EXCAVATING THE RAW MATERIALS. 



377 



comprise the pump-tanks, air-compressor, automatic switch, and piping. 

 There are no floats. There are no air-valves outside the engine-room. 



"The air is not allowed to escape after doing its work. The expan- 

 sive force of the air is used in the compression cylinder of the com- 

 pressor, thus giving back the greater part of its energy to the compressor. 



"Suppose the compressor to be in operation with switch set as in 



--^T-^-T: Water Supply 

 FIG. 81. Harris system of marl-pumping. 



the figure, the air will be drawn out of the right-hand tank and forced 

 into the left-hand tank, and in so doing will draw marl into the former 

 and force it out of the latter. 



"The charge of air in the system is so adjusted that when one tank 

 is emptied the other is. just filled. At that moment the switch will 

 reverse the pipe connections so that action in the tanks will be reversed. 



"The switch is adjustable and can be set or regulated while the 

 pump is in operation." 



For further data, reference should be made to a paper by E. G. 

 Harris, published in "Mines and Minerals," vol. 15, pp. 513-514. May, 

 1905. 



