Manchester Memoirs, Vol Ivii, (191 3), No. 15- 9 



So long a wire has, of course, a much greater surface than 

 the shorter wire, and consequently a much larger pro- 

 portion of the gas will burn on the wire before it reaches 

 the ignition point of the mixture. So rapidly is the 

 composition of the mixture reduced that a spark passed 

 several seconds later would not explode the gas. 



Experiments were tried to find exactly how long was 

 necessary for the gas to be treated in order to just bring 

 it to a non-explosive point. The platinum wire was 

 heated by a current sufficient to bring it to very dull red- 

 ness in air. When heated in an 8 % mixture it glowed 

 brightly, and when a spark was passed eight seconds after 

 the heating current had been turned on, it was found that 

 the gas would not explode. When the spark was passed 

 seven seconds after the heating current had been turned 

 on, a feeble explosion resulted. 



A sample of 8 % coal gas taken at a different time 

 was reduced to a non-explosive point in seven seconds 

 but not in six seconds. 



On the other hand, a sample of 6% coal-gas which 

 was not capable of being exploded by a spark was tried 

 in order to see whether by any heating of the platinum 

 wire it could be made to explode. 



It was found that no explosion was produced either 

 by gradually heating the wire as in previous experiments 

 or by suddenly heating it, even to a white heat. The gas 

 could not be exploded by a spark passed immediately 

 after the current had been switched on. 



In this experiment the ideal conditions demanded by 

 Abel have been reproduced. The platinum surface, to 

 represent the dust has been heated, combustion takes 

 place on its surface, thereby intensifying the heat, but it 

 does not bring about (as Abel said) the general ignition 

 of the gas greatly diluted with air. 



