Toion Sewage. 471 



About three-fourtlis of the theoretic money value of the con- 

 stituents of sewage is due to the ammonia (or nitrogen reckoned 

 as ammonia) which it contains. The relation of this ammonia 

 to the other valuable constituents is nearly constant, consequently 

 the same result is obtained by ascertaining and valuing the 

 ammonia, and then increasing the value so fixed by one-third 

 as by elaborate calculations, including all the constituents. It 

 appears that ^d. per lb. of ammonia, or one farthing per ton of 

 sewage for every grain of ammonia per gallon, would fairly 

 represent the total value of the manure as tlius determined. 



After much hallucination, authorities have come pretty nearly 

 to an understanding as to the average composition of London 

 sewage. 



In the summer of 1863, Baron Liebig, adopting as the basis 

 of his calculations an analysis of the Dorset Square sewage by 

 Mr. Way, which showed nearly 18 grains of ammonia per 

 gallon, estimated that (with such an addition of phosphate as 

 he considered requisite to render the whole of the ammonia 

 available) the constituents in 1 ton of sewage of that composition 

 would be worth about Aid. Now, according to the estimate 

 stated above, 18 grains of ammonia per gallon would indicate a 

 value of 18 farthings, or A.^d. for the total constituents in 1 ton 

 of the sewage. 



In January, 1865, Baron Liebig assumed the average sewage 

 of the metropolis to contain only 7'2 (instead of IS) grains of 

 ammonia per gallon ! and he estimated the value of the consti- 

 tuents in 1 ton of such sewage to be rather over Ifrf. Our 

 estimate would also give rather over 7 farthings, or Ifc?. 



In 1857, Messrs. Hofman and Witt concluded from their 

 investigations that the average dry-ioeather sewage of the metro- 

 polis contained about 8*2 grains of ammonia per gallon ; and 

 taking into account the ammonia, organic matter, phosphoric acid, 

 and potassa, valued one ton at about 2'lld., a sum almost iden- 

 tical with that resulting from our theoretic estimate. 



The estimate of INIessrs. Hofmann and Witt, be it remarked, 

 applied to the normal dry-weather sewage (about 158,000,000 

 tons per annum), yet it was adopted by Mr. Ellis in his appli- 

 cation for the concession of the metropolitan sewage, as applying 

 to the whole amount of dilute sewage (inclusive of rainfall and 

 subsoil-water) 266,000,000 tons, and his calculations of profit to 

 his company, and to the rate-payers were based on this erroneous 

 assumption. 



Baron Liebig likewise based his estimates on the total sewage 

 supply. 



The following Table indicates the remarkable fluctuations, 

 according to circumstances, in the composition of London sewage, 

 and the consequent danger of hasty generalisation. 



2 I 2 



