Tile Purificatio7i of Seivagc. 



205 



impurity is suspended and will settle out by itself, and, 

 therefore, no treatment by land or otherwise should be 

 credited with this part of the purification. Irrigation 

 removed 62^ of the soluble albuminoid matters, precipi- 

 tation by iron removed 73%, whilst precipitation and 

 irrigation together removed the large amount of 81 per 

 cent, the irrigation effluent itself being improved 70%. 



Table IV. 

 Results of Treatment of the Sewage of Astley Bridge, near Bolton 

 (180,000 gallons per day) unth Basic Persulphate of Iron at 

 the rate of one ton per niillion gallons, together ivith J cwt. of 

 lime per million gallons. 



