150 watts: coal-dust and explosions in coal-mines. 



air-current into an explosive mixture. Therefore, adopting the 

 former simile, as the dant is the tinder^ so this is the sulphur match. 



So far, artificial dusts have been considered ; now we will deal 

 with dust natural to deep dry pits. The dust in such pits is mainly- 

 produced within the pit itself, but some is brought (you may readily 

 see it sparkle in the sunshine over the pit-mouth) by the intake air- 

 current from the screens. As this does not differ in composition 

 from that which has never left the pit, it need not be dealt with 

 separately. It needs only to be mentioned that it is but the very 

 finest particles that are thus borne back on the wings of the wind 

 into the pit. 



The dust produced within the pit itself is formed during the 

 processes of hewing and hauling, especially the latter. The working 

 face is troubled by no large amount, and it is entirely bottom dust. 

 The haulage ways are the special homes of the dust. , Here it exists, 

 in the greatest quantities and in all the varieties of bottom, upper, 

 and flocculent. It is partly shaken out of the moving tubs, partly 

 blown out by the strong ventilating current. It must be remembered 

 that the force of this wind can only be appreciated by adding together 

 the speed of the current and the rate of the haulage. That which is 

 shaken out goes mainly to form bottom dust ; only the finest particles 

 getting lodged on roof timbers and natural ledges. That which is 

 blown out goes much more largely to form upper and flocculent dust. 

 The mechanical force necessary to render the coal very fine is greatly 

 in excess of that needed to reduce the dant to the same degree of 

 fineness ; indeed, great force is necessary in the one case and a mere 

 touch or jolt is sufficient in the other. This must be borne in mind 

 when the relative amounts of coal and dant are compared in the 

 solid coal and in the pit dust. The proportion of dant in the finest 

 dust is very largely above that in ordinary coal. 



Falls of stone, the making of refuge holes, and the natural wear 

 of the floor, cause an admixture of stony matter, and the constant 

 passage of horses and men, the carriage of timber, bricks, &c., 

 introduce other extraneous and incidental matters ; but all these 

 latter are small in amount and do not materially affect the character 

 of the dust in intake haulage- ways. 



The dust in return airways is usually only bottom dust in all 

 essentials, and here the efl"ects of falls from roof and sides, and from 

 the beating-up of the floor, are found at their maximum, so that the per- 

 centage of stone is usually in the ascendant. It is not, therefore, here 

 that the dust is dangerous. The great danger here is gas, since the air in 

 these returns has circulated through the mine. It is a most significant 

 fact that in the great majority of late disastrous explosions, the track 



Naturalist^ 



