420 Influence of Coal-dust in Colliery Explosions. [Mar. 13, 



that I could not, by any possibility, get the flame to travel more than 

 one-half or two-thirds of the former distance, and I came to the 

 conclusion that the initial impulse, which raises the coal-dust, is 

 insufficient to overcome the resistance under the altered conditions. 

 Again, I had 60 feet, of nearly air-tight pipe prepared, thinking 

 thereby to prevent the energy of the wave created by the fire-damp 

 explosion from being dissipated ; but here, once more, I found that 

 it was impossible to get the flame to travel to a distance of more than 

 30 or 40 feet from the origin, and in this case I concluded that the 

 expanded part of the wave extinguished the flame of the coal-dust. 

 The best results were obtained when the wooden pipes had open seams 

 along the junction of the boards of which they are formed. 



At the beginning of the present month (March, 1879), Professor 

 Gr. G. Stokes, F.R.S., communicated to me the suggestion that if a 

 weak solution of chloride of calcium were used for watering the road- 

 ways of mines, instead of ordinary water, the deliquescent salt would 

 tend to retard evaporation, and a smaller quantity of water would 

 serve the purpose of keeping the workings damp. Accordingly, I 

 have begun an experiment with such a solution in a dry mine, but 

 it is not yet sufficiently advanced to enable me to state any results in 

 the present paper. 



The temperature of the air current passing along the gallery varied 

 from 74° F. near the explosion-cylinder to 60° at the end C. The 

 wooden shelves spoken of above were in sets of three (one above the 

 other at equal distances) the shelves themselves being about 6 inches 

 broad. One set was placed at each of the points x , fig. 6 ; and a 

 brick was placed so as to obstruct the passage below the lowest shelf 

 of the first, third, and fourth sets for the purpose of causing the force 

 of the explosion to exert itself more powerfully in sweeping the dust 

 off the shelves and mixing it with the air. 



The arrangements whereby pure air, or pure air and fire-damp, 

 can be employed, were only completed before the weather became 

 unsuitable for continuing the experiments, which, I need hardly say, 

 are made in the open air. I obtained sufficient results, however, to 

 show that the absence of even the small proportion of fire-damp 

 -contained in the return air of Llwynypia Colliery, makes a great 

 difference in the force of the explosion and the distance to which the 

 flame will travel along the gallery. I found, also, that when two 

 per cent, of fire-damp was added to the current of pure air entering 

 the fan F, even better results were obtained than with the return air 

 of the mine. 



Although this apparatus appears to be on too small a scale to 

 solve the coal-dust question unequivocally, I think the results obtained 

 with it are sufficiently conclusive to enable us to affirm, that a fire- 

 damp explosion, occurring in a dry coal mine, is liable to be in- 



