AND PREVENTING ITS EXPLOSION. 49 



must therefore rather be regarded as a new and continued pro- 

 duction. There is no operation from which, under this point 

 of view, it can be derived with so much probability as from the 

 slow decomposition of water permeating the coal ; and the con- 

 nection of the production of carbonic acid with the carburetted 

 hydrogen, seems to prove that this is its origin. That water 

 transuding slowly through a mass of coal, and existing in it in 

 some measure under pressure, will be decomposed, is, from the 

 consideration of the general agency of water on carbonaceous 

 substances, extremely probable. The evolution of the same gas 

 from marshy situations, there is every reason to believe, de- 

 pends on the decomposition of water by carbonaceous matter ; 

 and the occurrence, not unfrequent, of large masses of small 

 coal accumulated at the mouths of the pits, and exposed to 

 humidity, taking fire spontaneously after a certain time, can 

 scarcely be ascribed to any other cause than to such a decom- 

 position, and may therefore be regarded as a proof of it. 

 There are circumstances, too, connected with the production of 

 fire-damp which seem to prove that this is its origin. Thus it 

 does not occur in all coal-mines ; in some it is abundant, in 

 others it is almost unknown ; and this seems to be considera- 

 bly dependent on the state of humidity in the coal. In the 

 collieries in this country, — for example, fire-damp scarcely ever 

 occurs in those of Mid Lothian ; while in those of West Lo- 

 thian, of Stirlingshire, Fife, and Ayrshire, it is not an unfre- 

 quent occurrence ; sometimes to such an extent as to have 

 -been productive of considerable explosions, and in some of 

 these mines its evolution is nearly constant, so that it is a re- 

 gular practice to remove it by firing it. I have been able to 

 discover no cause for this peculiarity, but the comparative state 

 of dryness and humidity. It is not owing entirely to the depth, 

 for this differs little ; in some of the mines of Mid Lothian, 

 Vol. VIII. P. I. G the 



