VENTILATION OF MINES 1061 



of the collier, would be laid dead. To obviate this result, double doors are placed in 



three of the galleries adjoining the pit ; viz. at a and b, c and d, e and/; all of -which 



open inwards to the shaft A. By this plan, as the air is not suffered to pass directly 



from the shaft A to the shaft B, through the doors a and b, it 



would have taken the next shortest direction by c d and 2070 



ef; but the doors in these galleries prevent this course, 



and compel it to proceed downwards to the dip-head level 



c, where it will spread or divide, one portion pursuing 

 a route to the right, another to the left. On arriving at 

 the boards g and h, it would have naturally ascended 

 by them ; but this it cannot do by reason of the build- 

 ing or stopping placed at g and h. By means of such 



stoppings placed in the boards next the dip-head level, the air can be transported to 

 the right hand or to the left for many miles, if necessary, provided there be a train or 

 circle of aerial communication from the pit A to the pit B. If the boards i and k are 

 open, the air will ascend in them, as traced out by the arrows ; and after being diffused 

 through the workings, will again meet in a body at a, and mount the gallery to the 

 pit B, sweeping away with it the deleterious air which it meets in its path. Without 

 double doors on each main passage, the regular circulation of the air would be con- 

 stantly liable to interruptions and derangements ; thus, suppose the door c to be re- 

 moved, and only d to remain in the left-hand gallery, all the other doors being as 

 represented, it is obvious, that whenever the door d is opened, the air, finding a more 

 direct passage in that direction, would mount by the nearest channel I, to the shaft B, 

 and lay dead all the other parts of the work, stopping all circulation. As the passages 

 on which the doors are placed constitute the main roads by which the miners go to 

 and from their work, and as the corves are also constantly wheeling along, were a 

 single door, such as <2, so often opened, the ventilation would be rendered precarious 

 or languid. But the double doors obviate this inconvenience ; for both men and 

 horses, with the corves, in going to or from the pit-bottom A, no sooner enter the door 



d, than it shuts behind them, and encloses them in the still air contained between the 

 doors d and c ; c having prevented the air from changing its proper course while d was 

 open. When d is again shut, the door c may be opened without inconvenience, to 

 allow the men and horses to pass on to the pit-bottom at A : the door d preventing 

 any change in the aerial circulation while the door c is open. In returning from the 

 pit, the same rule is observed of shutting one of the double doors before the other is 

 opened. 



When carbonic acid gas abounds, or when the fire-damp is in very small quan- 

 tity, the air may be conducted from the shaft to the dip-head level, and by placing 

 stoppings of each room next the level, it may be carried to any distance along the 

 dip-head levels ; and the farthest room on each side being left open, the air is suffered 

 to diffuse itself through the wastes, along the wall faces, and mount in the upcast pit. 

 But should the air become stagnant along the wall faces, stoppings are set up through- 

 out the galleries, in such a way as to direct the main body of fresh air along the wall 

 faces for the workmen, while a partial stream of air is allowed to pass through the 

 stoppings, to prevent any accumulation of foul air in the wastes. 



In very deep and extensive collieries more elaborate arrangements for ventilation 

 are introduced. The circulation is made active by rarefying the 

 air at the upcast shaft, by means of a large furnace placed either at 

 the bottom or top of the shaft. The former position is generally pre- 2071 



ferred. Fig. 2071 exhibits a furnace placed at the top of the pit. A 

 little way below the scaffold, a passage is previously cut, either in a 

 sloping direction, to connect the current of air with the furnace, or 

 it is laid horizontally, and then communicates with the furnace by 

 a vertical opening. If any obstacle prevent the scaffold from being 

 erected within the pit, this can be made air-tight at top, and a brick e 



flue carried thence along the surface to the furnace. 



The furnace has a, size proportional to the magnitude of the 

 ventilation, and the chimneys are either round or square, being from 

 50 to 100 feet high, with an inside diameter of from 5 to 9 feet at bottom, tapering 

 upwards to a diameter of from 2J feet to 5 feet. Such stalks are made 9 inches thick 

 in the body of the building, and a little thicker at bottom, where they are lined with 

 fire-bricks. 



The plan of placing the furnace at the bottom of the pit is, however, more advan- 

 tageous, because the shaft through which tho air ascends to the furnace at the pit- 

 mouth, is always at the ordinary temperature ; whereas, when the furnace is situated 

 at the bottom of the shaft, its sides get heated, like those of a chimney, through its 

 total length, so that, though the heat of the furnace be accidentally allowed to decline. 



