1876.] of Coal-dust in Colliery Explosions. 367 



and temperature, when charged with tine dry coal-dust, such as that which 

 is to be found on the roadways in dry coal-mines. 



It seems, therefore, only reasonable to conclude that an explosion, 

 originated in any way whatever, in a mine of this class, may extend itself 

 to remote parts of the workings where the presence of firedamp was quite 

 unsuspected. 



It is by no means so uncommon as might be imagined to find the air 

 at the face of the workings and in the return air-courses of what are 

 considered to be well-ventilated mines showing a cap at least J inch high 

 on the small oil-flame. I refer to my own observations in mines abound- 

 ing in dry coal-dust, and reported to be free from gas, because no inflam- 

 mable accumulation was known to exist in them at the time. In these 

 cases the firedamp appears to be given off quietly at a uniform rate along 

 the face of the coal, but nowhere in such quantity as to render the atmo- 

 sphere locally inflammable. To give some notion of the volume of gas 

 given off in this way, I need only mention that, in one instance, I found 

 an air-current, whose volume amounted to 34,000 cubic feet per minute, 

 showing a cap \ inch high. Taking this case as an example, we may 

 suppose the amount of air to be doubled, so that where a cap \ inch 

 high was to be found formerly there is now no trace of gas. Then we 

 know that, so long as the coal-dust remains undisturbed, naked lights 

 might be used with perfect safety ; but let it once be raised and ignited 

 by a small local explosion of firedamp, or by a shot such as that which 

 caused the explosion in the Campagnac Colliery, and the final results may 

 be of the most serious description. In this way some of the great ex- 

 plosions which have occurred in mines supposed to be almost, if not 

 quite, free from explosive gas may perhaps be accounted for. 



The explosion in the Campagnac Colliery might possibly have been 

 partly due to the presence of a small proportion of firedamp in the atmo- 

 sphere of the working-place in which it occurred. That place had been 

 driven in coal to a distance of 25 metres beyond the ventilating-current 

 of the district, and was ventilated only by an eddy which passed inwards 

 along the floor and returned along the roof ; and, although no firedamp 

 had been found in it, the workmen were provided with a safety-lamp 

 with which they were expected to make a careful examination before 

 igniting a shot. This precaution was considered necessary, since slight 

 explosions had taken place in other parts of the same mine. Lastly, the 

 working-place was quite level, so that it offered no opportunity for an 

 accumulation of explosive gas to be formed in it. 



The most striking circumstance, however, connected with this explo- 

 sion is that, although it raised a dense cloud of coal-dust along the gal- 

 lery which formed the prolongation of the place in which it occurred, to 

 a distance of from 130 to 150 metres, the flames do not appear to 

 have extended more than 7 metres beyond the point at which they first, 

 encountered the ventilating-current. 



