368 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



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StCIIOHAl ILCVATION 



Figure 1. — Dorr^sifeedsedimentation^tank. 



tanks (fig. 2) consists of a series of wooden flights or squeegees, the 

 ends of which are connected by two endless chains. The flights rest 

 on the bottom of the tank; and as they are moved by motor-driven 

 sprockets, they scrape the sludge to one end of the tank. There are 

 various other mechanical methods of removing sludge from sedimenta- 

 tion tanks, which are modifications or refinements of the two above 

 mentioned. 



