568 



NATURE 



[February 22, 191 2 



SOME PHASES OF THE COAI^DUST 

 QUESTION.' 

 TJP to the year 1875 all great colliery explosions in this 

 ^^ country were attributed to the accidental ignition of 

 a large volume of firedamp that had either previously 

 existed in an abandoned empty space, or goaf (like that 

 which admittedly caused the Whitehaven explosion in May 

 1910), or was supposed to have burst suddenly into the 

 workings and filled them with inflammable gas. In the 

 absence of a goaf, and when, for some reason or other, the 

 occurrence of an " outburst of gas " was not assumed, the 

 cause of the explosion was described as a mystery. 



In 1845 Faraday and Lyell directed attention to the 

 presence of crusts of coked coal-dust and to the evidences 

 of intense heat which they had observed in the workings 

 of Haswell Colliery after an explosion, which they, no 

 doubt correctly, assumed had been caused by the accidental 

 ignition of a large quantity of firedamp" in the goaf. 

 Following up that assumption, they remarked that " there 

 was every reason to believe that much coal-gas was made 

 from this dust in the very air itself of the mine by the 

 flame of the firedamp, which raised and swept it along." 



These words indicate clearly, I think, what was in their 

 minds, namely, that the participation of the coal-dust was 

 an important, but by no means an essential, incident in the 

 firedamp explosion. 



During the fifteen years preceding 1875 some French 

 engineers expressed the opinion that coal-dust must have 

 greatly lengthened the flame of certain small explosions of 

 firedamp and blasting shots, and aggravated the con- 

 sequences to a corresponding extent ; and one of them, M. 

 Verpilleux (whom, however, none of his contemporaries 

 seemed disposed to follow), went so far as to compare, in 

 relative importance, the initial flame with that of the 

 priming, and the coal-dust flame with that of the discharge, 

 of a gun. 



I had been seeking for a rational explanation of great 

 explosions for some years before I came to South Wales 

 as assistant inspector on mines. Before that time I had 

 had much experience in investigating the causes of small 

 firedamp explosions in damp and wet mines in Scotland, 

 but of no explosions of any kind in dry and dustv mines. 

 Accordingly, when I found that all the great explosions in 

 this district had occurred in mines of the latter, and none 

 of those of the former class, I began to associate them 

 with the presence of coal-dust. Acting under this 

 impression, I made experiments in the summer (July 3) of 

 1875 with a mixture of coal-dust and air, which was made 

 to flow through the small wooden apparatus described in mv 

 first paper on coal-dust referred to hereafter. I found 

 that when a small proportion of firedamp, less than that 

 contained in the return airways of practicallv everv fierv 

 mine, was added, the resulting mixture could be ignited bv 

 means of a naked light, and continued to burn with a 

 dark yellow, smoky flame so long as coal-dust and fire- 

 damp were supplied to the current. This discovery proved 

 to my entire satisfaction that coal-dust, although consist- 

 ing of solid particles, played exactly the same part as a 

 combustible gas when disseminated in the air — could, in 

 fact, be substituted for firedamp, and did not require the 

 extraneous heat of a firedamp flame, as imagined bv 

 Faraday and Lyell, "to distil coal-gas from it." So far 

 as I was personally concerned, the question was solved 

 then and there ; that is to say, I had no longer a shadow 

 of doubt that coal-dust played the principal, and firedamp 

 only a subordinate, part in all great explosions ; or, again, 

 that coal-dust played the part that had been assigned to 

 '' outbursts of gas " by the colliery explosion experts and 

 inspectors of mines of that dav and of manv previous 

 years. 



In December of the same year, when an explosion, bv 

 which seventeen men lost their lives, occurred in a drv 

 and dusty district in Llan Collierv, near Cardiff. I made 

 a careful study of all the circumstances, attended the 

 inquest, and gave evidence * to the effect that in my opinion 

 coal-dust had been the paramount factor in the explosion ; 



1 Abridged from the Presidential Addres": delivered to the South Wales 

 '""[titute of Engineers on Januarv i8 bv Prof. W. Galloway. 



2 Published verbatim in the South Wales Daily Neivs of December 22, 

 and Ives tern i1/a// of December 23, 1875. 



