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