EXCAVATING MACHINES AtfD KOCK DltlLLS 31 



The quantity of explosives required for blasting depends 

 upon the quality of the rock, since the force of the explosives 

 must overcome the cohesion of the rock, which varies with its 

 nature, and often differs greatly in rocks of the same kind and 

 composition. The quantity of explosives required to semiv 

 the greatest efficiency in blasting any particular rock may bv 

 determined experimentally, but in practice it is usually di-dm -<-d 

 by the following rules: (1) The blasting force is directly pro- 

 portional to the weight of th- explosives used, and (2) the bulk 

 of the blasted rock is proportional to the cube of the depth of 

 the holes. It is usually assumed, also, that the explosive 

 should fill at least one-fourth the depth of the hole. 



