488 



NATURE 



[February 9, 191 1 



A, which is called the downcast end, to F, a distance of 



.350 feet, which is shaded in the sketch. 



For seven minutes before, and also while the experi- 

 ment is being made, the fan draws air into and through 



-the gallery from its open end at the rate of between 50,000 

 and 60,000 cubic feet per minute- 



The dust employed in all the earlier experiments up to 

 the twenty-fourth was obtained from the colliery screens, 

 but in all subsequent experiments (exclusive of some made 

 with dusts from other localities and from abroad) it has 

 been produced by grinding nut-coal from the Silkstone pit 



>of Altofts Colliery in a disintegrator. The composition 

 and degree of fineness of the latter are as follows : — 



Moisture 



Volatile matter 

 Fixed carbon... 

 Ash 



3'2I 



33-68 



57-60 



5-51 



Intercepted by 

 100 mesh 7 25 



150 M 7"50 



200 , , 3-00 



240 „ 9-25 



Finer 73 'oo 



100 '00 



The quantity employed in an experiment is 1 lb. per 

 ; linear foot, or 0-39 oz. per cubic foot of air-space. It is 

 thrown on to the shelves by hand. 



It is usually ignited by firing a charge of 24 oz. of 

 gunpowder, tamped with 8 

 inches of dry clay, from a hole, 



2 inches in diameter by 2 feet l^-''" " ~ 

 ■9 inches deep, in a cannon, 1 > ;■ •: " 



called the igniter, placed in the 

 middle of the floor, pointinij 

 upwards at an angle of from 32 

 to 35 degrees, facing towards the 

 mouth of the gallery and at a 



distance from it of anywhere _ __\_— -^ ; _._ 

 between 260 and 360 feet, as the 

 case may require. But when 

 it is desired to take special pains 

 to secure ignition, as, for ex- 

 ample, when visitors are present, 

 a second small cannon charged 

 with 4 oz. of gunjX)wder and 



3 inches of clay-tamping, placed 

 at a point 90 feet nearer the 

 open end than the igniter in such 

 a position that it cannot ignite 

 the dust, is fired first so as to 

 raise a cloud of dust, which the 

 air-current then carries inwards 

 towards the larger cannon. Both 

 cannons are fired electrically, 

 the smaller one two seconds 

 before the larger. 



The discharge of the smaller cannon drives a cloud of 

 dust 4 or 5 feet long out at the op)en end of the gallery; 

 that of the larger cannon drives out a similar cloud 

 between 30 and 40 feet long. Then comes a rush of dust, 

 followed immediately ' by flame, which shoots out to an 

 average distance of 156 feet, in some cases to 180 feet, 

 accompanied by a loud report, which is said to be heard 

 at a distance of 35 miles. Finally, the flame rises up and 

 'ramifies into the cloud of coal dust which preceded its 

 first appearance, now floating in the air above it, and a 

 ..gieat volume of smoke and dust drifts slowly away. 



In Fig. 2 the open end of the gallery is seen at the 

 •right-hand side ; the white areas immediately in front of 

 it and in the smoke-cloud represent the flame. Fig. 3 is 

 a nearer view of the mouth of the gallery ' when an 

 explosion is in progress. 



All these phenomena, without exception, are identical, 



•except as regards magnitude, with those produced with 



mixtures of coal dust and pure air, " without the presence 



■of inflammable gas," in the Royal Society gallery in 



1880-1, in the Prussian gallery at Neunkirchen in 1884 



■<see later), and in Hall's experiments in the Big Lady pit 



in 1890, all of which the present writer has seen, as well 



as the Altofts experiment. 



On the other hand, the Altofts gallery is itself a mere 

 toy compared to one of the galleries, 5300 feet, or nearly 

 •twenty times as long, in Altofts Colliery, through which 



NO. 2154, VOL. 85] 



the explosion sped in a straight line in 18S6 ; and as llie 

 committee's own experiments, described in part ii., 

 chapter ii., have shown that the pressure and veloiiiy 

 increase rapidly with the length strewn with coal dust, it 

 seems somewhat absurd of the committee to propose to 

 make minutely correct observations of pressure, velocitv, 

 temperature, the size, shape, and composition of partii 

 of coked dust, and so on, with the idea that these obser\ 

 tions will be of some practical value in solving question- 

 relating to colliery explosions, which they rather in- 

 definitely class under the far-reaching title of "chemii ■' 

 and physical phenomena." 



A mine-waggon weighing 4J cwt., placed on the r;i 

 at a distance of 6 feet inside the gallery, ricochets alo 

 the surface of the ground in front to a distance of sevi 

 hundred feet when the explosion takes place. A simi 

 experiment was witnessed by Sir VV. Thomas Lewis .. 

 the present writer at the Prussian gallery at Neunkircli' ., 

 referred to above. The explosion itself is described in 

 Nature of November 6, 1884, p. 13, as follows : — " Ao/- 

 withstanding the entire absence of firedamp, there was a 

 true explosion of the most violent kind, and the clouds of 

 afterdamp which streamed from every opening darker 

 the air in the neighbourhood of the gallery for two 

 three minutes."^ A mine-waggon loaded with iron so ..c 

 to weigh 15J cwt., placed at the entrance to the gallery, 

 was driven up an incline rising at an angle of 4° to a 



Fig. 2.— Flame issuing from Downcast End. 



distance of 23 feet. The quantity of gunpowder used 

 the shot-hole was only 230 grams, or practically hall 

 pound. . . 



The observations (p. 21) regarding the_ position 

 deposits of coked coal dust on timbers fixed in the gal', 

 to represent props in a mine are for several reasons, ■ 

 of which is the baffling effect of the ventilating curr- 

 of no practical value as a means of throwing light upo:: 

 the point of origin of an explosion in a mine. 



Chapter iv., " On the Chemical Analysis of Coal Du?" 

 and chapter viii., entitled " Laboratory Investigation - 

 are intensely interesting and instructive, principally 

 account of the numerous, carefully thought-out devi 

 described in the latter for obtaining, collecting, :•■ 

 analysing the volatile constituents of coal, and if publi? 

 as a separate pamphlet would form a valuable addii 

 to the library of everyone interested in the analysis 

 mineral fuels. The methods of estimating volatile mat- 

 ash, and fixed carbon are practically the same as tlT 

 recommended by Dr. Pollard in the Memoirs of the Gr- 

 logical Survey.^ 



In chapter v. the instruments intended " for invest: 

 gating the mode of propagation of coal-dust explosions 

 (which, stated in plainer language, means those 

 measuring pressure, velocity, and temperature, and ' 



1 The italics are the reviewer's. 



2 The Coals of South Wales (1908), p. 7. 



