1867.] The Ventilation of Coal Mines. 193 



and abroad. Formerly, those with curved blades, arranged so as 

 to discharge the air inspirated from the entire circumference 

 simultaneously, were used in the North of France j but the small 

 effect given by them, when compared with the power expended, has 

 led to their abandonment, and at present the simple forms with 

 straight blades and slightly eccentric drums, similar to the older 

 forms of foundry fans, though, of course, of much greater dimen- 

 sions, are mostly in vogue. The following are among the more 

 important examples : — 



Nasniyth's fan, at Abercarne, has eight wrought-iron radial 

 arms, carrying thin sheet-iron blades 3J feet wide and 3 feet long, 

 the effective diameter is 13^ feet, the drum, or casing, is open all 

 round, and has two passages in the centre for the admission of the 

 air drawn from the mine. It is driven by a single high-pressure 

 engine, of 12 inches diameter of piston and 12 inches length of 

 stroke, and when making from 60 to 90 revolutions per minute, 

 aspirates from 45,000 to 56,000 cubic feet of air per minute, under 

 a pressure of from 0*5 to 0*9 inch of water. 



In Guibal's fan, which is extensively used in the North of 

 France, and has also been introduced in the northern coalfield 

 of England, at Elswick and Pelton collieries, the outlet of the drum 

 is provided with a shifting lip, in order that the area of the 

 aperture through which the discharge takes place may be increased 

 or diminished according to the speed of the arms. Another 

 improvement consists in the use of a tapering chimney with an 

 increasing section, in order to diminish gradually the velocity of 

 the air leaving the fan before it reaches the external atmosphere, 

 whereby a considerably increased pressure is made available, which, 

 under ordinary circumstances, is lost when the air is thrown out at 

 the circumference at an unnecessarily high speed. The construc- 

 tion of the fan offers no special peculiarities. Six arms are usually 

 employed ; but for the largest size it is proposed to increase the 

 number to eight ; the diameter varies from 22 to 30 feet, and 

 the breadth of the arms from 7 to 13 feet. The amount of air 

 drawn per minute is about 105,000 cubic feet, at a pressure varying 

 from 1^ to 3 J- inches of water. 



Such are the means which have been adopted to urge currents 

 of air, with rapidity sufficient to sweep from all the passages of the 

 mines any accumulations of fire-damp. Yet, notwithstanding all 

 the attention which has been given to this matter, we are con- 

 stantly hearing of the most disastrous explosions. Nearly all of 

 these may, however, be referred to carelessness — sometimes so gross 

 as to amount to wilfulness — on the part of the colliers. Naked 

 lights may be forbidden, safety-lamps may be locked, and all 

 possible care taken to secure the proper amount of ventilation, 

 After all, a man or a boy leaves a door open, and thus deranges the 



vol. iv. o 



