1882.] On the Influence of Coal-dust in Colliery Explosions. 445 



being projected beyond the end of the gallery, it occasionally assumed 

 large proportions, and the flame, which afterwards shot into it, also 

 became enlarged nntil it appeared to have a diameter varying from 

 5 to 9 feet on different occasions. It then emitted a load roaring sound 

 and exhibited all the phenomena of incipient explosive combustion. 



Crusts of coked coal-dust were found adhering to the edges of the 

 transverse shelves farthest from the explosion chamber, and their 

 opposite edges were covered with a thin deposit of soot and dust, 

 which had a velvety feeling when touched. These circumstances 

 seem entirely to corroborate the hypothesis first proposed in No. I 

 paper, in connection with Llan Colliery explosion, and afterwards 

 revived in No. Ill paper, in connexion with Penygraig Colliery 

 explosion, to the effect that the crusts of coked coal-dust are, as a 

 rule, deposited during the retrograde movement of the air, that is to 

 say, while it is travelling backivards towards the origin of the explosion. 



The results stated in the foregoing pages strengthen and confirm 

 the opinions I have expressed in each of the three preceding papers 

 on the same question, as to the manner in which the flame of an 

 explosion is originated and propagated in a dry and dusty mine. The 

 experiments described in the first paper seemed to show that a 

 mixture of air and coal-dust is not inflammable at ordinary pressure 

 and temperature without the presence of a small proportion of fire- 

 damp ; but those described in this place show conclusively, I think, 

 that fire-damp is altogether unnecessary, when the scale on which the 

 experiments are made is large enough, and when the fineness and dry- 

 ness of the dust are unquestionable. It may be objected that, 

 although the particular kind of dust I have generally employed may 

 form an explosive mixture with pure air, it does not follow that other 

 kinds of coal-dust will do the same, even under the very same con- 

 ditions as to fineness and dryness.. I am inclined to' think, however, 

 that the objection has very little real! importance as far as the general 

 question of colliery explosions is concerned. Possibly the dust pro- 

 duced in mines in which very dry or an chracitic qualities of coal are 

 worked might not behave in the manner indicated. But the number 

 of mines of this class now being worked in this country is far too 

 small, as compared with the whole, to be of any practical account. 



I may add., in concluding, that the views advocated in these papers, 

 or similar ones, have been held for many years by a few eminent 

 French engineers, including MM. Verpilleux, Vital, and others ; and 

 they now appear to be making rapid progress amongst the practical 

 mining men of our own country, who, judging by the reports that 

 have reached me from many sides, are urgently desirous of obtaining 

 as much information on the subject as they possibly can. 



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