THE OPERATIVE CHEMIST. 
368 
part of a bent water-pipe contracts the passage for the 
water, and, at length, stops the current unless propelled 
with great force. 
This method of ventilation has, indeed, been found suc 
cessful when performed in all its detail with accuracy and 
skill, and under the favourable circumstance of being used 
in thin coal-seams containing but little fire-damp. It may 
not improperly be called the Diluting System of Ventilation. 
There is another method in use of clearing mines of fire 
damp by means of what is called the firing line. This 
dangerous operation is performed by an apparatus consist 
ing of a long pole, or a series of poles, fitting one into the 
other, like a fishing rod, so as to be elevated to the break, 
or pit-hole, where fire-damp is accumulated. At the up 
per end of this pole a copper wire is passed through upon a 
small sheave or wheel, which wire is made to reach to any 
distance within the area of the mine from the horse stable. 
This done, the pole is firmly fixed in the place where the 
gas lodges ; the candle fixed to a piece of lead, or other sub 
stance, to keep it steady, is carried by the firemen as far to 
wards the explosive regions as safety will admit of, when it 
is set upon the floor, and fastened to one extremity of the 
upper wire. Afterwards the firemen retire to the stable, 
which is made strong and well secured in order to barricade 
them. The other extremity of the wire is passed through 
a crevice in the door, by which means they draw the wire 
until the light gets to its destination. In some instances 
they remain pent up for a length of time in the greatest 
suspence, owing to some accidental circumstance having 
put the candle out before it reaches the pit-hole. They are 
fearful of coming out from the uncertainty of what may be 
the event. 
In mines where fire-damp is very prevalent, it has been 
found necessary to explode the gas three times a day, at 
each time clearing the mines of all the workmen except 
the firemen. The necessity of this has been occasioned by 
the miners cutting down strata or measures of coal so as to 
render their roof higher than the general run of six or eight 
feet seams, and by these means making the extra elevation 
too great to be effected by the diluting current. In short, 
when the roof of a coal mine, where the seam is thirty-six 
feet thick, is cut down, no means but the firing process 
could hitherto suspend, even for a day, the destructive effects 
produced by an explosion affecting the whole mine. 
The expense of this process is immense, besides the loss