56 
PURIFICATIOX AXD DISPOSAL OF SEWAGE. 
1. Dilution. 
This method is allowable for cities situated on the sea or ou rivers whose flow is 
very large as compared with the sewage (100:1) and the unfiltered water of which 
is not used as a water supply. 
2. Sewage farming. 
3. Chemical precipitation. 
4. Intermittent filtration. 
Needs sandy soil. 
5. Septic tank. 
6. Contact bed treatment. 
7. Continuous filtration: 
a. Scott-Moncrieff system. 
b. The Ducat. 
c. Whitaker & Bryant. 
d. F. Stoddart. 
e. G. Salford. 
