EXPLOSIVES 391 



fine coal-dust suspended in the air of a mine has long been 

 known to add to the danger of explosions when they occur from 

 presence of fire-damp, but it has only been recognised within 

 recent years that dust alone, diffused through air, forms an 

 explosive mixture through which flame is propagated, when 

 once started, with the violence characteristic of gas explosion. 



In France and in England large scale experiments have been 

 carried out within the last few years which have supplied very 

 valuable information. The English experiments at Altofts 

 have been provided for by the Mining Association of Great 

 Britain, and have been described by Professor Dixon in his 

 Presidential Address to the Chemical Society (London) in 1911 

 in the following passage : 



" An iron gallery 600 feet long and 7J feet in diameter was 

 constructed of cylindrical boilers bolted together. Inside a 

 tram-line on a concrete floor, with props and cross-timbers 

 placed at 9 feet intervals, made a travelling road, comparable 

 with the main haulage road of a mine. Shelves fastened to the 

 sides provided ledges for holding dust, and the flame of a blown- 

 out shot was reproduced by firing a stemmed gunpowder charge 

 from a cannon. Just before firing a current of air was drawn 

 into the main gallery by a fan placed at the end of a ' return ' 

 gallery. By this means a pure coal-dust explosion, extending 

 over several hundreds of feet, could be obtained, and the propa- 

 gation of the flame and pressure studied." 



The reports of the French Coal-Dust Experiments conducted 

 at the Lievin Experimental Station, near Lens, in 1907-10, 

 have been published in English by the Colliery Guardian. Ex- 

 periments were made similar to those described, and with similar 

 results. The principal gallery, constructed originally only 

 71 yards long, was extended till in 1910 it was 328 yards long, 

 with an internal height of 6 feet. 



The fact thus established is consistent with what is known of 

 other dust explosions, as in flour mills, where there can be no 

 question of the existence of inflammable gas in the atmosphere. 

 The initiation of the flame does not apparently depend on the 

 production of gas from the dust by a preliminary process of 

 distillation, and Dr. R. V. Wheeler, who has been in charge of 

 the laboratory at Altofts, has been able to show that an explo- 

 sion is propagated through a cloud of charcoal dust in air. 



With the object of limiting the risk of explosions in coal mines, 



