208 MICRO-ORaANISMS IN WATER 



Ferric salts. — Ferric salts were next investigated,, 

 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 lbs. 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.e. 



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



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



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



„ „ „ „ and 500 lbs. 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 lbs. of ferric oxide per million gallons of sewage 223,432 



200 „ „ „ „ „ 204,508 



300 „ „ „ „ „ 130,118 



400 „ „ „ „ „ 66,528 



300 „ and 1,000 lbs. of lime per million 



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



300 lbs. of ferric oxide and 1,000 lbs. 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 : — 



