Sept. 29, 1881] 



NATURE 



513 



that the return-air from the ventilating shaft of a mine 

 may actually contain enough fire-damp to become inflam- 

 mable when coal-dust is diifused into it. In the third he 

 concludes that the influence of the coal-dust must not be 

 considered as merely aggravating and increasing the 

 explosion originating with the presence of fire-damp, but 

 that the presence of the dust must be regarded as the one 

 thing which, if a small explosion takes place anywhere, 

 will accumulate and carry forward the force of the explo- 

 sion with ever-increasing energy into every empty space 

 in the workings, however ramified. 



During the current year, experiments have also been 

 made on the subject; at Harton Colliery (Durham) by 

 Mr. Wood and Prof. Marreco, at Broad Oaks Iron- 

 works by the Chesterfield Committee of Engineers, at 

 Garswood Hall Colliery (Wigan), by Mr. Smethurst and 

 the Royal Commission on Accidents in Mines, and 

 lastly at Woolwich by Prof. Abel. The general character 

 of the experiments has been on a plan originally devised 

 by Mr. Galloway : viz. to expose to a flame, or to the 

 flash of a small cannon, a stream of air in a miniature 

 gallery into which any desired percentage of coal-gas or 

 fire-damp was introduced, and into which coal-dust could 

 be diffused by a hopper ; arrangements also being made 

 to raise the temperature of the gases, and to increase 

 their velocity at will. The majority of the exj erimenters 

 believe that in no case does a mixture of air and coal- 

 dust luitliout fire-damp explode, although the Chesterfield 

 Committee think they have evidence that flame will 

 travel in dust-laden air without a trace of fire-damp 

 being present. This matter is of great importance, for it 

 has been shown that in flour-mills explosions which have 

 occurred may be traced to the presence of combustible 

 dust in the air. 



Prof. Abel had placed in his care thirteen samples of 

 dust, some burnt, others unburnt — collected from differ- 

 ent parts of the Seaham mine ; which samples were sub- 

 jected to careful examination in the microscope, and to 

 chemical analysis. They were found to contain from 

 64'S3 to 9975 per cent, of pure coal-dust, some of them 

 containing ash, grit, and fine sand in various proportions. 

 They were then tested as to their power to aid in producing 

 explosions in an experimental gallery. The gas employed 

 was an explosive pit-gas, of such a quality that a mixture 

 containing only 3^5 per cent, of the gas with air when 

 travelling with a moderate velocity (from 200 to 1000 feet 

 per minute) was ignited by the flame of a naked Davy 

 lamp. In perfectly still air from 4 to 4'5 per cent, of the 

 same gas was necessary to produce the same result. 

 Currents of mixtures of this gas were conveyed into the 

 experimental gallery at a velocity of 600 feet per minute, 

 and at a temperature of 80° F. ; a naked Davy lamp, its 

 flame protected from the draught by a small screen, being 

 placed in the gallery at about 12 feet from the place 

 where the dust was supplied to the current. More 

 and more fire-damp was gradually added until explosion 

 took place ; that dust being regarded as most sensitive 

 which produced explosion with the least percentage of 

 fire-damp. When the relative sensitiveness of the various 

 samples of dust had thus been ascertained, it was found 

 that, of the four which stood head of the list in point of 

 sensitiveness, three headed the list also in point of rich- 

 ness in combustible matter and in point of fineness of 

 texture. But the sample which stood third in point of 

 sensitiveness was not only not the finest, but stood abso- 

 lutely bottom of the list, in point of richness. It there- 

 fore appeared that porosity and mechanical condition are 

 more important than combustibility of the dust in bring- 

 ing about the ignition of a fully explosive gas. Prof. 

