1879.] Influence of Coal-dust in Colliery Explosions. 



419 



and 2 feet long, is filled with fire-damp, of which a certain measured 

 proportion is afterwards transferred to the interior of the cylinder A 

 through the india-rubber tube r n. This is done by admitting water 

 through an india-rubber pipe attached at the point 0. At the same 

 time as the gas is flowing in at the top of the cylinder A, air is allowed 

 to escape at the point b near its bottom by taking out a plug for that 

 purpose. The plug is put in immediately after the operation is com- 

 pleted. The amount of fire-damp employed is as near as may be '456 

 cubic foot. The cylinder E is refilled with fire-damp by shutting a 

 stop-cock at n, opening another at m, which is connected with the 

 fire-damp pipe by means of an india-rubber tube not shown in the 

 drawing, and lowering the water bucket below the level of the bottom 

 of the cylinder E. Before the fire-damp is admitted to the interior of 

 the cylinder A, a paper diaphragm is inserted between its lower end 

 and the ring to which it is hinged and screwed, so as to isolate it from 

 the gallery BC. The explosive mixture in the cylinder A is ignited 

 by the spark of a powerful magneto-electric machine which Messrs. 

 Cross Brothers, of Cardiff, most kindly lent to me for the purposes 

 of these experiments. The wires pass through the plug at b, and 

 are brought together just inside the cylinder. 



The method of forming an explosive mixture in the cylinder A, will 

 now be sufficiently plain, but I will repeat the description of the opera- 

 tions in regular order. When the cylinder is in the position shown 

 in fig. 4, several sheets of paper are laid over the opening in the top 

 of the gallery ; the cylinder is then raised to an upright position 

 and fastened by means of the screw. The plug b is opened and 

 fire-damp is made to flow through the pipe r n, displacing a corre- 

 sponding volume of air which escapes at b. As soon as the requisite 

 volume of gas has been obtained the cock r is shut and the plug b is 

 replaced. The driving wheel D is next made to revolve at the rate of 

 about eighty turns per minute ; twenty-five or thirty turns being 

 found quite sufficient to make a perfect mixture ; and, thereafter, a 

 spark from the magneto-electric machine causes the explosion. 



When there is no coal-dust in the gallery BC, the flame of the 

 fire-damp explosion does not extend further than from 7 to 9 feet 

 from the bottom of the cylinder A. It should be understood that the 

 valve at b is always closed just before the spark is passed. 



When the gallery contains coal-dust, on the other hand, scattered 

 along its floor, and lying on a few shelves, whose position will be 

 given immediately, and when it is filled with the return air of the 

 upcast shaft, the flame of the explosion traverses its whole length, 

 and shoots out into the air at the end of C, to distances varying from 

 from 4 to 15 feet beyond it. At first, it appeared to me that the 

 wooden gallery might be prolonged indefinitely with the same result ; 

 but on adding another pipe at the end of C, I was surprised to find 



