1 ACAVATINt; MACIUNKS AN!) l:iflv IMilLLS 21 



Power Drills. When the conditions are such that use can 

 l>e made of them, it is nearly always preferable to use jxmer 

 drills, on account of their greater speed of penetration and 

 -T'-ater economy of work. Power drills are worked by direct 

 steam pressure, or by compressed air generated by steam or 

 water power, and stored in receivers from which it is led to the 

 drills through iron pipes. A. great variety of forms of power 

 drills are available for tunnel work in rock, but they can nearly 

 all be grouped in one of two classes: (1) Percussion drills, and 

 (2) Rotary drills. 



Percussion Drills. The first American percussion drill 

 was patented by Mr. J. J. Couch of Philadelphia, Penn., in 

 March, 1849. In May of the same year, Mr. Joseph W. Fowle, 

 who had assisted Mr. Couch in developing his drill, patented a 

 percussion drill of his own invention. The Fowle drill was 

 taken up and improved by Mr. Charles Burleigh, and was first 

 used on the Hoosac tunnel. In Europe Mr. Cav6 patented 

 a percussion drill in France in October, 1851. This invention 

 was soon followed by several others ; but it was not until Som- 

 meiller's drill, patented in 1857 and perfected in 1861, was used 

 on the Mont Cenis tunnel, that the problem of the percussion 

 drill was practically solved abroad. Since this time numer- 

 ous percussion drill patents have been taken out in both 

 America and Europe. 



A percussion drill consists of a cylinder, in which worl 

 piston carrying a long piston rod, and which is supported in 

 such a manner that the drill clanijed to the end of tin- piston 

 rod alternately strikes and is withdrawn from the rock as the 

 ID reciprocates back and forth in the cylinder. Means are 

 devised by which the j.istuii rod and drill turn slightly on their 

 axis alter each stroke, and also by which the drill is fed for- 

 ward or advanced as the depth of the drill-hole increases. 

 The drills of this type which are in most common use in 

 America are the Ingersoll-Ser^eant and the IJ.-md. Thereare 

 various other makes in common use. however, which differ 



