20 



NATURE 



[May 4, 1882 



through it depends upon the state of division of the solid, and 

 the abundance of its distribution through the air. Under the 

 most favourable circumstances, the rapid combustion or explosion 

 of such a mixture is of a comparatively moderate kind, as it has 

 to spread from one isolated particle to another. With highly 

 inflammable solids, the rapidity of combustion under such condi- 

 tions is greatest, because, as each particle burns it also evolves 

 inflammable vapour, and is enveloped in flame « hich produces cor- 

 responding effects upon the immediately adjacent particles. In 

 order to ensure rapid and complete transmission of flame through 

 a mixture of inflammable dust and air, it is essential that the 

 former should be present in great abundance, for the foregoing 

 reasons, and that it should therefore be considerably in excess 

 over the supply of oxygen in the air. The facility with which, 

 under these conditions, flame may be transmitted by a dust-and- 

 air-mixture, with a rapidity calculated to produce more or less 

 violently destructive effects, according to the scale upon which 

 the combustion occurs and the degree of confinement of the 

 burning mixture, has been abundantly demonstrated by accidents, 

 many of them very disastrous, which have occurred in works 

 where large quantities of inflammable dust are unavoidably pro- 

 duced. Thus, in the grinding of sulphur, the inflammation of 

 dust of that substance, consequent upon the over-heating of a 

 shaft-bearing, has produced an explosion sufficiently violent to 

 destroy the chambers within which the operation was conducted. 

 In cotton mills, the accidental ignition of finely divided cotton 

 fibre floating in the air has led to the very rapid spread of con- 

 flagrations throughout extensive buildings. Even in a factory 

 where the spent madder, or guaracin°, is ground, whereby a 

 much less inflammable dust than that of cotton is produced, an 

 important explosion occurred a few years ago. But the most 

 numerous and extensive calamities of this kind have taken place, 

 and are still of frequent occurrence, in flour and rice mills. 

 Many such explosions, or very rapidly spreading conflagrations, 

 occurring in different parts of the continent and here, prior 

 to 1872, appeared enveloped in mystery, until their pro- 

 bable cause was indicated by an Austrian observer, and soon 

 afterwards made clear by Dr. Watson Smith, and espe- 

 cially by the careful inquiry which Me-srs. Rankin and Mac- 

 adam instituted into the very serious and fatal explo.-ion which 

 occurred at the Tradeston Flour Mills, in Glasgow, in 1S72. 

 The origin of this explosion was conclusively traced to the striking 

 of fire by a pair of millstones, through a stoppage in the feed of 

 grain, the results being the ignition of the mixture of flour-dust 

 and air by which the mills, inclosed in a chamber, were sur- 

 rounded, and the rapid spread of flame to the mixture of dust 

 and air which filled the conduits leading to the exhaust box, 

 which communicated with the several other mills and with the 

 stive-room. In this way flame was so quickly transmitted through 

 and to various channels and confined spaces in different parts of 

 the building as to produce violently explosive effects almost 

 simultaneously in different parts of the buildings. Messrs. 

 Rankin and Macadam ascertained that accidents of this nature 

 had increased in frequency since exhaust arrangements (for col- 

 lection of the fine flour) had been adopted in the more extensive 

 mills. The precautionary measures suggested by them were, 

 the adoption of efficient precautions for preventing the stoppage 

 of the feed to the millstones, the exclusion of naked flames from 

 the vicinity of these and the dust passages, and the construction 

 of the exhaust boxes and stive-rooms as lightly as possible, and 

 their location outside the main buildings. 



The liability to the development of fire or of heat sufficient 

 to char or inflame portions of flour by the stoppage of the feed 

 of grain, appears from all accounts to be extremely difficult to 

 guard against, and to have been the cause of many serious 

 calamities even since the Tradeston explosion, examples of 

 which are the great explosion of six mills at Minnesota in 187S, 

 when eighteen lives were lost and much property was destroyed ; 

 and the fatel and destructive explosion of a flour mill at Maccles- 

 field in September last, which has been made the subject of a 

 Report to the Home Office by Mr. Richards, of the Board of 

 Trade. It appears to be the opinion of experienced men in the 

 trade that, although special attention to the feed arrangements 

 may reduce the number of explosions, this cause of accident is 

 almost impossible to guard against ; while on the other hand, 

 many fires or explosions, ascribed to it, have been due to the 

 employment of naked lights in mills near localities where the air 

 is laden with flour-dust. Considering that flour- and rice-mill- 

 ouners have to bear the the burden of very heavy rates of insur- 

 ance, it is to their interest, independently of their responsibilities 



as the guardians of the lives of their workmen, to adopt most 

 stringent regulations and efficient precautionary measures for 

 abolishing this source of danger, and to devote their energies to 

 the application of improved arrangements for reducing the 

 quantity of dust which passes away from the millstones and from 

 other parts of a flour mill. 



