1816.] On the Ventilation of Coal-Mines. 287 
difficulty. To the proprietors of the mine it is indeed a most serious 
one. ‘The expense is enormous, and success, after all, uncertain. 
This difficulty, however, rests here: the coal can be got at with 
little, if any, danger to the lives of the persons employed in find- 
ing it. 
“Obstacles of a very different nature are met with when the coal 
is found; they are generally in attendance, and commonly present’ 
themselves along with it. These consist of water, which must be 
extracted as fast as it comes in: of two kinds of air, one of which,’ 
if inhaled, instantly suffocates, from which deadly property it has 
obtained from the miners the significant name of choak damp. By 
chemists it is known to be carbonic acid gas. ‘The other kind of air’ 
possesses destructive powers far more extensive. This formidable 
compound in certain circumstances takes fire at the flame of the 
miner’s candle, and explodes with such irresistible force as to dash 
in pieces men, horses, waggons, or whatever may happen to be within 
its range, which not unfrequently extends through all the workings ' 
of the mine. 
This terrible enemy to miners is called by them fire-damp; above 
ground, it is commonly called foul air, which term, it may be re-" 
marked, is extended to all sorts of air which are known to be noxious ' 
or fatal. By chemists this air is termed carlureted hydrogen eas. 
How it is generated has but little reference to the object of this’ 
paper. It is sufficient to observe, that it is found in the workings, 
or cavities left by the workmen in bringing out the coal ; that, if 
not removed, it gradually, and sometimes rapidly, accumulates ; and 
that its firing has often produced most deplorable effects. 
This fire-damp, foul air, or carbureted hydrogen gas, has been 
examined by philosophers; and its distinguishing properties have’ 
been ascertained by experiment. ‘The most striking of these, viz. 
tnflammalility, is found to be restricted to certain conditions. One 
is, that atmospheric, or common air, must be present ; otherwise it 
will not take fire at all. Another, that, though it will burn in open 
air when lighted, as we see in gas lights, yet it will not explode 
unless it amounts to +!,th part of the bulk of common air, with 
which it must also be confined in’ some way, so as to be under com- 
pression. 
Another property of this air is no less remarkable; and that is its 
levity, or comparative lightness. It is among the lightest of all’ 
known substances. Any bulk of ‘it has only about half the weight 
of an equal bulk of common air. Hence its tendency to ascend, 
or rather to be forced upwards, by the pressure of the atmosphere ; 
as a cork, when placed at the bottom of a vessel of water, is forced 
— by the superior weight and pressure of the surrounding: 
id. ; 
This property was lately exemplified in the ascent of Mr. Sadler’s 
balloon from Neweastle, which was filled with a gas nearly of the’ 
same qualities as that which infests more or less the collieries in the, 
neighbourhood, . 
