476 Town Sewage. 



It appeared, however, that evidence was more plentiful in 

 regard to some divisions of the population than others, and a 

 careful consideration of the character of the results obtained in 

 these several divisions led to the conclusion, that though their 

 former estimate (10 lbs.) was probably too low, 12 lbs, was too 

 high ; and, due allowance being made for the fractional part of 

 the excreta of horses, cows, dogs, and other animals, of the 

 refuse of slaughter-houses, of soot, &c., that may reach the sewers, 

 still not more than 12^ lbs. of ammonia would be contributed 

 annually to the sewers from all sources, per head of mixed town 

 population. 



It was admitted, however, that further investigations, upon the 

 completion of the main drainage of the metropolis, were a great 

 desideratum. 



Since the publication of the Report of the Commission, in 

 March 1865, numerous gaugings and samplings of the sewage of 

 the mid and high-level sewers north of the Thames have been 

 undertaken, and many samples have been analysed by Mr, Way 

 and Dr. Odling, The results of this inquiry have not yet been 

 published ; but such information was communicated by Mr. Way as 

 enabled Dr. Gilbert to state their general bearing upon this point.* 



From these new results it appears very probable that the dry- 

 weather sewage averages only about two-thirds as much as was 

 before supposed and assumed — that is to say 40, not 60 tons, 

 per head per annum — but the average amount of ammonia 

 therein very nearly approaches to the estimate of Messrs. Hof- 

 mann and Witt (8*2 grains). 



The theoretical value of the constituents of sewage, or that 

 assignable to them when constituting a dry and portable manure, 

 is, as has been stated, obviously quite other than their realisable 

 value when distributed through an enormous volume of water. 



Assuming that the latest evidence is the most trustworthy, it 

 would seem that the earlier estimate of Messrs. Lawes and 

 Gilbert (10 lbs, per annum of ammonia) is the more correct, 

 that at Rugby too large a proportion of the rainfall had been 

 estimated to reach the sewers, and that the corrections made by 

 Lawes and Gilbert to meet the incompleteness of their records, 

 as already pointed out, were well founded. 



Composition and Value of Metropolitan Sewage at 

 different dilutions. 



To the dry-weather sewage very variable additions are made, 

 according to rainfall, &c. ; while, in time of continuous rain or 



* Both Mr. Way and Mr. Cresy frankly admit, however, that there are still 

 many open questions which materially affect the proper interpretation of the new 

 gaugings. 



