318 



MINING 



by filling it partly with tenacious clay, and then driving into it a tapering iron 

 rod, -which nearly fills its calibre, called the claying-bar (Jig. 1482). This being forced in 



1480 



J481 



1482 



1479 



1483 



1484 



1485 



with great violence, condenses the clay into all the crevices of the rock, and secures the 



dryaess of the hole. When the hole 

 1486 is dry, and the charge of powder in- 



troduced, the nail, a small taper rod 

 of copper, is inserted so as to reach 

 the bottom of the hole, which is now 

 ready for tamping. Different sub- 

 stances are employed for tamping, 

 or cramming the hole, the most usual 

 one being any soft species of rock 

 free from siliceous or flinty particles. 

 Small quantities of it only are intro- 

 duced at a time, and rammed very 

 hard by the tamping-bar, which is 

 held steadily bygone man, and struck 

 with a sledge by another. The hole 

 being thus filled, the nail is withdrawn by putting a bar through its eye, and striking 

 it upwards. Thus a small perforation or vent is left for the safety-fuse which com- 

 municates the fire. 



For conveying the fire, the large and long green rushes which grow in marshy 

 ground were formerly used in our mines, and are still used in some quarries. A slit is 

 made in one side of the rush, along which the sharp end of a bit of stick is drawn, 

 so as to extract the pith, when the skin of the rush closes again by its own elasticity. 

 This tube is filled up with gunpowder, dropped into the vent-hole, and made ready 

 with a bit of clay. A paper smift, adjusted to burn a proper time, is then fixed to 

 the top of the rush-tube, and kindled, when the men of the quarry retire to a safe 

 distance. The ' safety-fuse ' is now, however, almost universally employed. 



In fig. 1486 the portion of the rock which would be dislodged by the explosion is 

 that included between A and B. The charge of powder is included in that part 



1487 



1488 



which fills the hole up to c ; from which point to tho top, the hole is filled with 

 tamping. The old smift is shown at D. 



