772 EDITORIAL 



it has become completely dry. By adhering to the particles of fine coal, this 

 dust would be much less readily stirred into the air in everyday mining 

 operations. The mud, clay, shale, or whitewash coating upon the ribs and 

 props must bind the coal dust particles to the coal or timbers with sufficient 

 tenacity to prevent them from being swept up by the ordinary currents of 

 air passing through the entries. Because of greater adhesiveness, mud or 

 soft, clayey shale should be preferable to the more indurated slates, while 

 whitewash has some properties which make it superior to either. Perhaps a 

 mixture of lime and shale, or clay, would prove preferable to either of the 

 constituents used alone. 



Since the effects of sprinkling with this shale douche or mixture of earthy 

 material and whitewash last after the water has evaporated, it would not be 

 necessary to sprinkle the entries so often as when water alone is used, for 

 this property of non-combustible shale to diminish the inflammability of the 

 coal dust is not dependent upon the presence of a continuous supply of moisture 

 in the mines. Unlike sprinkling with water alone, if the dust is once made 

 comparatively harmless by the admixture of a very large amount of very fine 

 shale, or similar adhesive mineral matter, it remains so (even though the 

 mine be completely dried out) until an additional amount of coal dust has 

 accumulated, or the dusts in some way become partially separated. Whether 

 the dust be wet or dry becomes less important, though wetness constitutes, 

 of course, an additional safeguard. This manner of treatment implies a certain 

 amount of spraying with water, but a far less amount than the ordinary 

 sprinkling method. Hence the chief dangers of increased rock falls, and other 

 drawbacks of the common water method might be largely escaped. 



The treatment of the entry floors is simpler than that of the waUs. The 

 pavement may be sprinkled with the same preparation as the ribs and timbers, 

 but it would probably be better to grind the shale to a fine powder outside of 

 the mines, run it underground in the mine cars and spread the dust uniformly 

 over the pavement, throughout the entries. The coal dust on the floor would 

 then either be mixed with, or buried beneath, several times its weight of mineral 

 substance. If sufficient shale be spread along the entries and fairly tight 

 mine cars are used, the shale or earth on the pavement probably would not need 

 to be renewed for a considerable length of time. 



Whether shale dust on the entry floors alone, is competent to check a dust 

 explosion once under way, while the fine coal dust, unmixed with shale or 

 whitewash, is present upon the ribs and timbers, can only be told by trial 

 experiment. That an enormous amount of dust and fine particles of coal is 

 swept along the entries during an explosion was strongly brought out by an 

 inspection of the coal ribs in these exploded mines. Very generally through- 

 out these mines, except where the mechanical force of the explosion was greatly 

 reduced, the exposed corners and protuberances of the coal were rounded and 

 often highly polished on exposures facing the source of the explosion, while 



