MINING 315 



consider the state of the workings in the mines of Eammelsbcrg. We may remark 

 in fig. 1475 the regularity of the vaults previously scooped out above the level BC, 

 and the other vaults which are in full activity of operation. It is, therefore, 

 towards the lower levels that the new workings must be directed. For this 

 purpose, the transverse gallery being already completed, there is prepared on the 

 first of these floors a vault of exploitation at b, which eventually is to become 

 similar to those of the superior levels. At the same time there is commenced, at 

 the starting-point below it, reached by a small well dug in the line of the mineral 

 deposit, a transverse gallery in the rock, by means of blasting with gunpowder. 

 The rock is also attacked at the starting-point by a similar cut, which advances 

 to meet the first perforation. In this way, whenever the vaults of the level c are 

 exhausted of ore, and terraced up with rubbish, those of the level beneath it will bo 

 in full activity. 



Others will then be prepared at a lower level ; and the exploitation may afterwards 

 bo driven below this level by pursuing the same plan, by which the actual depth of 

 excavation has been gained. 



In workings by fire we must distinguish : 1, the case where it is necessary to open 

 a vault immediately from the floor ; 2, the case where, the vault having already a 

 certain elevation, it is necessary to heighten its roof. In the former case, the wall or 

 floor of the mineral deposit is first penetrated by blasting with gunpowder. As soon 

 as this penetration is effected over a certain length, parallel to the direction of the 

 future vault, as happens at b, there is arranged on the bottom a horizontal layer of 

 billets of firewood, over which other billets are piled in nearly a vertical position, 

 which rests upon the ore, so that the flame in its expansion comes to play against the 

 mineral mass to be detached. When, after some similar operations, the flame of the 

 pile can no longer reach the ore of the roof on account of its height, a small terrace 

 of rubbish must be raised on the floor of the deposit ; and over this terrace a new 

 pile of faggots is to be heaped up as above described. The ancient miners committed 

 the fault of constantly placing such terraces close to the roof, and consequently 

 arranging the faggots against this portion of the ore, so that the flame circulated 

 from the roof down to the floor. The result of such procedure was the weakening of 

 the roof, and the loss of much of the ore which could not be extracted from so unstable 

 a fabric ; and, besides, much more wood was burned than at the present day, because 

 the action of the flame was dissipated in part against the whole mass of the roof, 

 instead of being concentred on the portion of the ore which it was desired to dislodge. 

 How, the flame is usually made to circulate from the floor to the roof, in commencing 

 a new vault. 



When the vault has already a certain height, care is always taken that between 

 the roof of the vault and the rubbish on which the pile is arranged, no more 

 than two yards of space should intervene, in order that the flame may embrace 

 equally the whole concavity of the vault, and produce an uniform effect on all its 

 parts. Here, the pile is formed of horizontal beds, disposed crosswise above one 

 another, and presents four free vertical faces, whence it has been called a chest by 

 the miners. 



It is usually on Saturday that the fire is applied to all the piles of faggots 

 distributed through the course of the week. Those in the upper floors of exploi- 

 tation are first burned, in order that the inferior piles may not obstruct, by their 

 vitiated air, the combustion of the former. Thus, at 4 o'clock in the morning, 

 the fires are kindled in the upper ranges ; from pile to pile the fireman and his 

 assistant descend towards the lower floors, which occupies them till 3 o'clock in the 

 afternoon. 



When the flame has beat for a few instants on the beds of ore, a strong odour of 

 sulphur, and sometimes of arsenic, is perceived ; and soon afterwards loud detonations 

 are heard in the vaults. Suddenly the flame is seen to assume a blue colour, or even 

 a white ; and at this period, after a slight explosion, flakes of the ore, of greater or 

 less magnitude, usually fall down on the fire, but the chief portion of the heated 

 mineral still remains fixed to the vault. The ores pass now into a shattered and 

 divided condition, which allows them afterwards to be detached by long forks of iron. 

 In this manner the fire, volatilising entirely some constituents, such as sulphur, zinc, 

 arsenic, and water, changing the aggregation of the constituent parts of the ore, and 

 causing fissures by their unequal expansibilities, facilitates the excavation of such 

 materials as resist by their tenacity the action of gunpowder. 



The combustion goes on, without any person entering the mine, from Saturday 

 evening till Monday morning, on which day the fireman and his assistants proceed to 

 extinguish the remains of the bonfires. On Monday, also, some piles are constructed 

 in the parts where the effect of the former ones has been incomplete ; and they are 

 kindled after the workmen have quitted the mines. On Tuesday all hands are em- 



