SUBSIDENCE 



151 



ishould be in duplicate, and some have been made with sharp 

 edges to cut up the organic matter. 



Grease, which is often a great difficulty, may be intercepted 

 by grease-traps, or it may be broken up into an emulsion with 

 lime or other materials for subsequent treatment. The 



methods used at Bradford and other towns will be described in 

 Chapter XIV. Grease from ordinary soap-suds does not seem 

 to admit of profitable extraction, as the fat is so much con- 

 g^ taminated. 



IH The amount of suspended matter in sewage is greatly 

 [■influenced by its history before arrival at the works. Where 



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