fires in a shaft long before the coal-seam is reached by the sinkers; and that the pitmen occasionally open with their picks crevices in the coal or shale, which emit 700 hogsheads of fire damp in a minute. These blowers (as they are termed) continue in a state of activity for many months together, and seem to derive their energy from communicating with immense reservoirs of air. All these causes unfortunately unite in the deep and valuable collieries situated between the great-north road and the sea. Their air courses are 30 or 40 miles in length, and here as might be expected the most tremendous explosions ensue.
The after damp or stythe, which follows these blasts, is a mixture of the carbonic acid and azotic gases resulting from the combustion of the carburetted hydrogene in atmospheric air, and more lives are destroyed by this than by the violence of the fire damp.
To guard against these accidents every precaution is taken, that prudence can devise, in conducting and in ventilating the mines. Before the pitmen descend, wastemen, whose business is to examine those places where danger is suspected to lurk, traverse with flint mills the most distant and neglected parts of the workings, in order to ascertain whether atmospheric air circulates through them. Large furnaces are kept burning at the upcast shafts, in aid of which at Wall's end colliery a powerful air-pump, worked by a steam engine, is employed to quicken the draft: this alone draws out of the mine 1000 hogsheads of air in a minute. A kind of trap-door, invented by Mr. Buddle, has also been introduced into the workings of this colliery. This is suspended from the roof by hinges, wherever a door is found necessary to prevent the escape of air. It is propped up close to the roof in a horizontal position; but in case of an explosion the blast removes the prop, when the door falls down and closes the aperture.
