BORING 



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required. The general plant consists of the boring machine, this being a cylinder 

 having steam applied to the upper side of the piston only. The piston-rod is attached 

 to one end of a massive beam, to the other end of which the boring tools are sus- 

 pended. The capstan engine c, is used for lowering and raising the boring tools, and 

 for raising the debris made by the boring. 



2nd. When the stage B B, on which the borers stand, has been erected, the boring' 

 of the pits is commenced. Supposing that the pit to be sunk has a diameter of 13 feet, 

 the first process is to put down a borehole, with a diameter varying from 3 to 5 foot, i 

 and the tool used for this hole progresses in ordinary strata, at the rate of about . 

 8 feet per day. When this hole has been put down, say a distance of 60 feet, the 

 larger trepan used for the purpose of making the pit its full size is applied. This ' 

 instrument is shown "by figs. 188 and 189 ; it is made of wrought iron, is furnished with i 

 28 teeth or chisels, and weighs about 16 tons. The smaller trepan is of similar design. 



188 



189 



31 



tar 



i 



ill] 



The ordinary speed of the boring when worked by the large trepan may be taken at 

 about 3 foet per day. It will be observed that the faces of the chisels incline to the centre 

 of the pit ; this tends to assist the passing of the debris made in the large boring into 

 the cavity formed by the small boring tool, whence it is extracted by the ordinary 

 scourer. This process is continued to the bottom of the aqueous strata, the small 

 borehole being kept about 60 feet in advance of the larger hole. Should broken tools 

 fall into the shaft, the instruments shown by figs, 190 and 191 are used, the former, 

 by means of internal teeth, clutches with ease broken bars, &c., having no shoulder, 





and which cannot bo taken hold of by means of the ordinary extractor. Fig. 191 is 

 the 'grapin,' used for the purpose of raising broken teeth or other small objects 



which may have fallen to the bottom of the shaft. This tool has one part sliding into 

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