410 



Mr. W. Galloway on the 



[Mar. 13, 



II. " On the Influence of Coal-dust in Colliery Explosions." No. 

 2. By W. Galloway. Communicated by Robert H. 

 Scott, F.R.S., Secretary to the Council of the Meteorologi- 

 cal Office. Received February 27, 1879. 



In the former communication on this subject, which I had the 

 honour of submitting to the Fellows ( "Proc. Roy. Soc," vol. xxiv, 

 p. 354), some experiments were described which showed that a 

 mixture of air and coal-dust of a certain known chemical composition 

 was not inflammable at ordinary pressure and temperature ; and that, 

 when 0"892 per cent, of fire-damp (by volume), or a greater propor- 

 tion, was added to the same mixture, it became inflammable and 

 burned freely with a red smoky flame. The general conclusion to 

 which the second result pointed was also stated in the same place to 

 be, that, an explosion originated in any way whatever in a dry and 

 dusty mine, may extend itself to remote parts of the workings, where 

 the presence of fire-damp was quite unsuspected. 



The wetness or dryness of the workings of a mine depends, other 

 things being equal, on the temperature of the strata in which they are 

 situated : for it is obvious that if, on the one hand, the temperature 

 of the mine is lower than the dew-point of the air at the surface, the 

 ventilating current will deposit moisture as it becomes cooled in pass- 

 ing through the workings ; and if, on the other hand, the temperature 

 of the mine is higher than the dew-point of the ah at the surface, the 

 ventilating current will absorb moisture and tend to produce a state of 

 dryness. It is well known, however, that the temperature of the 

 strata in the Coal Measures of this country increases at the rate of 

 about 1° F. for every 60 feet of additional depth below the surface, 

 and, therefore, from what precedes, it is evident that the comparative 

 wetness or dryness of a mine depends on its depth. 



As far as my own observations are concerned, I have found that 

 coal mines, shallower than 400 feet, are damp or wet, and those 

 deeper than 700 feet are dry and dusty : between these two points, 

 also, there appears to be a kind of debateable ground in which wetness 

 or dryness depends, for the time being, on the coldness or warmness 

 of the air entering the mine at the surface. 



In all dry coal mines the coal-dust lying on the floor of the road- 

 ways rises in clouds and fills the air when it is disturbed by the 

 passage of men, horses, small waggons, &c. ; a sudden puff of air, 

 therefore, such as that produced by a local explosion of fire-damp, or 

 by a shot blowing out its tamping, must necessarily produce the same 

 effect in a greater or less degree according to its intensity. The 

 mixture of coal-dust and air, formed by the action of either the fire- 



