VENTILATION OF MINES 



1067 



shaft, the circular brickwork of each forming a partition of double thickness and 

 secure strength, from the two arches abutting agtiinst each other. 



The gate-road c. is driven from the shaft at the bottom of the coal, as in the ordinary 



plan; but the air-head din driven from the air-chimney "within 2 feet of the top of the 

 coal, or higher, if practicable, and runs into the vertical air-chimney. The gate-road 

 and air-head are carried forward in a parallel direction to the extent of the work, as 

 before described in the ordinary system; and 'spouts' or openings, e, are driven 

 upwards to connect them, at about every 15 yards every spout being bricked up 

 close, in succession, when a fresh one is made in adA*ance, so as to make the current 

 of air traverse the whole extent of the gate-road before it rises up to the air-head and 

 passes away to the air-chimney. 



In the ordinary system of ventilation, it is manifest that only a very slight deter- 

 mining power compels the air to travel constantly in the same direction. Its current 

 is, at all times, weak and insufficient, and liable to be deranged by the action of the 

 wind, or atmospheric changes ; and it is under no command whatever. To ensure 

 safety a constant current of air is indispensably necessary ; it should be a current, too, 

 maintained by natural causes, as far as possible, and never interrupted, for the reasons 

 already assigned ; and should be one that would not vary or fail. 



To effect this, the ascending column of air must be rendered specifically lighter 

 than the air of the descending column, which circulates through the workings ; and 

 this difference of specific gravity must be maintained constantly free from disturbance 

 by accidental causes, and to such an extent as to produce under all. circumstances 

 a total amount of propelling power that is found sufficient for the complete ventilation 

 of the mine. This is accomplished by conducting the whole of the gas in a continuous 

 ascending column, free from interruption or disturbance, up the separate air-chimney ; 

 and this ascending power is further increased by erecting a ventilating chimney 

 (shown by dots in the vertical section), of a sufficient height, on the surface of the 

 ground, into the base of the air-chimney is continued so as to form one uninterrupted 

 air-flue, from the top of the ventilating chimney down to the air-head in the seam 

 of coal. 



Ventilation is nowhere exhibited to such advantage as in the coal-mines of 

 Northumberland and Durham, where they have carried well nigh to systematic perfec- 

 tion the plan of coursing the air through the winding galleries. 



In Mr. Spedding's system the whole of the return air came in one current to his 

 rarefying furnace (see letter c, fig. 2084), whether it was at the explosive point or not. 

 This distribution was often fraught with such danger, that a torrent of water had to be 

 kept in readiness, under the name of ' the waterfall,' to be let down to extinguish the fire 

 in a moment. Many explosions at that time occurred, from the furnaces below, and 

 also down through tubes from the furnaces above ground. 



About the year 1807 Mr. Buddie had his attention intensely occupied with this 

 most important object, and then devised his plan of a divided current, carrying that 

 portion of the air which, descending in the downcast pit A, coursed through the 

 clean workings, through the active furnace c, fig. 2084, and the portion of the air 

 from the/o workings up the dumb furnace D, till it reached a certain elevation in B, 

 the upcast pit, above the fireplace. The pitmen had a great aversion, however, at first 

 to adopt this plan, as they thought that the current of air by being split would 

 lose its ventilating power ; but they were ere long convinced by Mr. Buddie to tho 

 contrary. He divided the main current into two separate streams, at the bottom of 

 the pit A, as shown by darts in the figure ; the feathered ones representing that part of 

 the pit in which the course of the current of air is free from explosive mixture, or 



