BORNITE 



450 



boring bar f-inch diameter, when sharpened, will cut a hole 1 inch to 1 th inch 

 diameter. 



Figs. 199, 200, 201 show chisel-point borers; Jig. 202 a crown borer; and fig. 203 

 a Z borer. 



The rate of hand-boring must necessarily depend on the workman, quality of steel, 

 and hardness of rock, also on other minor circumstances. In a shaft 9 x 5J feet 

 nine men sunk 15 feet in a period of 26 days of twenty-four hours per day. Tho 

 average number of holes ij inch diameter bored per shift of eight hours was 3, 

 average depth of each hole 2 feet. During the run of 78 shifts the aggregate depth 

 of the various holes was 468 feet ; total cost of removing the ground, 111. Tho 

 average weight of rock removed per blast was 3 cwts. In another shaft the rate of 

 boring per minute, one man striking, was '17 inch, two men striking '25 inch. Tho 

 number of blows required for a hole 30 inches deep was 4,500, number of borers 

 blunted 7 ; depth bored per borer 4 inches. In machine-boring the progress varies 

 chiefly with the rapidity of the blow and toughness of the rock, or from to 6 inches 

 per minute. 



The boring machines employed in underground work are best driven by compressed 



199 



201 



202 



203 



air. The air-pumps should be well constructed ; and the pistons or rams worked in 

 connection with water, with the double object of keeping down the temperature of the 

 air, and expelling into the receiver a volume equal to the cubic contents of the air- 

 pump stroke. Jordan's compressor is a cheap and well-contrived apparatus. Low has 

 also devised an efficient pump ; while Ford of Melbourne, and Angstrom of Sweden, 

 have produced simple and effective pumps worked in combination with ordinary pump 

 rods. 



In order to obtain the full effect of boring machines, the stuff must bo removed 

 rapidly after each blast. This object can only be accomplished by employing pneu- 

 matic tackles in connection with underground sinks, and having good forwarding ways. 

 The advantages of using machine-borers in mining operations are (1) Decided 

 economy of time and money ; (2) Diminution of the number of skilled miners, who 

 can be advantageously employed in other parts of the mine ; (3) Excellent venti- 

 lation of shafts, sinks, and levels ; (4) Possibility of making the roof, floor, and 

 sides of a level more regular than can be effected by hand-boring; (5) Kate of 

 driving levels or sinking shafts two to four times greater than is practicable by hand- 

 boring. 



BORXflNE. See TETRADYMITE, OR TEIXTTRIC BISMUTH. 



BORNXTi:. Purple copper ore or Bunt Kupfererz. See COPPER. 



It is to be regretted that names so similar as Bornine and Somite, both compli- 

 mentary to Von Born, should have been bestowed upon widely different minerals, 



