618 Adeney — Dissolved Gases and Fermentative Changes. 



It is otherwise with the second-stage fermentation of a polluted water, since 

 this stage of fermentation ^^I'obably does not proceed so rapidly in a water 

 exposed to the same conditions as the diffusion of atmospheric oxygen into it, and 

 since, if it does, secondary products of a poisonous nature, such as are formed 

 during putrefaction, cannot be similtaneously formed with nitrous or nitric acid 

 from the very nature of the process of nitrification. 



It is right, therefore, in dealing with the question of the pollution of a water- 

 course, to make this distinction between the oxygen required for the first stage 

 fermentation and that required for the second stage. 



I have made these remarks more particularly with the view of drawing 

 attention to the possibility which the method of observation I have employed in 

 this investigation presents, of formulating definite standards of impurity which 

 should be allowed in the case of drainage waters discharged into a watercourse ; 

 it being possible, it should be observed, to formulate a standard according to local 

 conditions and requirements. 



A simple standard, which Local and River Conservancy Boards could control, 

 could be framed as follows : — 



The limit of impurity to be allowed to a given water to be such, that, when a 

 given volume of it is mixed with a given volume of tap- or other good water, and 

 the mixture kept in a bottle out of contact with air, under the conditions I have 

 described, for a sufficient length of time, a decided oxidation of the ammonia 

 originally present in the mixture into nitrous, or nitric, acid shall be indicated. 



This is, howeover, merely a suggestion. Were the principle of the proposed 

 standards adopted, experience would show how best to formulate them. 



General Conclusions. 



The following conclusions may be drawn from the experiments recorded in 

 this Paper : — 



1. That the method and apparatus described in the Paper for preserving 

 natural waters, or artificial solutions, out of contact with air, and for analysing 

 the gases in solution in them, before and after keeping, are capable of yielding 

 very accurate results, and that the method is not attended with any great 

 experimental difficulties. 



2. That observations of the changes in composition of the gases in solution, 

 which take place during the course of fermentation in the presence of mixed 

 organisms, under the conditions described, when made in conjunction with an 

 examination of the changes which simultaneously occur in the organic and 

 inorganic nitrogenous bodies in the water, are productive of extremely important 

 results, and are necessary if it be desired to investigate completely the chemical 

 changes which accompany such fermentations. 



