EDITORIAL 767 



from the loss of the volatile matter this accounts for but a small part of the 

 great increase in the ash from these two dusts over that in the original coal. 

 The difference is clearly due to the admixture of finely powdered shale swept 

 up by the explosion. Small fragments of shale were readily recognized in the 

 ash residue after the carbon had all been burned out. A fact which I believe 

 to be of great significance is that the uncharred dust contains nearly twice as 

 much ash {shale dust) as the charred dusi. These dusts came from the opposite 

 sides of the same identical props in a room into which the flames penetrated. 

 Both dusts must have been subject to the explosion and yet they are very 

 different in composition, the difference everywhere in the room depending 

 upon which side of the prop the dust was located, the explosion having served 

 as an admirable sorter. Now the explosion did not originate in this room, 

 but advanced into it from the entry, and the outby sides of the props against 

 which the dust was forcibly driven by the explosion are coated with dust 

 containing nearly twice as much shale dust as is contained in the charred dust 

 on the inby exposures of the props. The other and most significant difference 

 is that the dust (on outby exposures) containing 28 per cent of ash and shale is 

 not charred while the dust (on inby exposures) which contains only 15 per cent 

 of ash and shale is charred and has lost much more of its volatile hydrocarbons. 



The differences in the charring of the dust and in the proportion of fine 

 shale in the dust, I beheve, are interrelated, one being the result of the other. 

 The explanation, I think, is this: The dust is driven against the outby sides 

 of a prop with much force but not with equal force, the shale particles by reason 

 of their density being driven against it with greater force and hence more 

 likely to stick. The portion which adheres on the outby side of the prop 

 therefore contains more shale dust and less coal dust than an average sample. 

 In the lee of the prop there is a reduced pressure, and an eddying current 

 laps around against the inby side and permits more quiet adhesion. Now 

 the specific gravity of this coal is i . 30 while that of average shale is about 

 2 . 60, which is just twice that of the coal. The coal dust is also likely to be 

 finer than the particles of shale. Hence much of the heavier shale particles 

 will be carried on past the post, while the weaker eddying current which touches 

 the lee side will contain a much higher percentage of the lighter coal and less 

 of the heavier shale. This explains the difference in the percentage of ash 

 brought out so strikingly by the analyses. 



The high percentage of shale in the dust by diluting the combustible dust 

 and absorbing much of the heat necessary to inflame it has had such a dampen- 

 ing effect upon the combustion that the coal dust which was driven against 

 the props directly was not charred. But in the lee of the props where the 

 proportion of non-inflammable shale has been much reduced and the expulsion 

 of the volatfle combustibles is favored by the partial relief of pressure and the 

 slower current, the dust yields up to the flame much more of its inflammable 

 gases and becomes charred or even coked. 



