THE MINERAL DEPTHS 



for operating such reciprocating drills presents no 

 mechanical difficulties, and the fact that power of this 

 kind can be transmitted long distances by the use of 

 flexible tubes made such drills popular for several 

 years. But the cost of operating such drills is so 

 much greater than that of the new electric drills that they 

 are rapidly being replaced in mining work. 



The first attempts to produce an electric drill with 

 a reciprocating motion were so unsuccessful that in- 

 ventors turned their attention to perfecting some ro- 

 tary device. This proved more successful, and rotary 

 drills, operating long augers and acting like ordinary 

 wood-boring machines, are now used extensively 

 for certain kinds of drilling. The more recent forms 

 perform the same amount of work as the air drill, 

 with a consumption of about one-tenth the power. 

 Moreover, none of the energy is lost at high altitudes 

 as in the case of air drills, and they are not affected by 

 low temperatures which sometimes render the air 

 drill inoperable. On the other hand, the air drill is 

 a hardy implement, capable of withstanding very rough 

 usage, whereas the electric drill is probably the more 

 economical, as well as the more convenient drill of 

 the two. 



In certain kinds of mining, such as in the potash 

 mines of Europe and the coal mines of America, these 

 electric drills operating their long augers have been 

 found particularly useful. The ordinary type of drill 

 is so arranged that it can be operated at any angle, 

 vertically or horizontally. The lighter forms are 

 mounted on upright stands, with screws at the ends 



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