WATTS : COAL-DUST AND EXPLOSIONS IN COAL-MINES. T49 



grains. Burned in a retort, it gives off no gas at the nozzle capable 

 of supporting flame, but is reduced in weight from 41 grains to 38 

 It leaves the retort as it entered it, a loose mass of dust. Dant once 

 thoroughly dry is not readily wetted but the water runs off, as 

 usually with very fine dust, in little spherules. It is much better wetted 

 by a moist atmosphere than by a direct application of water, and 

 hence in my letter to 'Nature' (12th Oct., 1886) I suggested that 

 keeping the ventilating air-current saturated with aqueous vapour 

 might be found the best practical means of rendering it innocuous.* 

 Dant clearly, therefore, is not itself dangerously explosive, yet is 

 admirably fitted to act the part that tinder used to do when it handed 

 on the spark from the flint and steel to the old-fashioned brimstone 

 match. Doubtless, in mine explosions wholly or chiefly due to 

 dust, this is the tinder^ as the shot flame or other initial cause is the 

 spai'k. 



Coal supplies a considerable portion of upper and flocculent 

 dust, and the great mass of ' bottom ' dust, along intake haulage- 

 ways, which are the usual tracks pursued by those explosions which 

 we believe to be essentially ' dust explosions.' 



When very fine, this coal-dust (got as pure as possible), piled in 

 a small heap, as was the dant, can be hghted with some little trouble 

 by a match, and burns at first somewhat fiercely and with considerable 

 smoke, then with less smoke and less energy, for it goes out before 

 consuming the entire heap, and only scorches the wooden slab to a 

 small extent. On the limestone slab it goes out before reaching the 

 bottom of the heap. Burned on an iron plate, it does not show a 

 glow till the plate is red, and then burns with small scintillations. 

 Its fumes take fire when a light is applied, and a pale blue flame, 

 occasionally tipped white, flickers over the heap. Its ash is reddish- 

 brown, and only weighs half a grain from 20 grains of dust. Burned 

 in a retort it gives off at first much smoke, which will not light. 

 Soon, however, the smoke lessens, and then it at once lights, and 

 burns with a long bright flame, which dwindles down after awhile 

 to a small pale blue flame, and very reluctantly goes out. On 

 opening the retort, the dust comes out a solid core of compact 

 whitish coke with a metallic lustre. 



Sucli coal-dust is manifestly capable of producing an explosion. 

 Under favourable conditions it can produce a considerable amount 

 of ordinary illuminating coal-gas, whose ])resence will convert tlie 



■* I am glad to see that Mr. Stratton (late manager of Seahani Colliery 1 has 

 made a preliminary trial of this method in a South Wales Colliery, with such 

 success that he is, at special request, pursuing this plan, witli the ol)ject of sub- 

 mitting a full report at the next meeting in this great coal-field (May 1887'!. 

 M.ny 1888. 



