BORING 



443 



water as hereafter described. As the drill passes into the rock, cutting an annular 

 channel, the portion of stone, encircled by this channel is, when of a compact nature, 

 undisturbed, and the drill rod passing down over it preserves it intact until the solid 

 cylindrical core thus formed is withdrawn with the rods. 



The diamonds are placed at intervals of about ^rd of an inch apart both inside and 

 outside the tube, the projection beyond the surface of the metal being not more than 

 ^jth of an inch. 



The diamond teeth are the only parts of the tool which come in contact with the 

 rock, and their hardness is such that more than 2,000 feet have been drilled by the 

 same points with but little appreciable wear. 



The drill rods are made hollow, in order that a volume of water may be conducted 



to the boring bit, at once moistening the rock, washing the cuttings away, and 

 preventing the over heating of the diamonds. 



The machinery for boring great depths is shown by jig. 180, p. 442, and consists of 

 a portable engine having two oscillating 6-inch cylinders with a 6-inch stroke. The 

 boiler is tubular, 3 feet x 7 feet, and with flues 3 inches in diameter, the steam 

 capacity being about 16 H. p. 



The pump p and water hose H are connected by rubber hose with any convenient 

 stream or^ reservoir of water, and also with the outer end of the drill pipe by similar 

 hose having a swivel joint. Through this hose a stream of water is forced, by M. 

 Fauvelle's system, into the hollow drill rod, from which it only escapes at the bottom 

 of the diamond pointed bit. 



_ The drill rods may be extended to any desirable length by simply adding fresh 

 pieces of tubing. The successive lengths are quickly coupled together by an inside 

 coupling 4 inches long, the drill being held firmly in its place by the chuck o at the 

 bottom of the screw shaft. 



The speed of drilling depends chiefly of course upon the character of rock met with : 

 in ordinary rock the drill being fed at the rate of 300 revolutions to the inch 

 the diamonds cutting the one three-hundredth part of an inch at each revolution, and 

 in marble, hard sandstone, &c., at the rate of an inch for every 200 revolutions. 



The progress of the diamond bit or crown does not depend upon the pressure of the 



