1876.] of Coal-dust in Colliery Explosions. 355 



remarkable when it is remembered that a mixture of air with several other 

 combustible solids in a finely divided state is explosive at ordinary pres- 

 sure and temperature, and that some serious explosions have been caused 

 by the accidental ignition of very fine dry flour suspended in the air in 

 confined spaces. 



This subject has attracted more attention in France. In the first 

 Number of the ' Annales des Mines ' for the year 1875 there are some 

 notes referring to it, together with a paper by M. Vital, Ingenieur des 

 Mines. M. Vital describes, in a very minute manner, all the phenomena 

 produced by an explosion in the Campagnac colliery on the 2nd of No- 

 vember, 1874. A shot, which blew out the tamping, was fired in one of 

 the working-places, in a seam of bituminous coal, and was accompanied 

 by an explosion which burnt three men so seriously that they died within 

 a week. No firedamp had been detected in this place at any time ; but 

 as the floor was covered with very fine, dry coal-dust, and as the shot was 

 fired at the bottom of the face, and would consequently raise a cloud of 

 dust, it was concluded that nothing but the instantaneous combustion of 

 coal-dust, under the influence of the shot, could account for the accident. 



The writer then describes the nature of the coal-dust, both in regard 

 to the size of the particles and their chemical composition ; and afterwards 

 he gives an account of some experiments conducted by him in the E-odez 

 laboratory, for the purpose of ascertaining to what extent a flame resem- 

 bling that of a shot is lengthened when suddenly lanced into an atmo- 

 sphere consisting of air with fine coal-dust suspended in it. In con- 

 cluding, he says : — " Very fine coal-dust is a cause of danger in dry 

 working-places in which shots are fired; in well-ventilated workings it 

 may of itself alone give rise to disasters; in workings in which firedamp 

 exists it increases the chances of explosion ; and when an accident of this 

 kind does occur, it aggravates the consequences." 



I had carefully thought over this subject for a considerable time before 

 I had seen M. Vital's paper, and had come to a conclusion somewhat 

 different from his. It was this: that air mixed with certain propor- 

 tions of firedamp and dry coal-dust would be explosive at ordinary pres- 

 sure and temperature, although the presence of the same proportion of 

 one of the combustible ingredients, or the other, alone, might be insuffi- 

 cient to confer this property on the mixture. I derived this opinion 



increasing gradually to a certain distance as we neared the place of ignition. This 

 deposit was, in some parts, half an inch, and in others almost an inch thick ; it ad- 

 hered together in a friable coked state ; when examined with the glass it presented the 

 fused round form of burnt coal-dust, and when examined chemically, and compared 

 with the coal itself reduced to powder, was found deprived of the greater portion of 

 the bitumen, and in some cases entirely destitute of it. There is every reason to 

 believe that much coal-gas was made from this dust in the very air itself of the mine 

 by the flame of the firedamp, which raised and swept it along ; and much of the 

 carbon of this dust remained unburnt only for want of air." 



