XVI. 



J. M. SMAIL. 



York. 

 Cobbles and gravel graded 

 Fine river sand ... 



Total 



2 feet 6 inches 



4 „ „ 



6 



G 



Average rate of filtration 1 gallon per square foot per hour. 



The low rate of filtration is explained by the engineer as 

 being considered advisable by the company in order to 

 secure water of undoubted purity. Considering the source 

 of supply, river Ouse, I can quite understand the feelings 

 of the company and their engineer. A recent bacterio- 

 logical examination winch will be referred to further on, 

 is quite in accord with the rate of filtration carried out. 



In connection with the composition of slow filter beds on 

 the Continent and America, Professor Mason gives the 

 following information : — 





Berlin. 



Warsaw. 





Ft. In. 



Ft. Iq. 



Fine sand 



,.. 1 10 



... 2 



Coarse sand ... 



... 2 





Fine gravel 



... 6 



... 2 



Medium gravel 



... 5 





Coarse gravel... 



... 3 



... 3 



Small stones ... 



... 4 



... 1 



Large stones ... 



... 1 



... 11 



Total 



... 4 G 



... 4 4 





Zurich. 



Hague. 



Fine sand 



... 2 8 



... 1 



Coarse sand ... 



... 6 



... 10 



Fine gravel ... 



... 4 





Coarse gravel 



... G 



... 10 (sea shells) 



Large stones ... 







... 6 



Total 



4 



3 2 



