774 EDITORIAL 



Only certain dusts, therefore, possess this property which Professor Abel 

 believed to be due to a contact, or catalytic, action upon the gas mixtures, 

 analogous to that manifested by finely divided platinum toward certain gases. 



Just how much influence shale dust could exert in this direction has not 

 been determined. It is possible that a mixture of firedamp and air, very close 

 to the lower limit of inflammability, but still not sufficiently rich in methane 

 to be ignited by a flame, might become ignited from the flame when a certain 

 amount of very fine, dry shale dust was stirred into it. But it is probable 

 that only a gas mixture which was very close to the limit of inflammability 

 could become ignited under these conditions. It is also to be remembered 

 that whatever influence of this sort the shale might have, would be possessed, 

 in a far greater degree, by even a very small amount of coal dust in the air. 

 In mines where there is always coal dust present in varying quantities, the pos- 

 sible activity of fine shale in facilitating an explosion should be negligible in 

 comparison to that of the coal dust. Furthermore, the heavier shale, or 

 earthy material, by adhering to the lighter coal dust, tends to keep it out of 

 the air. Finally, the phenomena of typical dust explosions in which the flame, 

 because of the great abundance or excess of combustible matter furnished 

 by the coal dust (even in non-gassy mines) , seeks the fresh intake air indicate 

 that these dust explosions are very different from what would be produced 

 by the ignition of mixtures of firedamp and air rendered explosive by the cata- 

 lytic action of the dust, but, instead, must be largely a matter of the rapid 

 combustion of the readfly inflammable hydrocarbons of the dust itself. 



Another objection which might be urged is that the shale and coal dusts 

 may become partially separated owing to their difference in specific gravity. 

 Ordinary air currents can pick up light coal dust more easily than denser 

 shale, or clay, particles. As a result, whatever dust might be stirred into the 

 air would be likely to contain a higher proportion of coal than that on the walls 

 or floors. But still there should be much less coal dust in the air, in absolute 

 mass, than if the shale treatment had not been applied, since the mud, because 

 of its adhesive properties, must hold down much fine coal dust which otherwise 

 might easily become floating in the air. However, when an explosion is once 

 started and under headway, it must sweep up nearly all the available dust, 

 coal and shale alike, and hence it would be the character of this mixed dust 

 which would determine the further progress of the explosion-. 



The foregoing discussion of suggestive preventive measures which were 

 the direct outcome of observational and experimental data have been extended 

 considerably upon theoretical grounds in order to bring out, in a more com- 

 prehensive manner, what advantages and disadvantages might be expected 

 to accompany the use of finely pulverized shale, clay, or other earthy material 

 in the mines. The discussion is intended merely to open up, in a preliminary 

 suggestive way, a field for investigation which appears to show some promise 

 of yielding results. 



