BACTERIAL PURIFICATION 225 



was stated that if the " double contact " did not suffice, they 

 would employ a " third contact." This triple treatment was 

 adopted at the Hampton Sewage Works in the beginning of 

 1899, and also at Lincoln and elsewhere. 



In America it is recognised that intermittent filtration is 

 much more expensive than was formerly anticipated. The 

 filters constructed in New England a few years ago are one by 

 one becoming clogged and inoperative except at very low rates, 

 and it is now evident that they necessitate heavy maintenance 

 charges. 



15 



