202 Mr. Harry Grimshaw oii 



body retains the noxious sulphur compounds, and also acts as 

 a carrier of oxygen to the organic matter, which it therefore 

 tends to destroy by a slow process of combustion. That 

 the moist peroxide of iron has this property has been long 

 known to chemists'*. It would appear that the basic 

 sulphate of iron fulfils remarkably well the various require- 

 ments of a precipitant for sewage, which may be said 



to be : — 



1. Immediate combination with the organic matter of 



the sewage. 



2. Rapid subsidence of precipitate so formed. 



3. Power to combine with the sulphur compounds. 



4. No tendency to rob the sewage of dissolved oxygen. 



5. Powers of oxidation on the organic matter of the sludge. 



6. The property of leaving the effluent in a good con- 

 dition for nitrification to take place during or after filtration. 



7. Little addition to weight of sludge. 



8. Cheapness. 



Below are tables of results of analyses of sewage and 

 waste waters from manufactories which have been treated 

 with this latest development of the iron process at Salford, 

 Derby, Burton, Nuneaton, Astley Bridge, etc. After 

 seeing the results of experimental working at the Salford 

 Sewage Works, that Corporation have decided to apply 

 the basic-iron process to the whole of the sewage. 



Average percentage purification at Salford treating 

 100,000 gallons per day for about 4 months : — Precipitation 

 only, 55 per cent; with sand filter, 68 per cent; with 



•"Thorpe's Chemistry," Vol. II., p. 376. "Ferric hydrate is reduced 

 by organic matter in process of decomposition, but in contact with air it is 

 quickly reoxidized, and it thus acts as a carrier of oxygen from the air to the 

 organic matter, and greatly promotes its decomposition. The rapid decom- 

 position of human and woody fibre in many ferruginous soils is thus brought 

 about." 



"Watts' Dictionary of Chemistry," Vol. III., p. 58. " In contact with de- 

 caying organic matter the ferric hydrates part with oxygen, but take it up again 

 on exposure to air." 



