1873 - Old Forge Coal Mines

INSPECTORS OF MINES. 71
Rule.—To convert Fahrenheit's to Centigrade's deduct 32° and -\- by 18°.
To convert Centigrade's to Fahrenheit's, -f by 18 and plus 32°. To convert
Fahrenheit's to Bearaur's deduct 32° -fby
4, and -=- by 9°. To convert
Beamur's to Fahrenheit's -f- 9°, -f- by 4°, and plus 32°.
A very little practice in these calculations will very soon perfect a person
in this rule, and is undoubtedly correct. The value of the use of this instrument
in mines cannot be too highly recommended in ascertaining the
character and condition of the air by its temperatures.
Barometer. — Its name implies "air meter," by which the weight of the
atmosphere is nicely measured. There are many patterns of barometers in
use, but we only wish in this case to describe the Aneroid instrument, being
the one used by the inspectors of mines. The Aneroid instrument ranges
in size from 2 to 6 inches in diameter, and registers by an index on its
watch-like disk the different changes in i.he atmosphere from stormy,
much rain, rain, change, fair, set fair, to very dry weather. The sweep of
the disk is graduated in inches, from 1 to 31 inches ;
each inch is graduated
into 10,000 parts. The atmospheric pressure upon every square inch of
our globe at the sea level is ascertained to be 14.72 lbs., when the barometer
indicates 30 inches, and the temperature found by the thermometer to
be 60° Fahrenheit, 100 cubic inches of air weighs 30^^ grains avoirdupois,
while 100 cubic inches of water would only weigh 25^ grains. Air of
this density is taken as a standard of density, or the zero of its weight, but
under contrary conditions it weighs heavier when it indicate 31 inches to
15 pounds per square inch, and this weight is adopted ;
but when the instrument
indicates 2S inches the weight per square inch is not so great as
will be observed by a table hereto annexed.
The air grows more lighter as we ascend above sea level, and heaver as
we decend below sea level.
The use of a barometer in coal mines, in connection with the thermometer,
is for the purpose of detecting gases. First—These instruments are
used at the head of the slopes or shafts to ascertain the temperature of the
outside atmosphere by the thermometer, and its weight or gravity by the
barometer. The operator makes note of these conditions, enters the
mine and approaches the district which he desires "to examine. Here he
examines both these instruments and makes note also; then, by the indication
on the thermometer, he sees the temperature of the mine is many degrees
higher than it was found outside. It determines the condition of the
air to be warmer, and consequently expansive in the proportion as shown
by the table. Then should the barometer fall below its outside indication,
or stand at its original point, notwithstanding the depth of the shaft,
it at once indicates the rarity of the air in the mine to be so much lighter,
showing that if the mine air was pure and at such a depth, it ought to indicate
heavier. But when such is not the case, it determines the fact that
under such condition the air is diluted with fire-damp gas, which causes it
to become rarified and lighter, so that the person using the instruments
observes the changes instantly, and declares the
true character of the air,
and by reference to the table may determine its true condition. He then
uses his safety lamp to make the necessary examination of the locality, and
should he find its ventilation defective he would at once direct a remedy
for security. He would then use his anemometer to ascertain the quantum
of air supplied, and if not found satisfactory he would still direct the necessary
increase in the volume of air, sufficient for the removal of the noxious
element, so as to make it safe. He would still continue his explorations
of the other districts of the mine in like manner, making the neeessary
tests and keeping bis notes of the same until the conclusive evidence