CHEMICAL CHANGES 



131 



altered the composition in a favourable sense. It is therefore 

 desirable, wherever possible, to analyse an effluent within a 

 very brief time from its collection, and the more important 

 determinations should be made on the spot within a few 

 minutes of the discharge. Although this is undoubtedly the 

 only fair procedure, such analyses are not, of course, comparable 

 with those carried out under the usual conditions, which give 

 an apparently higher quality to the effluent, but they demon- 

 strate the existence of the rapid and beneficial improvement 

 in some effluents which I consider, with Adeney, one of the 

 main criteria of safety. 



Typical Examples of the Oxygen Relations. 

 Parts per 100,000. 



[Wembley sewage farm 



! effluent, 1896 



I Croydon sewage farm 



I effluent, 1895 



I River Brent, polluted, 



I 1896 



I Precipitation and coke- 

 breeze filter, Dibdin, 



, 1894 



[Tank effluents: 



Exeter, 1896 



Ashtead, 1898 ... 



Caterham, 1899 ... 

 I Coarse bed, Sutton, 1899 

 [Filtrates (final effluent) 

 averages : 



Exeter, 1897 



Ashtead, 1898 ... 



Caterham, 1899 ... 



Sutton, 1899 





< > 

 53 



2-14 

 2*51 

 00 



— o'577 



0*117 

 0-343 



2*41 



0-03 !o-o5ili8-45 

 o -34610 -59 I26-33 

 0-10810-184' 9*69 



-29 



2-32 0-0 



1-04 



4 '32 



o'55 



0*027 

 9-84 0-035 

 9-25! o-o 



1-46 1-65 



0-966! 3-53 



0-60930-0 

 2-71 97 

 0-83. 11-7 



2-32 



0-46 



48-7 

 63-0 

 00 



i-o 



1*0 



trace 



27-0 



33-0 

 91-6 

 62-0 

 82-0 



9—2 



