WATER FILTRATION. XVII. 





Airn 



3rica. 









Hudson 



, N.Y. 



Ploughkeepsie 





Ft. 



In. 





Ft. 



In. 



Fine sand ... 



... 



G 





2 







Coarse sand 



... 1 



6 









Fine gravel... 



... 



6 





... 





Medium gravel 



... 



6 





1 



6 



Coarse gravel 



... 



6 





... 





Small stones 



... 



6 









6 



Large stones 



... 2 









2 







Total ... 



... 6 









6 







Australia.— 



-Hunter 



River Water Supply. 



Sand... 



... 



... 



3 feet inches 



Gravel 



Total 



::: 







„ 6 







3 



,, 6 





With the exception of Liverpool and Edinburgh, which 

 are supplied with water from moorlands, the foregoing 

 may be taken as typical cases dealing with water obtained 

 from rivers. 



In dealing with river waters it has been found conducive 

 to efficient filtration to adopt sedimentation in storage 

 reservoirs, or the use of coagulents, sulphate of alumina or 

 lime. The advantages of sedimentation cannot be over- 

 looked. A few days rest will effect the clarification of 

 river waters containing all but the finest particles, and the 

 deposition of mineral matter in suspension results in a con- 

 siderable reduction of bacteria present. In connection 

 with the matter, Dr. Frankland has published the following 

 figures in relation to some of his investigations of the 

 London Water Supply. Samples taken from the West 

 Middlesex Works at Barnes, gave the following results : — 



Bacteria per cc. 



Unfiltered Thames water from Hampton ... 1,437 

 Unfiltered water after passing through one 



subsiding reservoir ... ... ... 318 



2-J'i!y21, 190 1. 



