362 



MINE. 



Mines of 

 Coal. 



It has been stated by some, that this gas has only 

 been found in mines which are wrought under the 

 level of the sea ; it is admitted that it has been found 

 most abundant in such cases, but it abounds also in 

 districts much elevated above that level. 



This air is either formed with the coal, or generated 

 afterwards, according to the opinions of different phi- 

 losophers. One thing is certain, that as soon as a 

 coal containing this air is wrought, the air exudes from 

 every pore with a hissing sound ; if the coal is of close 

 'texture, and when a cutter or open fissure is struck, it 

 comes off not only quickly, but with immense force, 

 and with a noise similar to the issuing of steam from 

 the safety valve of an engine boiler. This violent is- 

 sue of gas is named a blower ; and if by accident it is 

 ignited, its force is such, that it will act like an im- 

 mense blow pipe, and set on fire the coal upon the 

 opposite side of the mine, and also at the mouth of 

 the blower. And there have been instances,' where, in 

 working a bed of coal under another coal, with seven 

 feet of argillaceous strata betwixt them, and when 

 the upper coal abounded with inflammable air, this 

 gas, from its elasticity, forced down the stratum seven 

 feet thick, although the mine was only four feet in 

 width. These facts clearly prove that this gas abounds 

 in coal, in a state highly compressed, and consequently 

 very elastic. From this cause it is generally found 

 that the coals abounding with this gas are the easiest 

 to work. 



It frequently happens that cutters and fissures in the 

 sand-stone, and other accompanying strata of coal, 

 yield this gas in great quantity ; but it is never once 

 doubted but that all this gas flows directly from beds 

 of coal. It has likewise been found uniformly in the 

 practice of mining, that in most cases this gas abounds 

 in uncommon quantity when the miners approach a 

 great dislocation or slip of the strata, and the fissure of 

 the dislocation yields not only the gas in great quanti- 

 ty, but the issue will continue for years, and sometimes 

 during the whole working of the colliery. This cir- 

 cumstance is easily accounted for, because these dislo- 

 cations extend from the surface of the rock, to depths 

 hitherto impenetrable. Hence a dislocation with an 

 open fissure connects together every bed of coal to the 

 greatest depth, and gives vent to the inflammable air 

 of each, like a train connecting a number of maga- 

 zines of inflammable matter together ; whereas in the 

 common fair lying coal-field, each body of coal is in- 

 sulated from the other coals by strata which are fre- 

 quently impervious both to air and to water. There 

 are instances of coal-fields, where in working the 

 coals in various beds, a particle of this gas was never 

 seen ; yet upon striking a slip or dislocation, it imme- 

 diately issued, though seldom in such instances in any 

 great quantity. 



It is farther to be remarked, that this gas is not on- 

 ly found formed, and pent up in the cavities and fissures 

 of the coal from which it flows freely, when these ca- 

 vities and fissures are opened, but it appears to exist 

 also in the minute and invisible pores of the compact 

 body of the coal, especially in the caking coals, which 

 have a bright steel grained fracture ; besides which, it 

 is chemically combined with the substance of the coal, 

 which circumstances account, in some degree, for its 

 constant formation in particular cases. In proof of which, 

 we have to state, that after coals of the above descrip- 

 tion have been exposed above ground to the action of 

 the atmospheric air, if a quantity of them are pounded 

 under water, gas will escape in considerable quantity ; 



which gas is the carburetted hydrogen. A singular Mines o 

 circumstance has also occurred within these few years ; Coal, 

 when loading vessels with these coals, newly wrought, ^~^f~* 

 and allowing them to fall into the vessels from a con- tj j"' 

 siderable height, gas has been produced in such quan- 

 tity, that after the hatches were secured, and the ships 

 ready to proceed to sea, the gas has ignited at a candle, 

 scorching the seamen, blowing up the decks, and great- 

 ly injuring the vessels. 



When pillars of coal are forming below ground, for 

 the support of the superincumbent strata, much gas 

 flows from the fore-heads of the boards or rooms ; but 

 as soon as the pillars are formed, or the mass of coal 

 insulated from the main body of the whole wall, the 

 issue of gas from the pillars almost instantly ceases; 

 but when by misfortune, a creep or crush comes upon 

 the pillars by the enormous pressure of the strata, a 

 great flow of gas is produced from the pillars into the 

 waste, an effect which may be compared to the squeez- 

 ing of water from a sponge. 



The gas which exists in the coal in chemical combi- 

 nation, can only be driven off by actual burning in a 

 common fire, or by distillation, to which a high degree 

 of heat is applied, as in the manufacture of gas light. 



All caking and open burning coals contain this gas 

 in very great quantity, yet there are very singular ano- 

 malies regarding its combination with them. From 

 what is before stated, the fine caking coals yield this 

 gas in greatest quantity in the course of mining; but 

 when exposed to the air it retains the gas in larger pro- 

 portion than the other kinds of coal, yet on distillation, 

 it yields less gas from a given weight of coal. On the 

 other hand, the open burning coals, which generally 

 yield much less gas in mining, when exposed to the air 

 lose a great proportion of it, so much so, that after a 

 twelvemonth's exposure they burn in a common fire- 

 place with a dull flame, termed dead burning ; and in 

 place of forming a good coke or cinder, produce a 

 great quantity of ashes ; yet these open burning coals, 

 if kindled when wet from the mine, burn with a bright 

 vigorous flame, an intense heat, and form a good coke 

 or cinder. The pitch coal, known by the names of 

 bottle, parrot, or cannel coal, yields little, if any, of this 

 gas in mining, whereas in distillation it gives a much 

 greater produce than any other of the coals, and is, on 

 this account, greatly preferred in the manufacture of 

 gas light. This gas being lighter than common air, 

 always ascends to the roof or to the rise parts of the 

 colliery, and where the dip is considerable, occupies the 

 forehead of the mine in a wedge form, as represent- 

 ed Fig. 16. Plate CCCXCIII. Where a is the in- p lATE 

 flammable air, and b the common air, in this case a cccxcm. 

 candle will burn without danger, near the point c, next F'g- 16. 

 the roof, whereas, if it is advanced a few feet farther, 

 an explosion will instantly take place, it being well 

 known, that at the line where the two airs are in con- 

 tact, they mix and form a fringe of air highly explode- 

 able. 



When this gas abounds in the mines, and is mixed 

 in great proportion with the common air, the workmen 

 breathe it without suffering any inconvenience at the 

 time, and although they work amongst it for a succes- 

 sion of years, their health does not appear to be affect- 

 ed by it ; but if a miner enters amongst pure carburet- 

 ted hydrogen, the instant he takes one inhalation he 

 drops down as if shot, and the whole living principles 

 are completely and instantly suspended ; those who 

 have seen such an accident take place, were greatly 

 astonished at its instantaneous operation on the animal 



