414 



Mr. W. Galloway on the 



[Mar. 13, 



cent, of fire-damp in the return air, the slightest puff: of a local fire- 

 damp explosion, or of a blown-out shot, will raise sufficient dust to 

 increase the amount of inflammable matter a hundredfold, and produce 

 all the phenomena that have been observed in this and similar cases. 

 Locked safety lamps were used, and shots were fired. The cause of 

 this explosion, like that of the preceding ones, will in all probability 

 never be ascertained. 



When smoke and soot are produced ; or dust is ejected from the 

 shafts ; or the coal, stone, and timber have a charred appearance, due 

 to a deposit of coked coal-dust on their surface ; or, lastly, when large 

 superficies of the sides of the galleries are found to be on fire imme- 

 diately after the event, we may safely conclude that coal-dust has 

 played an important, if not a predominant, part in the explosion. The 

 manner in which coal-dust operates in setting fire to coal and timber 

 is probably as follows : — The air is travelling rapidly in one direction 

 along a gallery, throwing a continuous shower of dust, small pieces 

 of coal, &c, against all surfaces that deflect it or obstruct its course ; 

 at the instant the flame traverses it, however, the coal-dust is melted ; 

 it then assumes the properties of flaming pitch, adheres to the surfaces, 

 against which it is thrown, and rapidly accumulates until it forms a 

 crust of greater or less thickness, according to the length of time the 

 air continues to travel in the same direction. If it is thick enough to 

 retain its high temperature, and is supplied with fresh air immediately, 

 it continues to burn, and the flame soon communicates itself to the 

 body of the coal or timber ; but if it is thin, or if the surrounding 

 atmosphere cannot support combustion, it becomes extinguished. In 

 the second case, the surface covered with the crust or layer of coke 

 is vulgarly said to be charred. 



During the course of the past year I have been enabled to make a 

 considerable number of experiments with mixtures of coal-dust, air,, 

 and fire-damp ; thanks to the liberality of the Lords of the Committee 

 of Council on Education, who acted upon the recommendation of the 

 Government Grant Committee in affording me pecuniary aid ; and 

 thanks also to the kind co-operation of Mr. Archibald Hood, managing 

 director of Llwynypia Colliery, and his two sons, Messrs. Robert and 

 William Hood, whose assistance has been quite invaluable to me. The 

 two experiments I propose now to describe were made at Llwynypia 

 Colliery with the coal-dust and fire-damp, whose analyses are given 

 at pp. 357 and 358 of the " Proceedings," No. 168, 1876. 



In order to test the truth of the hypothesis that the return air of a 

 mine in which a considerable amount of fire-damp is emitted by the 

 coal may be rendered inflammable by the addition of coal-dust, I had 

 an apparatus constructed at Llwynypia Colliery, and placed close to 

 the ventilating fan in such a position that a current of the return air 

 from the upcast shaft could be made to pass through it at pleasure. 



