394 FIRE-DAMP INDICATOR 



acid or choke-damp, which is actually poisonous, so that if a man nhould brontho an 

 atmosphere mixed with it, and be then removed into pure air, ho would not bo capable 

 of resuscitation, for his life is gone; whereas in the case of suffocation by firo-d;mii> it, 

 comes to bo simply a case of suspended animation, for if the lungs bo artificially 

 inflated with pure air before a great expiration of time life may be saved, as in (lie 

 case of persons who have been immersed in water ; hence as a precautionary measure 

 in nil pits where fire- or choke-damp is known to occasionally or habitually bo 

 present, casks of lime-water should be placed at intervals, with coarse cloths suspended 

 in them, so that men in the event of an explosion could seize a cloth as they run from 

 their stall after an explosion, and holding this loosely to their mouths in tho nrmner 

 of a respirator they would find that the lime had removed the carbonic acid, and 

 permitted only tho remaining mixture of air and fire-damp to pass into their lungs; 

 and these gases not being poisonous would enable the men to pass through tho 

 dangerous space occupied by the products of the explosion, and then to reach a place 

 of safety ; whereas if they should fall down and lie in the atmosphere of the explosion, 

 the lime respirator would prevent them being poisoned, and when their bodies were 

 reached by the searchers they would be removed, and tho ordinary means of restoration 

 being applied many would bo recovered, while the searchers themselves would benefit 

 by the aid of the respirators. If fire-damp to tho extent of 5 per cent, be mixed with 

 atmospheric air, and be long inhaled, it produces no remarkable effect, except perspir- 

 ation, which becomes profuse if the amount of fire-damp reach 10 per cent. ; if it still 

 increase to 15 per cent., and be inhaled for half an hour, a peculiar bodily helpless 

 feeling supervenes, which makes one feel disposed to lie on one's back, and the eyelids 

 tingle and smart. These feelings pass off in a few minutes, if fresh air be breathed. 

 In an atmosphere containing 22 per cent, of fire-damp a man may still breathe for 

 some considerable time. The writer of this article remained in such an atmosphere 

 for five minutes making experiments, without other inconvenience than a feeling of 

 mental lassitude other words do not convey the exact sensation ; but in an atmo- 

 sphere more fully charged with fire-damp, probably 33 per cent., ho became helpless 

 before he could determine the amount per cent, present, even in three attempts ; that 

 is, in shorter time than sixty seconds. 



The physical characters of fire-damp vary greatly in different mines ; in some cases, 

 being present to exactly the same amount per cent., it will explode violently in tho 

 lamp with a click, in others quite quietly ; the miners call it a ' sharp gas,' or a 

 ' slow gas,' as the case may be. Its odour varies greatly ; and a circumstance of 

 much importance in another point of view is that its diffusion-rate as regards time 

 varies in different pits ; in one pit it will diffuse into a vessel in forty-five 

 seconds, in another in fifty, while in a third it may take sixty seconds ; the hygro- 

 metric state of the gas appears to cause these variations, for in dry pits tho time is 

 longer, or appeared to be so in these cases, than in pits whose atmosphere was at tho 

 dew point. The writer of this paper is of opinion that tho circumstances attending 

 the production of fire-damp in mines require investigation, as there are many points 

 to be elucidated, by experiments to be made in the pits. 



Fire-damp is a mechanical mixture of carburetted hydrogen, nitrogen, and carbonic 

 acid, in varying proportions. The carburetted hydrogen is the only substance with 

 which we have to deal in fire-damp, because it is this substance that, when mixed 

 with atmospheric air, becomes explosive ; in the act of combustion its carbon forming 

 carbonic acid, and its hydrogen water, both of which at the moment of formation 

 are gaseous, and being at a high temperature, they therefore occupy a larger space than 

 was formerly occupied by the mixed gases : in other words, it explodes, and gives rise 

 to all the phenomena so well known. 



In speaking, then, in future of fire-damp, we allude only to the carburetted hydrogen, 

 or marsh-gas, contained in the mixture, that alone being the combustible substance ; 

 a proposition to be noticed, because our figures will appear to bo different from those 

 obtained by some who have taken tho compound substance. Fire-damp is a chemical 

 compound, otherwise known by tho namo of mine-gas, or as marsh-gas, and is com- 

 posed of one equivalent of carbon, with two equivalents of hydrogen ; it is a light 

 substance of specific gravity 0*559, air being 1*000, and, by its levity, has a tendency 

 to rise to the uppermost part of a gallery. Notwithstanding tho law of diffusion, 

 tho lower contain less than tho upper strata in a chamber, but the writer found, 

 in a return air-way in tho Hetton colliery, a uniform atmosphere of 3 per cent, of 

 fire-damp. It is combustible, forming carbonic acid and water. 



In tho same manner, while speaking of ' choke-damp,' ' after-damp,' ' black- 

 damp,' 'dampie,' &c., wo allude only to tho carbonic acid which is contained in 

 tho compound which passes under so many names, according to tho source whence 

 it occurs, for in all cases it is a mixture of carbonic acid, watery vapour, and nitrogen, 

 in varying proportions. 



