188 The Ventilation of Coal Mines. [April, 



is called "cleat." In cutting across these fissures, more gas is 

 liberated than when working " headways course," or parallel to those 

 fissures. Thus we learn that gas is not generated in the coal 

 during the process of working, or by the release of pressure ; but, 

 that it is poured out of cavities, in which it has long been pent up, 

 because these cavities are laid open. The more free and open the 

 cleat structure, the more easy and regular the flow of the released gas. 



From the quantity of nitrogen detected by Playfair in the gases 

 examined by him, it has been supposed by some that atmospheric 

 air has permeated the fissures of the coal, and set up chemical 

 action ; " for we are ignorant of any process of decomposition which 

 would eliminate it in an isolated form. The process of decay and 

 putrefaction would cause its separation as ammonia, and the action 

 of heat would produce the same effect." The presence of carbonic 

 acid — always, however, in small quantities, — which bas been detected, 

 has been adduced as further evidence of the action of atmospheric 

 air on the coal, after it has been opened by the miner. These 

 hypotheses are unsupported by the evidence we obtain in the pits. 

 Every stage in the operations of the miner shows that this 

 carburetted hydrogen has been accumulating for ages in the mass of 

 the coal, and that it is liberated in the process of working out the 

 bed of coal. 



It should not be forgotten that coal-beds vary very greatly in 

 respect to their gaseous accumulations. There are some districts 

 in which " fire-damp " is unknown. There are even beds of coal 

 which contain much carburetted hydrogen in some parts, while 

 other parts are entirely free from this gas. It is not easy to 

 account for this difference. In all probability, the age of the coal, 

 the conditions under which the coal was formed, and the length 

 of time during which the masses of coal-plants were exposed to 

 atmospheric conditions, before they were buried under the strata of 

 sand and shale which now cover them, determined the physical 

 conditions of the bed. 



Some idea may be formed of the rapidity with which the 

 inflammable gases pour forth by an example or two. On one occa- 

 sion at Seaton-Delaval, 4,900 cubic feet of gas were evolved in three 

 minutes. At Hebburn colhery, where the process was continuous, 

 about 1,500 cubic feet of explosive mixture was formed in two 

 hours. Occasionally the outburst of gas is with explosive violence, 

 overpowering any system of ventilation which can be established. 



Such are the circumstances, — very briefly stated, — of the con- 

 ditions under which the dangerous atmospheres of our collieries are 

 produced. Let us now examine the methods which are adopted to 

 secure the removal of those dangerous gases as quickly as they are 

 formed. 



It is well known, that as we descend into the Earth, by means 



