Toicn Sewage. 



477 



storm, some water passes at once into the Thames. The total 

 amount issuing from the sewers averages somewhere about 80 tons, 

 and pretty certainly not more than 100 tons per head per annum ; 

 twice or twice and a half as much as the most recently estimated 

 dry-weatlier flow. 



The dilution is of course increased, and the value of the 

 contents diminished to the same extent as the bulk is aug- 

 mented, as the following Table shows : — 



Table IV. — Amount and Value of Sewa:-re at different Dilutions. 



80 tons of sewage to 12^ lbs. of ammonia would be equivalent 

 to nearly 5 grains per gallon, value l'25d. for the constituents in 

 1 ton; or 100 tons, to less than 4 grains, value Id. 



Since we are now discussing the tlteoretical value of sewage, a 

 comparison with Peruvian guano may be useful, both to give 

 a definite idea of the extent of the dilution and to test our esti- 

 mate of value. If we reckon 12i lbs. of ammonia and 40 tons 

 of sewage per head per annum, 1000 tons of sewage will supply 

 as much nitrogen, reckoned as ammonia, as 16^ cwt. of guano : — 



Ammonia. Guano. 



"With 60 tons of sewage, and 122 lbs., the equivalent is 11 cwt. 



"0 ,, ,, ,, 1^2 )l J, "3 >J 



40 „ „ „ 10 „ „ 13^ „ 



60 „ ,, „ 10 „ „ 8f „ 



80 ,, ,, „ 10 ,, ,, Gl ,, 



Reckoning 12^ lbs. of ammonia, the yearly sewage of an average 

 individual would represent | cwt. ; or reckoning only 10 lbs., 

 only ^ cwt. of Peruvian guano. Guano is sold at about 13^. per 

 cwt. 



The true realisable value of seicage can only be arrived at by 

 a careful investigation and comparison of the results attained 

 under favourable circumstances with judicious management. 



Crops to which Sewage is most applicable. 



Hitherto we have confined our attention to the amount of 

 nitrogen in sewage, as bearing a nearly constant ratio to the 



