186 The Ventilation of Coal Mines. [April, 



place, carburetted hydrogen is constantly evolved. The following 

 are a few of Playfair's analyses of the Gases of coal-mines : — 





(1) 



(2) 



(3) (4) 



(5) 



(6) 



Oxygen «... 



0-9 





0-6 



30 





Nitrogen .... 



6-7 



6<4 



6-9 14-2 



12 3 



4-9 



Carbonic acid . . . 



0-7 



1-1 



0-3 2-1 



2-0 



1-7 



Light carburetted hydrogen 



91-8 



92-7 



92-8 83-1 



79-7 



93-4 



Hydrogen .... 



.. 







3-0 





Consequently we may infer that the production of the light car- 

 buretted hydrogen, which constitutes, when mixed with atmospheric 

 air, the explosive fire-damp, is either a continuation of the process 

 by which the coal has been formed, or that during the mutation 

 resulting, eventually, in coal, this gas has been largely developed, and 

 retained in the coal-bed, under enormous pressure, and consequently 

 in a most condensed form. Few persons who are not familiar with 

 our coal-beds have any idea of the state of high tension in which 

 the carburetted hydrogen exists in them. Mr. Thomas John 

 Taylor, who was one of the most experienced and scientific of our 

 colliery viewers, stated, before the Mining Institute of Newcastle- 

 on-Tyne, " that the mean annual quantity of gas evolved from a 

 barred-up district of fifty acres, in the Bensham seam at Wallsend 

 colliery, was thirty-four and a half millions of cubic feet, equal to 

 the solid contents of a coal-bed five feet thick and 160 acres in 

 extent." 



With this statement before us, it will be readily understood 

 how, when such a reservoir is suddenly tapped, by cutting a fissure 

 or otherwise, the outburst of gas must overpower the best possible 

 ventilation. Coal usually lies in widely extended beds, spread out 

 horizontally, or nearly so. The labours of the miner are directed 

 to the extraction of these beds from their seats, deep in the earth, at 

 the least cost, with the smallest waste practicable, and of course with 

 as little risk as possible. This is effected in several ways, in dif- 

 ferent districts, the principle observed being — by whatever method 

 the coal may be worked — to prevent the fall of the stratum above 

 the coal — " the roof " — when the coal is removed; and so to arrange 

 the " ways," that a constant current of air may circulate through 

 them. The more common methods are those called respectively 

 " pillar and stall " and " long- wall " working. In the first of these 

 large oblong pillars of coal are left to support the roof, and a 

 colliery so worked may be well represented, by placing piles of 

 books a few inches apart on a table, and covering all of them with 

 a board. The books will represent the pillars, and the spaces 

 between each pile , the passages of the mine. After a period, in 

 such a colliery, it is customary to " draw the pillars," for thus will 

 be obtained a large additional supply of coal. This is effected by 

 removing these oblong supports, beginning at the most remote part 



