CHEMICAL ANALYSIS 



59 



of denitrification, when the effluent is admixed with other 

 water. 



The following table bears on this point :-^ 



Table of the Relation of Nitrogen to Chlorine and of 



Oxidation. 



As unoxidized nitrogen is a constituent of the more 

 dangerous kinds of natural pollution, the ratio between the 

 different forms of nitrogen furnishes more useful information 

 than a mere consideration of its amount, since nitrogen com- 

 pounds when oxidized are harmless, but when unoxidized are 

 liable to occasion smells, and to be in other respects deleterious. 

 A certain quantity of N is lost as gas during the changes, but 

 the residue will give a minimum measurement of the original 

 sewage strength. The proportion between the oxidized and 

 unoxidized N will then denote the extent to which the sample 

 has been purified. A judgment can therefore be formed from 

 the sample without an analysis of the original sewage, as the 

 chlorine contents also give a clue to the strength, and thus 

 such a method has an advantage over the ordinary system of 

 calculating sewage purification, as it obviates the difficulty of 

 obtaining conformable samples. It is useful also to make a 

 correction to a standard chlorine value in comparing the 



^ Phelps has drawn up a table showing the application of this formula to 

 American Sewages {American Technology Quarterly, March and June, 1905). 



