98 Mr. F. A. Abel [April 28, 



from small cannon., so as to represent blown-out sliots in the effects 

 produced ; coal dust was placed upon the floor of the box, and one 

 shot was first fired against the air current which was passing at a 

 known velocity. The dust cloud thereby raised was carried along by 

 the current and a second shot was fired into it, and, in a large number 

 of experiments made with many different descriptions of dust, the 

 flame produced by the second shot was increased by that of inflamed 

 dust, a comparatively clear flame being sometimes produced, while in 

 other instances it was accompanied by a shower of sparks. The view 

 taken by Vital, Marreco, and others, regarding the action of coal- 

 dust in propagating flame in air free from fire-damp, is to the effect 

 that the first portions of dust acted upon by the inflamed gases of the 

 shot, liberate inflammable gas which mixes with the air, and is fired, 

 the non-volatile part of the coal being in part consumed and in part 

 deposited as a feeble coke. Some examination of coked deposits of dust 

 sent to Marreco subsequently by Mr. Galloway, confirmed the obser- 

 vations originally made by Faraday and Lyell, that the coal dust is in 

 part submitted to destructive distillation during the progress of the 

 flame through the dust-laden air. Marreco considers that, although a 

 proportion of the heat developed by the burning dust is absorbed by 

 the gasification of the coal-constituents, the heat of combustion of 

 these suffices to leave a margin for the carrying on of the action from 

 one particle of dust to another, provided these be in sufficiently 

 close proximity to each other. 



In the experiments made by the Chesterfield and Derbyshire 

 Institute of Engineers, in a very long gallery, results were obtained 

 very similar to those of Marreco and Morison, and it was also found 

 that a lengthening of a gas flame, which was placed in the gallery, 

 could be obtained by causing the current of air to carry with it thick 

 clouds of some descriptions of coal dust. 



Many instances are on record in this country and others of the 

 firing, with semi-explosive violence, of clouds of coal dust, produced 

 either in the open air, or in localities where no fire-damp could exist, 

 some portions of the mixture of dust and air having come into contact 

 with a flame or fire. Thus Marreco and Morison mention a case of 

 a considerable quantity of coal dust, which had been accidentally 

 thrown over some screens at a pit's mouth, flashing into flame as the 

 dust cloud came into contact with a neighbouring fire, and burning a 

 man very severely ; and another accident, which occurred in a stone- 

 drift, where it was believed that no gas could possibly be present. 

 A considerable body of rock was dislodged and coal dust raised 

 by the firing of a shot, the flame of which fired the air-and-dust 

 mixture, with very mischievous results. From 50,000 to 60,000 cubic 

 feet of fresh air were said to be passing through the drift per minute 

 when this accident occurred. 



There appear good grounds for believing that, provided coal dust 

 be sufficiently fine and thickly suspended in the air, and of a readily 

 inflammable nature, fire may travel to a considerable distance in the 



