Northumberland and Durham. 55 



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 mignt be expected the most tre- 

 mendous 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 Hint 

 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. Buddie, 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. 



