EDITORIAL 771 



The chief precaution which has been taken against dust explosions in the 

 past has been to sprinkle the entries with water, but sprinkling the mine with 

 ordinary water is effective only so long as the dust is kept in a moist condition, 

 which is not long in the winter time. This method seems to have been ineffect- 

 ive in these exploded mines because the sprinkling did not reach the various 

 points in the mines until long after the water of the previous wetting had 

 evaporated and the dust become dry. Water, in order to constitute any real 

 safeguard by itself, must be sprayed over all parts of a mine at short intervals. 

 This involves much labor, and, in time, expense. It also has the great dis- 

 advantage of weakening the roof in certain mines and increasing the likelihood 

 of rock falls which, after all, cause more fatalities than explosions. Turn- 

 ing exhaust steam into the intake air, while it helps to raise the temperature 

 of the air and supply it with moisture, also favors rock falls, and in addition 

 is said to rot the mine timbers. 



A suggestion which has been made is to sprinkle with a solution of calcium 

 chloride instead of pure water. Calcium chloride has such a strong affinity 

 for water that it absorbs moisture rapidly from the air, and a solution of it 

 could never be evaporated dry in ordinary atmospheric air. Dust, wet with 

 a strong solution of calcium chloride should remain damp for a long time, 

 even though the circulating air were in the proper condition to exert a strong 

 drying influence upon the mine. Treated in this way, the dust might be 

 kept so thoroughly dampened that the chances of a dust explosion would be 

 greatly reduced. The expense of using this solution need not be very great, 

 for calcium chloride can be cheaply manufactured. However, with the mine 

 wet with a strong solution of calcium chloride, it is possible that the miners, 

 by constantly coming in contact with it, might suffer both from the rotting 

 of their clothing and possibly an injurious effect upon their health. 



Arising from the studies of the dust at Monongah are the suggestions that 

 the explosibility of coal dust may be much reduced by mixing with it finely 

 pulverized shale. One of the most obvious ways to mix this non-combustible 

 matter with the coal dust on the ribs and timbers of a mine is to stir finely 

 ground shale, or similar earthy material, into the water with which the mine 

 is sprinkled. It is clear that means can be devised by which it will be possible 

 to keep shale, mud, or lime constantly stirred up in the water during the opera- 

 tion of sprinkling. When the water dries it must leave behind the mineral 

 matter held in suspension and thus form a coating upon the walls. If this 

 operation be frequently repeated, the amount of non-combustible impurity 

 mixed with, and adherent to, the dust on the ribs must steadily increase and 

 render the coal dust less and less capable of feeding and carrying an explosion 

 flame, so long as the dusts remain mixed. 



One of the greatest possible advantages which may be claimed for the use 

 of shale, earth, or lime, in the water, is based upon the property of mud to 

 adhere to that with which it comes in contact, and to hold together, even after 



