Explosions in Coal Mines. 25 



degree pent up or restrained by the pressure of the atmo- 

 sphere; and the diminution of pressure indicated by a sudden 

 fall taking off this restraint, would let the gas expand and 

 escape more freely, and hence its more abundant appearance. 

 Now, without reference to the fire-damp which would ooze 

 out of the strata and from the surface of the goaf basin, let us 

 for a moment consider what would happen as respects the gas 

 already free, but held by its small specific gravity in the upper 

 part of the basin. The barometer will sometimes sink an inch 

 in twelve hours: on such an occurrence, any portion of air or 

 gas pressed on merely by the atmosphere will expand about 

 one-thirtieth part in that time. The portion of air or gas con- 

 tained in the inverted basin of the goaf is, as has been said, 

 equal to the volume of coal withdrawn beneath, as long as the 

 surface of the country above has not sunk ; but because of the 

 inclination of the coal seam, which we may for the present 

 assume as that at the Haswell Little Pit, the air space which 

 is above the level of the highest point of the edge of the con- 

 cavity may be taken for illustration, as four-fifths of the bulk 

 of the coal, or four-fifths of 1 3 acres by a thickness of 5 feet 

 (2,265,120 cubic feet); of which the one-thirtieth part, or 

 75,500 cubic feet, will by expansion be driven below the level 

 of the highest point of the goaf basin. If it contain any por- 

 tion of gas, it will by its lightness begin to flow out at that 

 particular part; if it contain much, it will flow out the more 

 rapidly, and be the more dangerous ; and if, in a mine much 

 infected with fire-damp, it be an explosive mixture, it is easy 

 to imagine that such a cause may occasionally bring about 

 most fatal results. 



A fall of an inch in the barometer, of a sudden, is rare, but 

 a fall of one-tenth of an inch is not, and that in such a goaf as 

 the one supposed would place 7550 cubic feet below the edge 

 of the cavity; this all tends to issue forth at one place, and 

 that generally a place where the ventilation is weakest. If, 

 as an influential circumstance tending to diminish the quan- 

 tity of issuing atmosphere, we assume that the country above 

 has descended, so as not to leave more air space in the goaf 

 than one-fourth of the volume of coal removed, still that would 

 permit 1887 cubic feet to issue forth at one spot, on the oc- 

 currence of a fall in the mercury of the barometer equal to 

 one-tenth of an inch. Hence it does appear to us that the 

 goaf, in connexion with bai'ometer changes, may in certain 

 mines be productive of sudden evolutions of fire-damp and 

 explosive mixtures, and that the indication of the barometer, 

 and the consequent condition of the mine, ought to be very 

 carefully attended to. 



