44 



SMALL WATER SUPPLIES. 



of being crushed unless some form of slide joint is 

 introduced. A good form is shown by fig. 35, and it 

 divides the rod into two sections. The upper por- 

 tion is counterbalanced by a weighted lever, which 

 allows of the lower section only acting by percussion. 

 As will be seen from the figure the two parts slide 

 over each other, and so as the top part is counter- 



n 



Plan, 





FIG. 35. 



FIG. 36. 



FIG. 37. 



balanced it only drops slowly, while the bottom 

 section, having the full force of gravity upon it, will 

 do the striking hit only with a force equal to the 

 weight of the lower section. The limit of travel of 

 the slide is generally about 12 in., and the most satis- 

 factory load for the bottom or striking section is 

 15 cwt. A slide joint is not required for rotary 

 drilling. Percussion tools have already been illus- 



