18S2.] on Some of the Dangerous Properties of Dusts. 109 



the foregoing, to demonstrate experimentally that the existence of a 

 very small proportion of fire-damp in the air of a mine may determine 

 the propagation of flame by coal dust, ignited by the explosion of some 

 local accumnlation of a ^as mixture, or bv the inflammation of eras 

 snddenlv disenorased. or even bv the flash from a blown-ont shot. It 

 has also been clearlv established that in so-called fierv mines the air 

 is never likely to be actually free from fire-dampj and that as much 

 as 2 per cent, may exist in the return air of a very efficiently 

 ventilated mine of that class. It must therefore be re^arde<i as a 

 thoroughly well-crronnded conclusion that, in manv disastrotLS ex- 

 plosions, coal dust is the chief agent of destruction, and it is in- 

 disputable that but few explosions occur of which the effects have not 

 been more or less considerably extended and a2crravate«i bv the coal- 

 dust which is raised by the fire-damp explosion. It may also be 

 admitted as not improbable that in some instances, the influence of 

 dust may, apart from its combustibility (as described), determine the 

 ignition of a mixture of air and dust with a small proportion of fire-damp, 

 bv the flame which a blown-out shot, or the accidental isrnition of some 

 local accumulation of explosive gas mixture has produced. Lastly, it is 

 conceivable, as contended by Friere IMarreco. Galloway, and some 

 continental observers, that a mixture of an inflammable coal dust and 

 air, may even, in the complete absence of fire-damp, both originate and 

 carry on to some distance, explosions which, though much inferior in 

 violence to those developed throush the asencv of gas mixtures, will 

 be at least equal to them in regard t-o the disastrous effects on the 

 lives of those exposed to them. That mixtures of coal dust and air 

 alone may have the power to carry on the explosion originally caused 

 and disseminated bv a sas, air. and dust mixture, into regions where 

 no gas whatever exists, will now be generally admitted. The great 

 disturbance of the air which must proceed in immediate advance of 

 the rush of flame produced by the ignition of a mixture of gas and air 

 charged with coal dust, will, in many mine-workings, raise a dense 

 cloud immediately in front of the flame, and the latter will thus be 

 fed as it advances. !Mt. Grallowav concludes, as the final result of 

 his experiments with coal dust, that the presence of fire-damp is 

 altogether unnecessary to bring abc'Ut a coal-mine explosion, but, 

 admitting that the result of c-ertain experiments may seem to favour 

 this conclusion, its realisation necessitates the fulfilment of con- 

 ditions which cannot but be very exceptional, and its acceptance is 

 certainly unnecessary to add to the formidable character of coal dust 

 as a source of danger and Em agent of destruction in mines. 



Whether an explosion originates with, or is chiefly caused by. the 

 production of a mixture of fire-damp with air in such proportions as 

 to be more or less rapidly and violently explosive ; whether the 

 originating cause be the reciprocal influence of a small proportion of 

 fire-damp and of coal dust (or dust of other descriptions of minerals 

 occurring in coal mines) co-existing in the air of a mine ; whether, 

 possibly, it simply originates with a m ix ture of very inflammable coal- 



