On the Influence of Coal-dust in Colliery Explosions. 



* E. A small air-fan driven by a steam turbine. 



F. The windlass. 



G. A grooved wheel for driving the fan inside the explosion 

 chamber by means of an endless cord that passes over a small grooved 

 pulley in the centre of the end of that chamber. 



H. The fire-damp pipe. 

 K. The steam pipe. 



When the vessel D is fall of water and raised to the point it 

 occupies in the drawing, its contents flow into the measuring vessel C, 

 and expel the air contained in it. The vessel D is then lowered until 

 its top is under the level of the bottom of the measuring cylinder, and 

 the water flows back out of the latter into the former ; and when the 

 upper end of the measuring cylinder is in communication with the 

 fire-damp pipe it fills with that gas. By raising the vessel D again to 

 the position occupied at first, the fire-damp can be expelled and 

 driven into the explosion chamber at a. 



Following are the various operations that require to be performed 

 before an experiment is made : — The explosion chamber is drawn 

 back and several sheets of paper are inserted between it and the 

 gallery, so as to form a diaphragm between them. They are then 

 bolted together, and the quantity of fire- damp required to produce the 

 most explosive mixture is forced into the explosion chamber from the 

 measuring cylinder, at the same time that a corresponding quantity of 

 air is allowed to flow out below. The lower opening is then plugged, 

 and the wheel Gr is revolved 100 times. Meanwhile the fan E can be 

 supplying heated air to the gallery through the channel which con- 

 nects them ; but in my later experiments I have not found that this 

 affects the result to an appreciable extent. The side which consti- 

 tutes the door of each section of the gallery is raised in succession, 

 and coal-dust is strewed on the floor to a thickness of §■ to \ inch ; 

 some is also laid on shelves, which are placed in sets of three, one 

 above the other, at distances varying from 10 to 20 feet apart. 



When the floor is made damp with water, so as to fix every particle 

 of dust that cannot be swept out with a brush, the flame of the fire- 

 damp explosion travels along the gallery to a distance of 12 feet on 

 the average. When the gallery contains coal-dust, on the other hand, 

 the explosion of the fire-damp raises it in a cloud, and the flame 

 appears to travel as far as the cloud contains more than a certain 

 minimum amount of dust, and then to die out for want of fuel. A 

 fair average distance is 70 feet, but it occasionally reaches 80 and 

 85 feet, and on one occasion it extended to 104 feet. The natural 

 supply of fire-damp is too limited to admit of the creation of an 

 atmosphere with an appreciable proportion of fire-damp in the interior 

 of the gallery, so that all the experiments have been made with pure 

 air hitherto ; and, further, as I have already mentioned, 1 do not find 



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