PROCEEDINGS OF THE COTTESWOLD CLUB I33 



artificial filters docs not depend upon the thickness of 

 the filter, hut uj)on the formation upon its surface of a 

 slimy mud, which is deposited from the water, and which 

 is loaded with bacteria. The purification of the water is 

 mainlv eflccted in passing through this layer by a vital 

 rather than by a physical process, although by stopping 

 up the pores of the filter it also increases the straining 

 effect and so prevents the bacteria from passing. By a 

 vital process is meant the fermentative effect of the bacteria 

 in the slimy layer upon the organic matter in the water 

 causing its destruction, or reduction to harmless products. 

 There are several patented processes for the purifying 

 of water on a large scale by special means, they mostly 

 comprise the use of iron in one form or another, the 

 several compounds recommended being stated to greatly 

 aid the purification of water by filtration. One such com- 

 pound is termed polarite, and another magnetic iron carbide. 

 A third process, and one the use of which appears to be 

 extending, is the agitation of the water with pieces of 

 metallic iron by allowing the water to flow through a 

 revolving cylinder containing the pieces of iron, such as 

 iron punchings or any small pieces of the metal, which 

 are caused to fall through and through the water as the 

 cylinder revolves. A small portion of iron is taken up 

 as carbonate, and on after exposure to the air is precipi- 

 tated as oxide, carrying with it some of the impurity of 

 the water, which along with the iron is then removed by 

 filtration. Dr Swete, the Worcestershire Analyst, 

 strongly advocates the process after given it an extended 

 trial. By the careful management of ordinary sand filters 

 however such excellent results are obtained as to allow 

 of any extra process being dispensed with. 



The Danger of Drinking Polluted Water 

 with examples 



Ample evidence has been obtained to prove that 

 drinking water may become the medium for the conveyance 

 I 



