I>UEIFICATION OF WATER FOR DRINKING PURPOSES 207 



Series B. — Different proportions of Copperas with the corresponding 



proportions of Lime 



Number of 

 bacteria in 1 c.c. 



322,400 



271,400 



20,620 

 16,640 

 7,370 

 9,204 

 6,972 

 1,269 



In both the above series of experiments the lime was 

 added to the sewage first, and thoroughly incorporated 

 with it before the addition of the copperas. 



In order to see if a better result could be obtained 

 by mixing the sewage with the copperas first, and then 

 adding the lime, or if as good a result could be obtained 

 by precipitating the copperas with lime, and adding the 

 precipitated ferrous hydrate to the sewage, the follow- 

 ing experiments were made : — 



Bacterial purification of Seioage with the same amoimts of 

 Copperas and Lime added in different ways 



Number of 

 bacteria in 1 c.c. 



Original sewage 507,800 



Ditto after settling 1 hour without additions .... 422,400 



Effluent with 500 lbs. of copperas and 650 lbs. of lime per million 



gallons of sewage ; copperas added first .... 15,950 



Ditto, lime added first 15,800 



Effluent with 1,000 lbs. of copperas and 300 lbs. of lime per 



million gallons of sewage ; lime and copperas added 



together 9,476 



Effluent with 1,000 lbs. of copperas and 800 lbs. of Hme per 



miUion gallons of sewage ; lime and copperas added 



together 12,576 



Ditto, copperas added first 9,944 



Ditto, lime „ » 10,406 



^ It should be noted that in this sewage 500 lbs. of lime were required 

 to combine with the free carbonic acid, whilst the additional quantity of 

 lime employed corresponds to the sulphuric acid in the copperas added, 

 and thus serves to decompose the latter. 



