322 MINING FOR COAL 



The most approved arrangement of shafts for a large colliery yielding explosive gas, 

 and where water has to bo pumped, is to sink a shaft for pumping, another for raising 

 coals, and a third for ventilation or upcast ; at the bottom of which is kept burning a 

 large furnace. 



The shaft, as it passes through the earthy cover, should be securely faced with masonry 

 of jointed ashlar, having its joints accurately bevelled to the centre of the circle. 



When the alluvial cover is a soft mud, recourse must be had to the operation ot 

 tubbing. A circular tub, of the requisite diameter, is made of planks from 2 to 3 

 inches thick, with the joints bevelled by the radius of the shaft, inside of which are 

 cribs of hard wood, placed from 2 to 4 feet asunder, as circumstances may require. 

 These cribs are constructed of the best heart of oak, sawn out of the natural curvature 

 of the wood, adapted to the radius, in segments from 4 to 6 foet long, from 8 to 10 

 inches in the bed, and 5 or 6 inches thick. The length of the tub is from 9 to 12 

 feet, if the layer of mud have that thickness ; but a succession of such tubs must be 

 set on each other, provided the body of mud be thicker. The first tub must have its 

 lower edge thinned all round, and shod with sharp iron. If the pit be previously se- 

 cured to a certain depth, the tub is made to pass within the cradling, and is lowered 

 down with tackles till it rests fair among the soft alluvium. It is then loaded with iron 

 weights at top, to cause it to sink down progressively as the mud is removed from its 

 interior. Should a single tub not reach the solid rock (sandstone or basalt), then 

 another of like construction is set on, and the gravitating force is transferred to the 



top. Fig. 1495, represents a bed of quicksand 

 resting on "a bed of impervious clay, that im- 

 mediately covers the rock. A is a finished 

 shaft ; a a, the quicksand ; b b, the excavation 

 necessarily sloping much outwards ; c c, the 

 lining of masonry ; d d, the moating or puddle 

 of clay, hard rammed _in behind the stone-work, 

 to render the latter water-tight. In this case, 

 the quicksand being thin in body, has been kept 

 under for a short period, by the hands of many men scooping it rapidly away as it filled 

 in. But the most effectual method of passing through beds of quicksand, is by means 

 of cast-iron cylinders ; called therefore, cast-iron tubbing. When the pit has a small 

 diameter, these tubs are made about 4 feet high, with strong flanges and bolt holes 

 inside of the cylinder, and a counterfort ring at the neck of the flange, with brackets : 

 the first tub, however, has no flange at its lower edge, but is rounded to facilitate its 

 descent through the mud. Should the pit be of Large diameter, then the cylinders 

 must be cast in segments of 3, 4, or more pieces, joined together with inside vertical 

 flanges, well jointed with oakum and white-lead. When the sand-bed is thick, eighty 

 feet, for instance, it is customary to divide that length into three sets of cylinders, each 

 thirty feet long, and so sized as to slide within each other, like the eye-tubes of a telescope. 

 These cylinders are pressed down by heavy weights, taking care to keep the lower part 

 always further down than the top of the quicksand, where the men are at work with their 

 shovels, and where the bottom of the pumps hangs for withdrawing the surface water. 

 The engine-pit being secured, the process of sinking through the rock is ready to be 

 commenced, as soon as the divisions of the pit formed of carpentry, called brattices, 

 are made. In common practice, and where great tightness of joining is not required, 

 for ventilating inflammable air, bars of wood called buntons, about 6 inches thick 

 and 9 deep, are fixed in a horizontal position across the pit, at distances from each 

 other of 10, 20, or 30 feet, according to circumstances. Being all ranged in the same 

 vertical plane, deals an inch and a half thick are nailed to them, with their joints 

 perfectly close ; one half of the breadth of a bunton being covered by the ends of the 

 deals. In deep pits, where the ventilation is to be conducted through the brattice, 

 the side of the buntons next the pumps is covered with deals in the same way, and the 

 joints are rendered secure by being caulked with oakum, fillets of wood are also fixed 

 all the way down on each side of the brattice, constituting what is called a double pit. 

 When a shaft is to have 3 compartments, it requires more care to form the brattice, 

 as none of the buntons stretch across the whole space, but merely meet near the 

 middle, and join at certain angles with each other. As the buntons must therefore 

 sustain each other, on the principle of the arch, they are not laid in a horizontal plane, 

 but have a rise from the sides towards the place of junction of 1 or 9 inches, and are 

 bound together by a three-tongued iron strap. Fillets of wood are carried down the 

 whole depth, not merely at the joinings of the brattice with the sides of the pit, but 

 also at their central place of union ; while wooden pillars connect the centre of each 

 set of buntons with those above and below. Thus the carpentry work acquires suffi- 

 cient strength and stiffness. 

 In quadrant shafts the buntons cross each other towards the middle of the pit, and 



