MancJusUr Memoirs^ Vol. Ivii. (1913), ^0. IS- 3 



hydrogen or hydrocarbon \-apour with oxj'gen or air, 

 oxidation .... is at once established and proceeds at a 

 rapidly accelerating rate, as the chemical activit}- is pro- 

 moted by the accumulating heat, so that the metal is 

 speedily raised to a temperature sufficiently high to bring 

 the surrounding gas mixture to the exploding point" 



These conclusions were apparently confirmed by an 

 experiment of Le Chatelier. Into a long vertical glass 

 tube (about 4fL x 3ins.) a mixture of air and gas is intro- 

 duced in such proportions that on lighting it at the top 

 the flame hovers about in the tube or slowly descends. 

 If magnesia dust is now dropped into the tube through a 

 Bunsen flame burning across the top of the tube, the flame 

 rapidly descends with the dust to the bottom. 



But in the Le Chatelier exf>eriment the dust is not 

 suspended in the gas-and-air current, but is falling under 

 the action of gravity through the mixture. A particle of 

 magnesia heated by the Bunsen flame would carr>' a cap 

 or small flare in its wake. If the gas mixture is non- 

 explosive this flare does not spread, but forms a luminous 

 tail to the falling particle ; but if the mixture \s just 

 explosive, the flame spreads sideways as the particle falls, 

 and thus forms an inverted cone of flame with the falling 

 particle at its apex. 



The importance of Abel's conclusion lies in the fact 

 that the addition of a finely divided non-combustible dust 

 has been adopted in some mines as a method of preventing 

 the explosion of coal-dust, and it has been urged that if 

 such non -combustible dusts may cause the explosion of 

 less than 3 per cent of firedamp, the remedy may really 

 be introducing another danger into mines. 



This aspect of Abel's work has naturally been con- 

 sidered by the Home Office Committee on Explosions 

 in Mines, who have carried out experiments both in the 



