TRANSACTIONS OF SECTION B. 599 



•dust and pure air were not inflammable at ordinary pressure and temperature, it 

 would become so when a small proportion of firedamp was added ; and that the 

 coal-dust might fhus become the vehicle for conve_ying flame from one district of a 

 mine to another, alter it had been raised from the floor and mixed with the air of 

 the mine by some disturbing cause, such as a local explosion of firedamp or a 

 heavily charged blown-out shot. This view, that coal-dust and not firedamp plays 

 by far the most prominent part in great explosions, has been confirmed by all his 

 subseqiient observations, of which the following is a sketch : — 



1. In July 1875 he found that an air-current made black with fine coal-dust 

 was not ignited by the flame of a lamp, but that when the air contained a small 

 proportion of firedamp (insufficient to render it inflammable alone) it became 

 inflanmiable when the same proportion of coal-dust was added to it and burned 

 witli a red smoky flame that filled the apparatus. 



2. In December 1875 he made a quantitative experiment with the view of 

 ascertaining the proportion of firedamp required to produce the foregoing residts, 

 and he found that one per cent., or rather less, was sufficient to do so. He attributes 

 the satisfactory character of this residt, and of all the results of his later experi- 

 ments with coal-dust, to the fact that he has employed only wind-carried dust in 

 making them, and this dust has not parted with its finest particles like that which 

 is to be found under screens and in other exposed situations. 



3. In June, 1876, Messrs. Hall and Clark read a paper before the North of 

 England Institute of Mining Engineers, describing experiments which showed that 

 the flame of a blown-out shot was prolonged to a distance of fifty yards, when it 

 was directed in such a manner as to lick up coal-dust strewed on the floor of a 

 sloping gallery. During the same year the author had practical proof of the same 

 thing in a Welsh mine, in which two explosions of coal-dust, by which men were 

 burnt and injured, were originated in this way, but the explosions died out again 

 when they reached damp portions of the roadways. 



4. Professor Freire-Marecco, of the College of Physical Science, Newcastle-on- 

 Tyne, commenced a series of experiments in 1876, and has continued them on a 

 larger scale since then, and he has obtained results similar to the foregoing by means 

 of a special apparatus. 



5. In 1878 he made three sets of experiments M'ith different kinds of 

 apparatus : — 



a. In the first set, in which lighting gas was used instead of firedamp, and the 

 gas and air were carefully measured and the coal-dust weighed, it was sho^\^l that 

 2^ per cent, of gas mixed with air was rendered inflammable when coal-dust was 

 added ; 3 per cent, of gas made the mixtiu'e slightly explosive ; 4 per cent, made 

 it still more explosive ; and 6 per cent, produced a violent explosion. The total 

 quantity of gas and air mixture was little more than a cubic foot. 



b. Li the second set it was sho^vn that the return air of a mine containing 2 per 

 cent, of firedamp became inflammable when coal-dust was added to it. 



c. In the thii'd set the explosion of a mixtm-e of air and firedamp was made to 

 raise and ignite coal-dust scattered along the floor of an artificial gallery, 70 or 80 

 feet long, and 14 inches square inside. The flame of the firedamp explosion alone 

 was found to be 7 or 8 feet long ; the flame of coal-dust in pure air was 35 or 40 

 feet long ; and the flame of coal-dust in the return air employed in experiment a 

 was 80 or 90 feet long. The two sets of experiments b and c were described in the 

 ' Proceedings of the Royal Society,' March 1879, and the set a has been described 

 in a general way more recently. 



6. The great explosions of Risca, Seaham, and Penygi-aig Collieries took place 

 in the year 1880, and all of them appeared to be wrapped in the usual mystery 

 when viewed only from the firedamp standpoint. It was under these circum- 

 stances that the Home Secretary requested Professor Abel to inquire into the 

 causes of the Seaham explosion, and to ascertain if possible what influence, if any, 

 the coal-dust was likely to have had in promoting the explosion. Professor Abel 

 made experiments near Wigan, with an apparatus .similar to the one the author had 

 employed in July 1875, and obtained results similar in kind, but different in some 

 respects. He found that 2^- to 3i per cent, of firedamp was required to render a 



