EDITORIAL 773 



nearly always angular and duU on the corresponding exposures facing from the 

 blast. This rounding indicated much abrasion and wear, and resembled 

 somewhat the familiar polishing of bowlders and pebbles by the sand blasts 

 in arid regions. As this smoothing of corners and burnishing of exposed 

 surfaces was all accomplished in the very short length of time which the explo- 

 sion occupied in traveling through a given section of an entry, the mass of 

 dust and particles of coal carried along by the blast must have been very great. 

 If such a mass of fine, non-combustible shale dust be swept up from the pave- 

 ment of an entry which has previously been thickly covered with this material, 

 it is possible that the whole explosion might be stopped by this influence 

 alone. 



Because the principles of the shale treatment apply to either wet or dry 

 dusts, it would seem that, by this means, the chief danger of over-ventilation 

 during the cold season of the year might be greatly lessened, if not eliminated. 

 With the coal dust thus treated, the gas in the mines could then safely be 

 removed by the vigorous ventilation which is required to remove the fire- 

 damp and to supply the miners with fresh air. 



The introduction of shale, clay, or whitewash should be free from any 

 injurious effects, either upon the mine or the miners at work. As these sub- 

 stances do not begrime men to anything like the degree that coal dust does, 

 the conditions in the workings should be improved rather than otherwise, 

 from the miners' standpoint. Whitewash, by rapidly absorbing carbon dioxide 

 from the mine air, should have a favorable influence upon the hygienic con- 

 ditions of a mine. While sprinkling a mine continually with water weakens 

 the roof and increases the number of rock falls, whitewashed walls, by greatly 

 enhancing the illumination of an entry, make it easier to detect dangerous con- 

 ditions at the roof. 



The introduction of pulverized shale, or other earthy material into a mine, 

 thus increasing the quantity of fine dust in the workings, may possibly seem to 

 be increasing one source of danger while reducing another. The experiments 

 of Sir Frederick Abel have shown that certain mixtures of methane and air 

 which passed a naked flame without any symptom of ignition were inflamed 

 when particles of fine, light, non-combustible powder, such as calcined mag- 

 nesia, were suspended in the gas.^ 



While these gas mixtures were such as could not be exploded by a naked 

 flame they were, nevertheless, not far below the explosive limit. Professor 

 Abel further qualified the statement of his conclusions in this way: "The power 

 of favoring the ignition of mixtures of firedamp and air was not exhibited by 

 some other powders similar in fineness to the latter, but different in structure 

 and density from this and one or two other non-combustible dusts which may 

 be called active; even different samples of magnesia, differing somewhat in 

 likeness from each other, appeared to possess the activity in different degree." 



' Sir Frederick Abel, Proc. Roy. Inst., X (1882), 88-113. 



