1876.] of Coal-dust in Colliery Explosions. 359 



extending over a distance of 322 yards of the workings, pointing to the 

 presence of a large body of inflammable matter ; and yet the amount of 

 damage done was insignificant. The traces on the props undoubtedly 

 indicated the direction in which the air was travelling when the coked 

 coal-dust was deposited; and I could not satisfactorily reconcile the 

 various directions indicated in this way, except on the supposition that 

 the inner end of the level (O, fig. 2) had been the origin of the explosion; 



that in the level itself and in the two places (O', O") branching from it to 

 the dip (the only branches in which the traces were distinct), the coke 

 was deposited during the retrograde movement of the air; and that in the 

 places leading from the outer end of the level (0'") it was deposited 

 during its outward movement. 



If we supposed, for example, that all the coke had been deposited while 

 the air was moving away from the origin of explosion, it would be neces- 

 sary to assume three distinct origins, one in each of the dip places at 

 points where no gas could possibly accumulate (0', O"), and one at the 

 outer end of the level (O"'), where there was no cavity in the roof, and 

 where the whole of the ventilation was passing. 



Every circumstance tended to show that some explosive gas had accu- 

 mulated at the inner end of the level, where there was no ventilating cur- 

 rent; that this gas had ignited at one of the naked lights, raising a cloud 

 of dust along the level by its explosion, and that there had been sufficient 

 firedamp in the air occupying the level to form a weak explosive mixture 

 when the coal-dust was added. 



There could be no doubt whatever that the whole of the air in the 

 level contained some firedamp, so tbat it became a matter of importance 

 to ascertain the smallest quantity required to make air explosive when 

 coal-dust is added ; and with this object in view I made further experi- 

 ments on the 13th of December. 



The apparatus at Llwynypia Colliery was altered somewhat. Kg. 3 



