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



or horse-roads, and in these latter cases it so acts as a deterrent, that 

 such passages are rarely invaded by explosions. When this dust is 

 mostly shale, it may be dangerous, for some oily shales have yielded 

 much volatile matter. Thus, I have found some, on being roasted 

 on an iron plate, to turn from grey to black, and fall in weight 

 from twenty grains to ten, thus indicating as much as 50 per cent, of 

 volatile matter. 



Dust is found in pits (ist) on the floors of the road-ways, 

 (2nd) on the upper faces of the roof timbers and on natural ledges, 

 and lastly, on the vertical sides of the passages, the vertical props 

 and faces of the roof timbers, and even on the under horizontal faces 

 of such timbers. It facilitates the examination of pit-dust, to con- 

 sider the dust of these three indicated localities separately, for they 

 differ certainly much in constituents, especially in their proportions, in 

 physical condition, and perhaps in chemical too. That found on the 

 floors and lower parts of the sides has been called by Messrs. Atkinson 

 ('Explosions in Coal-mines,' by W. N. & J. Atkinson, H. M. 1. of 

 Mines. Longmans, 1886) ^Bottom' dust, and that on the upper faces 

 of timbers and ledges ' Upper'' dust; that on the upper vertical faces 

 and on the under side of roof timbers I propose to call ' Flocculent' 

 dust. It felts and hangs together with that peculiar ropy aspect seen 

 in ' soot,' and hence has been so called by miners. As regards 

 fineness, for example. Bottom dust is coarsest, Upper dust inter- 

 mediate, and Flocculent dust the finest. My examination points to 

 a similar conclusion as regards the percentage of dant. 



Dant is present in all pit-dust — bottom, upper, and flocculent ; in 

 the former to a small extent, in the two latter to a very large extent. 

 From the microscope I estimate its percentage to vary in bottom 

 dust between nothing and 50 per cent; in the upper and flocculent 

 dust between 40 and 70 per cent, or even 80 in the latter. 



Got as free from coal as possible, and piled in a little conical 

 mound on a slab of wood, it takes fire most readily when an ordinary 

 match is lighted and applied to it, burning steadily, with little smoke, 

 but with a strong smell (a smell quite characteristic of coal-mines), 

 through the entire heap, and with such energy that it scorches a deep 

 pit in the wooden slab on which it is burned. Even on a marble slab 

 it burns through the entire heap, giving the stone the appearance of 

 having been wetted. This is very significant, when the high con- 

 ductive power of the marble, compared with the wood, is considered. 

 On being burned on an iron plate, it begins to glow before the iron 

 plate is red, and burns on with a steady glow. The fumes it gives 

 off will not ignite. The mass changes from its ordinary deep black 

 to a pale fawn-coloured dust, and is reduced in weight from 20 to 



Naturalist, 



