450 



BORING 



the other, and is lowered with the claws closed. An arrangement of light ropes 

 handled from the surface enables the engineer to work this instrument. 



3rd. Placing the Tubing. Instead of being in small segments, the tubing is cast in 

 complete cylinders, about 5 feot high, with inside flanges at both top and bottom, 

 which are turned and faced. The tubing is suspended in the pit by rods, and is 

 lowered down as each new cylinder is added. When the bottom of the water-bearing 

 strata is reached, the arrangement shown by .$7. 193 is adopted. A sliding moss-box, 

 placed inside the base of the tubing, is allowed to rest on the rock floor made for the 

 reception of the tubing, at the point below which no feeders of consequence are ex- 

 pected. The full weight of the tubing resting on this box, causes the moss to protrude 

 at the back, and form a perfectly water-tight joint at the base of the tubing. To 

 render this joint more secure, a few feet of tubing in segments resting upon two strong 

 wedged curbs, are placed in the pit below the moss-box. 



190 



191 



192 



193 



i 



4th. The Securing of the Rigidity of the Tubing. The tubing now, as it were, 

 stands in the pit, resting on the foundation afforded by the moss-box, but without any 

 lateral support. It is secured in its -position by means of cement, which is dropped 

 down behind the iron tubing by means of a cement-box with a moveable piston, worked 

 by a rope from the surface. (Seofy. 192). 



5th. The shaft having now been made secure, the extraction of the water is pro- 

 ceeded with, and the pit is then ready to be sunk either by the ordinary method or 

 otherwise. 



The labour and time taken in the changing of the rods becomes so great at consi- 

 derable depths that the ordinary system of sinking has generally to bo resorted to. 



Boring in Coal. An important operation in coal-mines, where explorations have to 

 be made in the direction of old workings, or goofs, which may be holding largo quanti- 

 ties of inflammable gas, or water, is horizontal boring. In this work only very light 

 rods are used, as the position of the hole makes the strength of the rods a question of 

 secondary importance. The important points to consider aro the driving of the hole 

 exactly parallel with the strata, and arranging sufficient holes to render it impossible 

 for the advancing ' heading ' to come suddenly upon any old workings or narrow adits. 

 In many cases water of immense pressure has to be bored against. The ordinary 

 mode of boring is shown by fig. 194. Here the advancing head, A, may be assumed 

 to be 8 feet wide, and the minimum width of any old headings may bo taken at 4 

 feet, Supposing the pressure anticipated is such that it is only necessary to ascertain 