NO 



. 2208, VOL. 88] 



that the coal-dust had been swept up from the floor. : 

 with the air, and ignited by the explosion and 



respectively, of a comparatively small volume of firtU 



and that this gas had itself been accidentally ignited \, 

 a naked light. 



-At the same time I made some further experiments wit! 

 coal-dust, as well as another scries to determine the h«»ig! 

 of the firedamp cap corresponding to various mixtu 

 air and firedamp containing carefully measured prop' 

 of each (a subjr-ct that had not been previously ii.w- 

 gated). I then prepared a paper entitled " On the Infli 

 (Mice of Coal-dust in Colliery Explosions," and through th 

 lato Dr. Frankland presented it to the Royal Society, tr 

 whom it was published in the following March (Proc. Ron 

 Soc, vol. xxiv., p. 354). 



Early in 1876 Mr. (now Sir Henry) Hall carried out hi 

 celebrated experiment with a blasting shot, and publishf! 

 an account of it in June of the same year; two year 

 later Prof. Marrecco and Mr. Morison, and four years 

 later Sir Frederic Abel, made experiments with coal-dust« 

 and in 1886 the two inspectors of mines Messrs. W. N. 

 (now Dr.) and J. B. Atkinson published a book describing 

 explosions in certain mines in their respective districts, 

 which they attributed to coal-dust. 



Owing chiefly, as can now be fully appreciated, to tl 

 small proportions of volatile matter contained in the t\ 

 kinds of coal-dust with which my experiments were mad 

 (about 16-5 per cent, and 18-5 per cent, respectively), and 

 partly, no doubt, also to the swiftness of the air-current 

 necessary to sustain it in suspension in the apparatus, I 

 had not up to this point proved that a mixture of air and 

 coal-dust, at ordinary pressure and temperature, could be 

 ignited by means of a naked light. On the other hand, I 

 had proved that, when less than i per cent, of firedamp 

 was added to such a mixture, it could be so ignited, and 

 continued to burn like a large jet of inflammable gas. 

 -Again, at p. 360 of my first paper I stated the opinion 

 that " if coal-dust could be made fine enough, and were 

 thoroughly mixed with dry air in the proportion of about 

 one pound to 160 cubic feet of air, the mixture might at 

 least be so nearly inflammable " (at ordinary pressure and 

 temperature) " that an explosion begun in it in a con- 

 fined space," like the workings of a mine, " might h' 

 propagated through it"; and, further, on September 7. 

 1878. I said, in Iron : — 



"It must not for a moment be supposed by anyone who 

 has perused the foregoing pages that because I have only 

 spoken of mixtures of air and coal-dust, or of air, coal- 

 dust, and firedamp, as forming feebly explosive mixtures. 

 I mean to imply that they cannot produce any. or all, of 

 the results observed in the most destructive explosions that 

 have ever been witnessed. I have constantly made use of 

 the qualifying expression " at ordinary pressure tempera- 

 ture," thereby signifying that their behaviour at extra- 

 ordinary pressure and temperature, such as are brought 

 into play when an explosion is begun in a confined spac^, 

 like the interior of a mine, may be, and probably is. ver\ 

 different." " That they do behave very differently has lonu 

 been my settled conviction. ..." 



I entertained no doubt in my own mind as to what result 

 would follow the initial stage, but in laying the question 

 before the Royal Society and others I could not go beyond 

 proved facts, and hence the necessity of approaching it 

 hypothetically in mv first paper, as follows (loc. cit., 



P- -S54).:— 



"If it could be shown . . . that a mixture of air and 

 coal-dust is inflammable at ordinary pressure and tempera- 

 ture there would be no difficulty in accounting for the 

 extent and violence of many explosions which have occurred 

 in mines in which no lar^e accumulations of firedamp were 

 known to exist ; for it is only necessary to suppose that a 

 sudden gust of wind (originated, for example, by the ex- 

 plosion of a small accumulation of firedamp) had swept 

 through the adjoining galleries, raising a cloud of dust into 

 the air. and then all the other phenomena would follow 

 in regular order. The flame of the originally inflammable 

 mixture would pass directly into the newly formed one. 

 expanding its volume ; the disturbance would be propagated 

 over an ever-widening area until that area might possibly 

 become co-extensive with the workings themselves ; and thp 

 consequences would be the same as if the whole space had 



