208 MICRO-ORGANISMS IN WATER 



Ferric salts. Ferric salts were next investigated r 

 both alone and when used in conjunction with lime. 

 The following tables show the results obtained : 



Bacterial purification of Sewage with different amounts of Ferric 

 Sulphate with and without Lime 



Series A 



Number of 

 bacteria in 1 c.c. 



Original sewage .......... 218,960 



Ditto after settling 1 hour without additions .... 132,480 



Ferric oxide 



Effluent with 200 Ibs. per million gallons of sewage . . . 30,442 



,, and 400 Ibs.of lime per million gallons of sewage 49,025 



800 . 22,000 



400 . 6,080 



500 . 9,800 



1,000 ., . 8,940 



Series B 



Number of 

 bacteria in 1 c.c, 



Original .sewage 218,960 



Ditto, after settling 1 hour without additions .... 132,480 

 Effluent with 400 Ibs. of ferric oxide per million gallons of sewage 6,080 

 ,, ,, and 500 Ibs. of lime per million 



gallons of sewage 9,800 

 1,000 8,940 



Series C 



Number of 

 bacteria in 1 c.c. 



Original sewage 1,398,600 



Ditto after settling for 1 hour without additions . . . 970,000 

 Effluent with 100 Ibs. of ferric oxide per million gallons of sewage 223,432 

 200 204,508 



300 130,118 



400 66,528 



300 and 1,000 Ibs. of lime per million 

 gallons of sewage ; lime mixed with sewage first 176,904 

 300 Ibs. of ferric oxide and 1,000 Ibs. of lime per 

 million gallons of sewage ; ferric oxide mixed 

 with sewage first 46,445 



Alum. The action of aluminium sulphate, or crude 

 alum, was next tried alone and in conjunction with lime,, 

 with the following results : 



