122 



SEWAGE AND ITS PURIFICATION 



be produced by any system of cascades which could be applied 

 in a practical form." 



The following table summarizes some of his experiments : 



Complete analyses : 



O consumed in 

 Four Hours. 



August 9 

 August II 



3-38 



1-46 



Free and Saline 

 Ammonia. 



Albuminoid 

 Ammonia. 



1-25 



^'55 



o-i« 



Q-IO 



I may remark that the change conforms at first to what I 

 have called Stage II., the partially aerobic, in which the nitrites 

 formed increase the *' oxygen consumed." A steady reduction 

 of the carbonaceous matter then occurs from the double decom- 

 positions we have indicated, and the inception of nitrification 

 in Stage III. probably follows, though, as the nitrates are not 

 given, the point cannot be ascertained. A slight acceleration 

 is produced by forcing the air through the liquid, as against 

 simply passing over the surface of shallow layers (see 72 and 

 95 hours above), but the improvement by aeration alone for 

 four or six days is inferior to that effected by bacterial filters in 

 eight hours. The determinations, being limited to the *' oxygen 

 consumed," are not really sufficient to reveal the character or 

 amount of the purification. The third stage, in fact, includes 

 muph more than a simple process of oxidation, although it 

 demands a supply of oxygen in excess. 



