming a complete vertical railway, light flange rails such as are used for the roadways underground being used instead of wooden rods and iron cross sleepers, with proper seats for the rails instead of wooden buntons ; the cage is guided by curved shoes of a proper section to cover the heads of the rails. Rigid guides connected with the walling of the pit are probably the best and safest, but they have the disadvan tage of being liable to distortion, in case of the pit altering its form, owing to irregular movements of the ground, or other causes, Wooden guides being of considerable size, block up a certain portion of the area of the pit, and thus offer an impediment to the ventilation, especially in up cast shafts, where the high temperature, when furnace ventilation is used, is also against their use. In the Wigan district, wire-rope guides have been introduced to a very considerable extent, with a view of meeting the above objections. These are simply wire-ropes, from f to 1 inches in diameter, hanging from a cross-bar connected with the pit-head framing at the surface, and attached to a similar bar at the bottom, which are kept straight by a stretching weight of from 30 cwt. to 4 tons attached to the lower bar. In some cases four guides are used two to each of the long sides of the cage ; but a more general arrangement is to have three two on one side, and the third in an intermediate position on the opposite side. Many colliery managers, however, prefer to have only two opposite guides, as being safer. The cage is connected by tubular clips, made in two pieces and bolted together, which slide over the ropes. In addition to this, it is ne cessary to have an extra system of fixed guides at the surface and at the bottom, where it is necessary to keep the cage steady during the operations of loading and landing, there being a much greater amount of oscillation during the passage of the cage than with fixed guides. For the same reason it is necessary to give a considerable clearance between the two lines of guides, which are kept from 15 to 18 inches apart, to prevent the possibility of the two cages striking each other in passing. With proper precautions, however, wire guides are perfectly safe for use at the highest travelling speed. The cage is connected with the drawing-rope by short Ro] lengths of chain from the corners known as tackling clia chains, gathered into a central ring, to which the rope is attached. Round steel wire-ropes, about 2 inches in diameter, are now commonly used ; but in very deep pits they are sometimes tapered in section to reduce the dead weight lifted. Flat ropes of steel or iron wire were and are still used to a great extent, but round ones are now gene rally preferred. In Belgium flat ropes of aloe fibre are in high repute, being considered preferable by many colliery managers to wire, in spite of their great weight. In South Staffordshire, flat link chains made with three or more parallel links, with a stud of wood filling up the