58 SEWAGE AND ITS PURIFICATION 



the albuminoid ammonia process was introduced it was well 

 known that there was a varying relation between the quantities 

 of albuminoid ammonia and the amount of organic nitrogenous 

 matter. Too much importance must not, therefore, be placed 

 on this item of the analysis. 



An effluent that is in an active state of wholesome bacterial 

 change, in presence of free and potential oxygen, will conform 

 to Adeney's proposed test : *' The limit of impurity to be 

 allowed in a water should be such that when a given volume 

 of it is mixed with a given volume of fully aerated river water, 

 and the mixture kept out of contact with air, a decided oxida- 

 tion of the ammonia originally present into nitrous or nitric 

 acid shall be indicated." It will be seen that this proposal is 

 practically an incubation test, and the result obtained by it 

 should be similar to those given by the incubator test already 

 described. 



Ratio of the Chlorine to the Total Nitrogen. 



In perfectly fresh excreta, taking the solids and liquids 

 together, the total nitrogen somewhat exceeds the chlorine. 

 This proportion will remain unchanged when diluted with 

 water containing only the ordinary small amount of chlorine, 

 as long as the nitrogen remains in fixed forms. Therefore the 

 ratio is applicable to fresh sewages generally, independent of 

 dilution, but will be immediately altered by the production of 

 gas. Let CI and N be the parts of chlorine and nitrogen 

 respectively, the " residual ratio " will be — 



N X loo 



R = 



CI 



or, in cases of great dilution, with a high chlorine W in the 

 water-supply, 



N X loo 



R 



Cl-W 



The simpler formula is usually sufficient. In the original 

 excreta the number R will be somewhat over 200, in fairly 

 fresh sewage it will be about 100; in bacterial effluents, on the 

 other hand, the fall of R will indicate the gaseous dispersal 

 of nitrogen. With chemical or mechanical treatment R will 

 fall, owing to the abstraction of matter as sludge. Where 

 heavy nitrification has been the main feature there may be 

 little or no fall, this afterwards occurring rapidly in the process 



