1879.] Influence of Coal-dust in Colliery Explosions. 411 



damp explosion or the blown-out shot, will be inflammable if it con- 

 tain any larger proportion of fire-damp than 0*892 per cent., and the 

 flame of the original explosion will pass on through it, extending the 

 area of the disturbance as far as the same conditions exist, or, it may 

 be, to the utmost limits of the workings. If it contain more than 

 0*892 per cent, of fire-damp, it will be more and more explosive, 

 according as the proportion of fire-damp is greater, until a maximum 

 point is reached, beyond which its explosiveness will begin again to 

 decline. If, lastly, it contain less than 0*892 per cent, of fire-damp, 

 or even if it consist only of coal-dust and pure air, it will still be so 

 nearly inflammable that it will probably become so when it undergoes 

 the compression and consequent heating which the occurrence of an 

 explosion in one part of a confined space must necessarily produce 

 throughout the remainder of the same space. It is probable, more- 

 over, that some kinds of coal-dust require less fire-damp than others 

 to render their mixture with air inflammable ; and it is conceivable 

 that still other kinds may form inflammable mixtures with pure air. 



I have partially investigated the relation between the proportions 

 of air, coal-dust, and gas* required to insure inflammation or ex- 

 plosion on the application of a light ; but as the series of experiments 

 is not yet complete, I propose to reserve their description for some 

 future opportunit}^. I may mention, however, that in the apparatus 

 which I have hitherto employed, the proportion of coal-dust which 

 gave the best results was much larger than might at first sight be 

 thought necessary, namely, about one ounce of dust to a cubic foot of 

 air for all mixtures of gas and air, ranging between one of gas and 

 twenty of air, and one of gas and forty of air. Also, in one of the 

 experiments with the return air of a mine, which I propose to 

 describe in this place, the air requires to be literally black with dust 

 before it will ignite. It is, therefore, obvious that the particles which 

 are floating about in the air of a dry mine, in its normal state, cannot 

 render it inflammable ; and it is probable that only the sweeping' 

 action of a gust of wind, like a squall, passing along the galleries, can 

 raise a sufficient quantity to do so. 



Some of the colliery explosions which have occurred during the 

 last two years are amongst the most disastrous on record, and the 

 attempts that have been made to explain them are of the usual un- 

 satisfactory character. The assumption, without a vestige of proof 

 that fire-damp has suddenly burst from the strata, is still maintained 

 even in cases in which the flame is seen to have ramified into 

 the extremity of every cul-de-sac and extended to the opposite- 

 boundaries of the workings. The very token whereby the ubiquity 

 of the flame is made manifest, is the so-called charring of the timber, 



* As these experiments were only preliminary ones made chiefly for the purpose 

 of testing the apparatus, common lighting gas was employed in them. 



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