MINING FOE COAL 821 



yards into the rock, the gallery or drift may then be pushed forward to the point D, 

 when the shaft E D is put down, after it has been ascertained by boring that the rock- 

 head or bottom of the quicksand at F is a few yards higher than the mouth of the 

 small pit B. During this operation, all the water and mine-stuff are drawn off by the 

 pit B ; but whenever the shaft E D is brought into communication with the gallery, the 

 water is allowed to fill it from c to D, and rise up both shafts till it overflows at the 

 orifice B. From the surface of the water in the deep shaft at o, a gallery is begun of 

 the common dimensions, and pushed onwards till the coal sought after is intersected. 

 In this way no drainage-level is lost. This kind of drainage-gallery, in the form of 

 an inserted syphon, is called a drowned or a blind level. 



When a coal-basin is so situated that it cannot be rendered level free, the winning 

 must be made by the aid of machinery. The engines at present employed in the 

 drainage of coal mines are : the water-wheel, the water-pressure engine, and tho 

 steam-engine. See HYDRAULIC MACHINERY. 



The depth at which the coal is to be won, or to be drained of water, regulates the 

 power of the engine to be applied, taking into account the probable quantity of water 

 which may be found, a circumstance which governs the diameter of the working barrels 

 of tho pumps. Experience has proved, that in opening collieries, even iu new fields, 

 the water may generally be drawn off by pumps of from 10 to 20 iuches diameter ; 

 excepting where the strata are connected with rivers, sand-beds filled with water, or 

 marsh-lands. As feeders of water from rivers or sand-beds may be hindered from 

 descending coal-pits, the water proceeding from these sources need not be taken into 

 account ; and it is observed, in sinking shafts, that though the influx which cannot be 

 cut off from the mine may be at first very great, even beyond tho power of the engine 

 for a little while, yet as this excessive flow of water is frequently derived from tho 

 drainage of fissures, it eventually becomes manageable. The pumping machinery of 

 a new colliery should be adequate to pump the water in 8 or 10 hours out of the 24. 

 In the course of years many water-logged fissures come to be cut by the workings, and 

 the coal-seams get excavated towards tho outcrop, so that a constant increase of water 

 ensues, and thus a colliery which has been long in operation, frequently becomes 

 heavily loaded with water, and requires the action of its hydraulic machinery both 

 night and day. 



Of Engine-pits. In every winning of coal, the shape of the engine-pit deserves 

 much consideration. For shafts of moderate depth, many forms are in use ; as circular, 

 oval, square, octagonal, oblong-rectangular, and oblong-elliptical. In pits of incon- 

 siderable depth, and where the earthy cover is firm and dry, any shape deemed most 

 convenient may be preferred ; but in all deep shafts, no shape but the circular should 

 be admitted. Indeed, when the water-run requires to be stopped by tubbing or cribbing, 

 the circular is the only shape which presents a uniform resistance in every point to the 

 equable circumambient pressure. The elliptical form is the next best, when it deviates 

 little from the circle ; but even it has almost always given way to a considerable 

 pressure of water. The circular shape has the advantage, moreover, of strengthening 

 the shaft walls, and is less likely to suffer injury than other figures, should any failure 

 of the pillars left in working out the coal cause the shaft to be shaken by subsidence 

 of the strata. The smallest engine-pit should be ten feet in diameter, to admit of tho 

 pumps being placed in the lesser segment, and the coals to be raised in the larger one, 

 as shown in fig. 1492, which is called a double pit. If much work is contemplated in 

 drawing coals, particularly if their masses bo large, it would be advantageous to make 

 the pit more than 10 feet wide. When the area of a shaft is to be divided into three 

 compartments, one for the engine-pumps, and two for raising coals, as in fig. 1493, 

 which is denominated a triple pit, it should be 12 feet in diameter. If it is to be 

 divided into four compartments, and made a quadrant shaft, as in fig. 1494, with one 

 space for the pumps, and three for ventilation and 

 coal-drawing, the total circle should be 15 feet in 

 diameter. These dimensions are, however, governed 

 by local circumstances, and by the daily discharge 

 of coals. 



If there is a large quantity of water to pump, it 

 is most desirable to appropriate a shaft exclusively 

 for the purpose. Another shaft being used for raising coal, and as an upcast for the 

 ventilation of the mine. 



When only one shaft is sunk, and divided by wood or stone partitions, the ventila- 

 tion of tho mine is dependent upon these slight divisions of the shaft. If the parti- 

 tions of a shaft become injured or burnt, which has been the case with wood partitions, 

 the ventilation of the mine may suddenly be destroyed. Many lives have been placed 

 in great jeopardy by the burning of wood partitions, which has destroyed the ventila- 

 tion and prevented escape up the shaft. 



VOL. III. Y 



