BACTERIAL PURIFICATION 239 



idea that the mechanical forcing of air into the filtering material 

 would enable the tank effluent to be applied continuously has been 

 modified by the adoption of the half-day intermittent working, and 

 this result tends to support the Dibdin process of alternate fillings." 



Waring' s System. — In 1894 a portion of the sewage of New- 

 port, R.I., w^as treated by this method of forced aeration, which 

 differs from Lowcock's mainly in the separate treatment of the 

 sludge by means of " aerators." The " combined " sewage of 

 this city became frequently mixed with sea water, the effect 

 being an increase of the suspended solids by precipitation of 

 soap and other matters, a result that has been noted in tidal 

 reaches, and has contributed to the formation of mud banks 

 and deposits. The lime and magnesia in ordinary waters do 

 not seem to secure the removal of all the higher fatty acids, as 

 a greasy scum is seen frequently in sewers. I have found the 

 soda salts of oleic and other fatty acids in solution in sewage, 

 especially that of towns with a soft-water supply, owing prob- 

 ably to the influence of the ammonia formed. These soluble 

 soaps are decomposed and precipitated by the high amount of 

 calcium and magnesium salts existing in salt water, so that the 

 sewage of Newport contained unusual amounts of soap curds. 



The sewage, after passing through a grit chamber, was 

 pumped alternately through either side of a divided tank con- 

 taining a shallow bed of broken stone to arrest the coarser 

 solids. '* The impurities in the section thrown out of use dis- 

 appeared rapidly in its interval of rest." The liquid next passed 

 slowly through four straining tanks filled with stones and 

 gravel, w^hose function was said to be " mere mechanical 

 sedimentation." As soon as these became clogged a plug was 

 drawn, and the sludge emptied into a separate " aerating tank," 

 filled with stones and gravel, where air was driven constantly 

 through the mass, and as soon as active bacterial action had 

 set in, the sludge was rapidly dissolved. Air was also forced 

 through the straining tank till it was again in condition for use. 

 This complex system is another instance of continuous working, 

 assisted by forced aeration for long periods in the hope that in 

 a given tank capacity a larger volume of sewage could be treated. 

 The action here is apparently entirely aerobic, and unaccom- 

 panied by previous hydrolysis, except what would have happened 

 in the sewers. 



Several alterations have been made in the details, and instal- 

 lations have been constructed at Willow Grove Park, Philadel- 