 Abel was led, in consequence, to try whether fhe ignition 

 of a mixture of air and fire-damp in a low percentage not 

 inflammable of itself by contact with a lamp-flame could 

 be brought about by the agency of a wholly incombustible 

 dust. Accordingly dust such as calcined magnesia, pow- 



dered chalk, and slate dust was tried ; and it was found 

 that instantaneous explosion was thereby produced in 

 currents of air containing only 3 to 3'5 per cent, of fire- 

 damp. It appears then that dust of any kind, as a finely- 

 divided solid, can operate in determining the explosion of 

 an otherwise harmless mixture of gas and air ; probably 

 by furnishing, as the particles pass through the flame, 

 successive red-hot nuclei, by which the heat is localised 

 and rendered more intense. 



In the special case of dust that is both fine and com- 

 bustible, as coal-dust may be, it was proved that so small 

 a proportion of fire-damp as 2 per cent, in moderate 

 currents may determine the propagation of a flame by 

 coal-dust. Now, as it is stated on the best authority that 

 the most experienced eye cannot detect the presence of 

 2 per cent, of fire-damp by its effect on the flame of the 

 ordinary Davy lamp ; and as (in spite of all the host of 

 httle inventions to detect smaller percentages) the Davy 

 lamp remains the only practical test of the presence or ab- 

 sence of fire-damp in fiery mines, it follows that, in every 

 mine where there is any fire-damp <;/ all, the mere dust of 

 the mine constitutes an element of danger of which the risk 

 is simply incalculable. When we add to this that experi- 

 ments, made by firing such small blasts as eighty _§-rrt.-'«j 

 of gunpowder may represent, show that dust may cause 

 the propagation of flame in air-currents containing per- 

 centages of fire-dampyi?r smaller than any of those men- 

 tioned above, it is clear that whatever the risks with 

 Davy lamps may be, they sink into insignificance beside 

 the frightful dangers attending the firing of a shot for 

 purposes of blasting. The practice of blasting the coal 

 cannot be too emphatically condemned. It is at best a 

 lazy and slovenly process of getting the coal, and con- 

 sidering the ri-ks it entails, ought to be stringently and at 

 once put down by legislation. 



The practical moral is that, while the Davy lamp is to 

 be regarded more than ever as a necessary of work in 

 the pit, it cannot be regarded in any way as a safeguard 

 of ab.solute kind against explosion ; still less can it be 

 regarded as an indicator of the presence or absence of 

 impending danger, inasmuch as it is absolutely incompe- 

 tent to detect such feeble percentages of gas as Prof, 

 Abel has shown to be dangerous in the presence of the 

 inevitable dust of the mine. 



Science, which gave us the safety-lamp, must therefore 

 be called upon once more to provide efficient substitutes. 

 (i) .A new lamp, electric or otherwise, must be derised, 

 which shall be wholly independent of a supply of air 

 from the galleries in which it is used ; (2) an indicator 

 must be invented to do what the Davy lamp fails to do, 

 viz. to detect in the workings of the mine the presence of 

 a proportion of fire-damp less than 2 per cent, and to 

 indicate rapidly and accura:ely its amount. Let us hope 

 that Prof Abel will crown his labours by giving us such 

 new instruments. 



THE LANDSLIP AT ELM 



THE Swiss papers contain valuable information as to 

 the landslip which occurred on September 1 1 in the 

 valley of the Sernft River, in the canton of Glarus. The 

 month of September is notable in Switzerland for land- 

 slips. Thus the great landslip of the year 1618, which 

 buried the whole of the town of Plurs in Graubiinden, 

 with its 2340 inhabitants, occurred on September 4; and 

 the great downfall of the Rossberg Mountain, which de- 

 stroyed the village of Goldau, with three other small 

 villages, burying in houses and 457 persons, and filled 

 up the Lake of Lowerz, occurred on September 2, 1807. 

 The very heavy rains of the last few weeks have softened 

 the rocks on the slopes of the Plattenberg Mountain, 

 at the foot of which, at a height of 3330 feet, was situated 

 the village of Elm, now almost completely destroyed by 

 the landslip. The clay-slate quarries which were worked 



