1909] on Means of Saving Life in Coal Blines. 477 



it is impossible to suppose were all filled with gas in an explosive con- 

 dition. Thus at Seaham, the explosion ran for four miles. 



2, The fact that big explosions do not occur except in drj and 

 dusty mines. 



o. The fact that explosions always run along intake airways 

 and main haulage roads, where fine dust abounds, raised by the 

 wagons carrying the coal, which is rendered very dry by the great 

 quantities of dry air sent into the mine. 



4. And lastly, the presence of after-damp, of which I will say more 

 by-and-by. 



It may now be of interest to show on a small scale the inflamma- 

 biUty of certain kinds of fine dust. 



Lycopodium, the seed of a fern, is very inflammable, and was 

 once used to produce lightning on the stage. 



[Experiment.] 



Magnesium powder is well known. Most of the company have 

 probably undergone the process of being photographed after some 

 public dinner by the flash-lamp. I will put only a little here as the 

 light is very blinding. 



[Experiment.] 



I can even show here by the simple expedient of blowing a little 

 exceedingly fine coal-dust into a flame, that the dust is inflammable. 



[Experiment.] 



But a much better way is that arranged by Professor Bedson, 

 which he is kind enough to manipulate for us. A small charge of 

 fine dust is puffed from a compressed air reservoir into this globe 

 and is ignited by the coil of platinum. 



[Experiment.] 



The interest of this apparatus is that by its use Professor Bedson 

 has been enabled to show that different sorts of coal-dust have very 

 different degrees of inflammability. 



Dust when ignited can be made to traverse a gallery. A wave of 

 air disturbance precedes the ignition stirring up the dust. Then 

 follows a long lick of flame, which as it proceeds acquires greater and 

 greater velocity until at last after a long run it acquires explosive 

 violence. This little model gallery contains a layer of lycopodium 

 powder, which is ignited by a puff of flame sent into it, and you see 

 the flame gently rush along and come out at the end. 



[Experiment.] 



