COAL MINING. 399 
THE VENTILATION OF MINES. 
The more common gases which are met with in coal mines, are 
known among miners as fire-damp, after-damp or choke-damp, black 
damp, and white damp. TF ire-damp is the light carbureted hydrogen 
gas of chemistry, and consists of one volume of the vapors of carbon 
and two volumes of hydrogen, condensed by affinity into one volume. 
One thousand cubic feet of atmospheric air at the temperature of 32°, 
and a pressure of 14.7 pounds, weighs 80.728 pounds, and one thousand 
cubic feet of fire-damp, under the same conditions, weighs 45.386 
pounds; the weight of the fire-damp is, therefore, .562, as compared 
with common air. Being thus lighter than the atmosphere by nearly 
one-half, it occupies the roof and higher places in mines. In its pure 
and undiluted state fire-damp will neither support light nor life, but 
when mixed with twice its bulk of air it may be breathed, although 
with suffering. Fire-damp requires a mixture of five times its volume 
of air to constitute an explosive compound; with this proportion the 
explosion is very feeble. When a little more than nine times the 
volume of air is added to one volume of fire-damp, it forms a 
powerful explosive mixture. In this condition, the instant a naked 
light is brought into contact with the gas, it explodes with the rapidity 
and violence of gunpowder, and is liable to produce dreadful results. 
When more than fourteen times the volume of air is mixed with the fire- 
damp it again ceases to be explosive. Fire-damp is chemically com- 
posed of— 
By atoms. By weight. By volume. 
EL RODS peeves sec se ceca seve ecole Nueces heseabeSeenseseduels 2 24.6 2 
WAT DOMME eee ecce cose Salt ho sell dacsccusnsbeskaosess 1 15.4 1 
1 100. 1 
After-damp is the product of an explosion of fire-damp, and con- 
tains, when the gas is exploded, 71 parts of pure nitrogen, 9.5 parts of 
carbonic acid gas, and 19 parts of steam. Immediately after explosion 
the steam condenses, leaving a largely increased proportion of carbonic 
acid, which is a most deadly gas. On the occasion of a disastrous 
explosion of fire-damp, more lives are generally lost from breathing the 
after-damp than from the rolling violence of the burning gas. The 
insidious after-damp spreads through the mine, and the miners are soon 
overpowered by the surcharged atmosphere. A painless stupor gradu- 
ally overcomes them, and they fall asleep in death. 
