118 



A. Pedler— Om flie past anH present 



[No. 2, 



been contaminated with sewage matters will entirely purify itself in a flow 

 of a few miles, and will thus again become fit for potable and domestic 

 purposes. The weight of the evidence appears however to disprove this 

 statement, and further experiments made by Dr. Frankland have shown 

 that this oxidation of sewage matter when present in running water is a 

 process of extreme slowness. Thus in the report of the Rivers Pollution 

 Commissioners, he writes : 



" Assuming, however, that if the polluted water had been constantly 

 exposed to the air, a portion at least of the oxj^gen used would have been 

 replaced, and assuming further that the oxidation proceeded during 16S 

 hours at the maximum rate observed, then at the end of that time, only 

 62'3 per cent, of the sewage would be oxidized. 



" It is thus evident that so far from sewage mixed with 20 times its 

 volume of water being oxidized during a flow of 10 or 12 miles, scarcely 

 two-thirds of it would be so destroyed in a flow of 168 miles, at the rate 

 of one mile per hour, or after the lajDse of a week. But even this result 

 is arrived at by a series of assumptions w?hich are all greatly in favour of 

 the eSiciency of the oxidizing process. Thus, for instance, it is assumed 

 that 62'3 per cent, of sewage is thoroughly oxidized, and converted into 

 inofEensive inorganic matter, but the experiments showed that, in fact, no 

 sewage matter whatever was converted or desti*oyed even after the lapse 

 of a week, since the amount of carbonic acid dissolved in the water 

 remained constant during the whole period of the experiment, whilst, if the 

 sewage had been converted into inorganic compounds, the carbonic acid, as 

 one of these compounds, must liave increased in quantity. 



" Thus, whether we examine the organic pollution of a river at dif- 

 ferent points of its flow, or the rate of disappearance of the organic matter 

 of sewage when the latter is mixed with fresh water, and violently agitated 

 in contact with air, or finally, the rate at which dissolved oxygen disappears 

 in water polluted with 5 per cent, of sewage, we are led in each case to the 

 inevitable conclusion, that the oxidation of the organic matter in sewage 

 proceeds with extreme slowness, even when the sewage is mixed with a 

 large volume of unpolluted water, and that it is impossible to say how far 

 such water must flow before the sewage matter becomes thoroughly oxidized. 

 It will be safe to infer, however, from the above results, that there is no 

 river in the United Kingdom long enough to effect the destruction of 

 sewage by oxidation." 



Thus Dr. Frankland is of opinion that a river water once largely 

 contaminated with sewage or organic matter can never of itself become 

 sufficiently pure again to be a safe water supply. To this point I shall 

 again have occasion to refer, when speaking of the proposed sources of the 

 new supply. 



