CHAS. E. FOWLER. 275 



adelphia, "consists in great part in the conversion of 

 the iron into ferrous carbonate (proto carbonate of iron) 

 through the agency of the carbonic acid, which partly 

 dissolves in the water and partly remains suspended in 

 the form of dark green turbidity. On exposure to the 

 air the iron is converted into ferric hydroxide (hydrated 

 sesqui-oxide of iron) which, settling rapidly, carries down 

 with it and oxidizes the organic matter. ***** 

 In addition to the above chemical effect it is probable 

 that in some waters, e. g., those containing much dis- 

 solved organic matter, a direct oxidation of this occurs 

 at the same time that the iron is acted upon, with the re- 

 sult that the iron salts of organic acids are developed 

 and these are subsequently thoroughly oxidized when 

 exposed to the air." Efforts have been made to put this 

 aid to sedimentation in use in one or two places in this 

 country. 



One method of operation is to cause the water to be 

 treated to pass longitudinally through one or more iron 

 cylinders which revolve slowly. 



Attached to the inner jDeriphery of these cylinders are 

 shelves. A quantity of cast iron borings or wrought iron 

 plate punchings are placed in the cylinders. As these 

 revolve the shelves take up the fragments of iron and 

 shower them down through the water in its passage 

 through the cylinders. 



The diameter and length of the cylinders are so pro- 

 portioned as to give the necessary length of contact be- 

 tween the water and the iron. The constant attrition of 

 the fragments of iron keep their surfaces bright, and 

 thus in the best condition for being dissolved by the 

 water. Some method of aeration is used in connection 

 with this process to hasten the oxidation of the dissolved 

 iron. After passing through the cylinders and the aerat- 

 ing device, the water is delivered to the settling basins 

 where it is allowed to stand until claritied. This method 



213 



