Reports of the Inspectors of Mines of the anthracite coal regions of ...

INSPECTORS OF MINES. 61
Atmospheric Experiments.
Careful experiments show that 459 cubic feet of air, at 0° or zero of Fahrenheit,
the thermometer indicates 39.76 pounds. When the pressure is 30
inches of mercury, of a density due to 32°, a pressure equal to 14 J pounds
per square inch, which is the ordinary pressure of the atmosphere, but it
only weighs one-thirtieth of this when the pressure is only one inch of mercury.
And since 459 cubic feet of air at 0° expand exactly one cubic foot
for each degree of heat added, we get the following rule to find the weight
of air at any temperature and under any pressure :
Where 1
Thus, 1.3253X1
W=
459+1
= the inches height indicated by the barometer, and t = the
temperature by the thermometer, at 38°, under a pressure of 30 inches of
mercury, 100 cubic feet of air, as per table, weighs just eight pounds. If
225,11(3 cubic feet of air be produced per minute, the temperature in the
downcast to be, say 43|°, and the temperature
211° by the given rule. If the barometer be
in the upcast shaft to be
taken half way down the
shaft, and it to show a pressure of 30| inches of mercury, the weight of a
cubic foot of air, taking the average in the dov^nicast shaft, would be .08044
poundsX900=72,539 pounds upon each square foot by its mere weight,
the upcast air being lighter and only produced a pressure of 54,297 pounds
per square foot, the difference of pressure in both columns of air is=18,099
pounds. In order to find the horse power producing ventilation, we require
to multiply this difference of pressure (18,099 pounds per square foot) by
the number of cubic feet of air produced per minute, and divide the result
by 33,000 pounds, or horse-power, which in this case v;ill give a ventilating
power, thus :
Lbs.
18,099X225,176
=122i horse power.
33,000
Much valuable information may be gained from this method of calculation,
and from the relation the inside and outside temperatures bear to each
other, as when the temperatures are of the same degree of heat natural ventilation
will cease, and artificial means must be applied to create a current
and the ventilating currents should be so arranged that each working panel
should receive its proper proportion of fresh and pure air without stint, and
so well directed up to the working face as to be effective in. removing all
noxious gases and vitiated air from the working men, and to be there conducted
into exit courses to the surface, forced out by steam jet or furnace
power, or drawn out by the section or exhaust fan. Upon good ventilation
depends the health and safety of the workmen, and no valid reason can be
truthfully adduced to excuse defective ventilation. In mines that generate
large bodies of gases too strong a current is not so safe. The miner, in
exploding a charge where fire-damp exists, should be certain that the locality
was free from it, and should use touch-paper only to ignite it, as firedamp
will not, under any ciVcumstance, take fire from a spark. Its character
in this respect differs from powder, which resists the fiame and unites
with the spark, but explosive gas will ignite by a fiash of powder ; and
therefore the act of blasting and discharging shots in dangerous air should
be attended with great circumspection, and by the best practical men. The
custom amongst miners is that each man discharges his own shots, but I
am of opinion it would be much safer on all hands to employ a practical
man or two in large extensive collieries for this purpose.
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