The important part played by coal-dust, which exists in greater 

 or less abundance in coal-mines, in aggravating and extending 

 the injurious effects of fire damp explosions, was originally 

 pointed out early in 1845 by Faraday and Lyell, when they 

 reported to the Home Secretary the results of their inquiry into 

 an explosion which occurred at Haswell Collieries in September, 

 1844. That Report, which was published in the Philosophical 

 Magazine for January, 1845, dealt exhaustively with the cause 

 of the explosion, and the means by which a recurrence of such 

 a calamity might be guarded against, and the latter subject was 

 again discussed by Faraday in a lecture delivered at the Royal 

 Institution in February, 1845, and in a letter published directly 

 afterwards in the Philosophical Magazine. It is pointed out in 

 Faraday and I .yell's Report, that in considering the extent of 

 the fire from the moment of the explosion, fire-damp mu-t not 

 be supposed to be the only fuel, for that the coal-dust swept up 

 by the rush of wind and flame from the floor, roof, and walls of 

 the working would instantly take fire, and, in support of this 

 statement, they refer to considerable deposits of dust in a par- 

 tially coked condition which they found adhering to the faces of 

 pillars, props, and walls where the explosion had occurre 1 and 

 the fire had extended. An examination of these deposits showed 

 that the coal was deprived more or less completely of its bitu- 

 minous constituents, and they concluded from this that the ex- 

 posure of the dust to the flame of the exploding gas-mixture 

 gave rise to the generation of much conl-gas from it, the carbon, 

 or coke, remaining unburnt only for want of air. 



Ten years after the publication of Faraday and Lyell's Report, 

 M. de Souich, an eminent French mining engineer, published, 

 as original, some very similar observations made by him on 

 examining the effects of a coal-mine explosion at Firminy ; he 

 noticed, moreover, that men near the pit's month had received 

 burns, « hile others who were in the workings near the seat of the 

 explosion, but out of the main air current, escaped unhurt, and he 

 ascribed this to the action of coal-dust in carrying flame along the 

 principal air-way. Later on, De Souich extended his inquiries 

 into the part played by coal-dust in explosions, and the subject 

 was afterward s pursued from time to time in France by Verpilleux 

 and other authorities in mining engineering, and especially by 

 M. Vital in 1875, when an explosion occurred at Campagnac, 

 the de- tractive effects of which appeared to him in a great mea- 

 sure ascribable to coal-dust. Vital made experiments upon a 

 very small scale for the purpose of ascertaining whether flame, 

 such as that projected into the ail of a mine by the firing of a 

 charge of powder, in a very strong blast-hole, was increased in 

 size by the presence of suspended coal-dust ; and soon after- 

 wards Mr. W. Galloway commenced a series of experiments 

 of a similar nature, but upon a larger scale, which he has con- 

 tinued from time to time up to the present date ; while Messrs. 

 Marreco and Morison, in connection with the North of England 

 Institute of Mining Engineers, and a committee of the Chester- 

 field and Derby Institute of Engineers, have also contributed 

 valuable experimental data bearing upon the influence exerted 

 by coal-dust, not merely in increasing the magnitude of explo 

 sions resulting from the ignition of mixtures of tire damp and 

 air, but also in propagating or even actually developing explo- 

 sions, when only small quantities of fire-damp are present in the 

 air of a mine, or where fire-damp is believed to he e itirely 

 absent. The conclusion to which Mr. Galloway was led by his 

 earlier experiments was to the effect that coal-elust, when thickly 

 suspended in air, had not the power to originate an explosion, 

 or to carry on to any distance the flame Irom a blown-out shot, 

 but that the presence in the air of such small quantities of fire- 

 damp (2 per cent, and under) as an experienced miner would 

 fail to detect by means of his Davy lamp, with which the gas is 

 generally searched for, would impart to a mixture of coal-dust 

 and air the property of burning and carrying flame. But he 

 held the view at the same time, that a fire-damp explosion in 

 one part of a mine might be propagated to some extent by coal- 

 dust raised by the effects of the explosion in parts of the mine 

 where no fire-damp existed. Marreco, on the other hand, con- 

 sidered that the results of certain experiments made in the entire 

 absence of coal-dust, by firing shots in air travelling at some 

 considerable velocity, and containing coal-dust thickly suspended 



