216 



MINING 



say, in immping into tin- iioii cylinder that forms 

 tin' shall such HII amount of iiir that the pressure 

 on the hottom from \\iihin should beMUMtO that 

 from without. I'.y means of 11 flooring in tlie 

 cylimlcr, a lower airtight compartment is formed, 

 in which it is fouml that men ran work umlcr a 

 pressure of 3J atiim-pln-ii-. In order that the men 

 may enter or leave their working-place without 

 diMurhing the e<|iiilil>rium of the forces, the prin- 

 ciple of the canal-lock is applieil, a second chamber 

 bein;; formeil aluve the working one with trap- 

 doors communicating with the shaft alwve and 

 with the chanilier bwow. One of these doom lieing 

 always closed while the other is open, the excavated 

 material can be drawn up without any appreciable 

 1"-- of compressed air. This method has been 

 successfully applied at a number of shafts on the 

 ('oiitim -lit. 



Another ingenious process of sinking through 

 quicksand is that devised by II. 1'oet-eh. ThU 

 consists in freezing the water contained in that 

 portion of the water-l-oaring ground which occupies 

 the position of the intended ..haft into a solid mass 

 of ice, and then sinking through it by hand without 

 having to pump any water. This method has 

 proved succe-ssf ill at several Continental collieries 

 and at the Chapin mine in Michigan. 



The average depth of coal-mines before the intro- 

 duction of the steam-engine did not exceed 100 

 yards, whilst a near approximation for the present 

 time would Ive 400 yards. The deepest shaft in 

 < iieat Britain is that of the Ashton Moss Colliery, 

 near Manchester, which has attained a depth of 

 JvMl feet. The seams dip at tlie rate of 9 inches 

 p-r yard, so that parts of the workings are 3000 

 feet deep. The deepest shaft in the world was 

 until recently that of a silver lead mine in Iloliemia, 

 at I'r/.ibram. where the Adalbert shaft is 3432 feet 

 in depth. This depth has, however, UMIII exceeded 

 in the Lake Superior copper-mining district, where 

 in I S'.MI the Calumet shaft attained a depth of 3900 



The cutting of a path through the harder rocks, 

 as carried on by the ancient miners, was particu- 

 larly laborious. The work was executed in con- 

 fined spaces, and a large amount of dust was 

 produced. The miners' vocation was excessively 

 unhealthy, inasmuch as they were obliged to inhale 

 large quantities of dust ; they thus becalm- subject 

 to disorders of the lungs to which they fell victims 

 at an early age. Previous to tin' introduction of 

 blasting the implements used were of the nature 

 of wedges and hummers. Hit by bit pieces of rock 

 were broken away, the o|M-ration lieing aided by 

 natural fissures in the rock and by the hrittlcness 

 of tin; hard material. In this way the ancient 

 miners cut coffin-shaped galleries ,"> feet in height. 

 At the present time the galleries or levels are 

 usually "^ feet high and ' feet wide, thus atl'ording 

 great facility for travelling and for ventilation. 

 Tin' invention of gunpowder is of much greater 

 antiquity than its application to mining purposes. 

 In the 1 tth century it was largely used for musketry 

 and cannon, and even fm -blowing down defences ; 

 but. curiously enough, it was not applied to mining 

 purpose* until the l-eginning of the 17th century, 

 and even then made it- way so slowly that it was 

 not largely employed until the ISth century. In 

 the o|x-ralion of blasting use is made of a borer or 

 drill of iron, or, as is more usual, of cast-steel. 

 This is struck with a hammer. A 1-orer of larger 

 diameter may be used, held by one man ami struck 

 by another. < f late years mechanical rock-drills 

 driven by steam or by compressed air have come 

 largely into use; see Bm.-isc., with illustration. 

 The bore hole, when finished, is then charged. 

 Tlie guii|M.wder is enclosed in a little bag of cloth 

 in pitch and provided with a fuse. Instead 



of using a cartridge of this kind, clay may l>e 

 , down the boli- by a claying bar so as to -hut 

 oil feeders of water, and the nole will be dry 

 enough to receive a charge of powder. A needle of 

 iron or steel is placed in the midst of the charge 

 with the ring at its end protruding, and tamping 

 i> introduced. For this purpose it is best to put 

 in clay piecemeal until the whole is tilled up. 

 Accident." may happen by pushing down the iron 

 liar, which is apt to strike lite against haul rock. A 

 second suspected canst* is that, when a man takes a 

 tamping bar and strikes it with a hammer, the air 

 is compressed, and the temperature augmented 

 sufficiently to explode the '-owder. The-e di- 

 advantages are set aside In Mes-rs Birkford & 

 Smith's safety-fuse (see BLASTING). The older 

 fuse consisted of carefully selected straws filled 

 with fine powder The safety fuse is of cotton 

 with gunpowder in the middle. For use in wet 

 ground it i- covered with a waterproof composition. 

 Considerable attention has been paid to the subject 

 of consolidating the charge. Excellent work has 

 been done with compressed powder ; dynamite has 

 become quite indis|H*nsable ; and gun-cotton is 

 also employed, the best form living the compressed 

 Variety invented by Abel. Nitrated gun-cotton or 

 tonite has also given admirable results. The 

 fullest benefit of these modern explosives can only 

 be obtained by the use of strong detonators fired 

 by electricity, by which it is possible to place a 

 number of bore-holes in such a manner that when 

 fired simultaneously they shall help each other. 



For removing coal these high explosives are too 

 quick ill their action, and blasting powder con- 

 tinues to lie used. Millions of tons of coal are still 

 obtained by its aid. In order to obviate the danger 

 of explosions in fiery collieries, many ingenious 

 substitutes for blasting have been proposea. For 

 example, a hole is lioicd, and wedges inserted to 

 force down the coal which has previously been 

 under-cut with the pick. Another plan of great 

 promise is that devised by Smith and Moore, in 

 which cartridges of cau.stic lime are employed, 

 water being forced into them by a force-pump. 

 The pressure of steam generated by the usual 

 charge of seven cartridges is 2850 Ib., the car- 

 tridges themselves expanding to about five times 

 their original si/e. The elltciency of these car- 

 tridges varies with the nature of the coal, the be-t 

 results having been obtained in the Derbyshire 

 collieries. 



The work of tlie miner engaged in under-cutting 

 the coal >eam is very arduous, and \aiious coal- 

 cutting machines have been invented with a view- 

 to lessen the labour and expense. They work with 

 compressed air or electricity, and have the cutters 

 arranged on the periphery of a rotating disc, or on 

 a travelling pitch-chain. Though largely employed 

 in America, they have not yet come into extensive 

 use in Great Britain. The coal, when broken 

 down, i- placed in wagons, ami drawn by hoi si's or 

 engine. power to the 1-ottom of the shaft and raised 

 to the surface. 



The actual mode of working the coal, although 

 varying greatly in every distiict. may be broadly 

 divided into (1) the post-ami stall, or bold and 

 pillar, or (in Scotland) stoop-and-room, method, 

 where the first stage of excavation is accomplished 

 with the roof sustained by coal ; (2) the long-wall 

 method, where the whole of the coal is allowed to 

 settle lieliind the mi nets, no sustain ing pillars of coal 

 being left. The latter method, when well planned, 

 i- the safer l-nth a-s regards facility of ventila- 

 tion and less liability to accidents from falls. At a 

 Durham colliery, working the Harvey seam, which 

 is 3i feet in thickness, 5185 tons of coal were 

 obtained when working by the long-wall system, 

 and .jori-j tons when working by the post-and-stall 



