46 SMALL WATER SUPPLIES. 



care in handling, as a heavy blow may explode them 

 at the wrong time, and no electrical connexion of 

 any sort should be made before the whole affair 

 is let down into the bore-hole ready for exploding. 

 Nitro-glycerine for the purpose is bought in water- 

 proof cartridges, which must be kept dry and cool, 

 and above all away from frost. They are placed in 

 the torpedo, and the topmost into which the detonator 

 is pushed constitutes the primer. The whole may 

 then be exploded, the water in the bore-hole being 

 a sufficient tamping, as it is called, without further 

 trouble. The number to be used for any particular 

 rock will generally be stated by the firm who supply 

 the explosive. 



