Utilisation of Toion Sewage. 
79 
above shows, however, as was to be expected, that the average 
composition of the sewage collected in the two fields was almost 
identical. The only difference of any importance is in the 
amount of suspended matter ; there being less organic matter, 
inorganic matter, and ammonia, in suspension, in the sewage 
collected in the 10-acre field than in that from the other. 
" Without going into any detail on the point on the present 
occasion, attention may be called to the fact that the column 
showing the amount of the several constituents in 1000 tons of 
the sewage, considered, in relation to the amounts of increased 
produce obtained by that quantity of sewage, as shown in Table III., 
indicates that the constituents of dilute liquid sewage can by no 
means be valued at the same rates as those in portable, artificial 
manures, such as guano. In illustration it may be stated that 
the quantity of ammonia estimated to be contained, on the 
average, in 1000 tons of the sewage, is equal to the nitrogen of 
the mixed excrements of about 21 or 22 persons of a mixed 
population of both sexes and all ages for a year, and to that in 
about 11 cwts. of Peruvian guano ; and the total solid matter in 
1000 tons of the sewage is seen to be somewhat more than a ton. 
The average amount of increase of produce obtained by the 
application of this large quantity of manurial matter was, how- 
ever, only equal to about three-fourths of a ton of hay ; never- 
theless, as has been shown, the increase of grass bore a pretty 
obvious relation to the amount of sewage employed, until the 
latter approached (during the actual period of the experiment) 
the rate of about 9000 tons per acre per annum. 
" It is further worthy of remark that the mean composition of 
the Rugby sewage, as given above, differs comparatively little 
from that which published analyses indicate for the sewage of 
London ; and the correspondence is the closer when, having 
regard to the relative amounts of sewage to which the different 
analyses are applicable, the calculated average instead of the 
mere arithmetical mean composition of the sewage is taken in 
the two cases. Thus, the average proportion of total solid matter 
in the Rugby sewage for seven months, up to the end of October, 
1861, was about 77^ grains per gallon, whilst the average 
amount in London sewage appears to be about 91 grains. The 
correspondence in the amount of ammonia, which, more than 
any other constituent, indicates the relation of population to the 
amount of water, is, however, much more striking. Over the 
seven months the average amount of ammonia in the Rugby 
sewage is estimated to be 6"65 grains per gallon ; and, founded 
on^ the rate of flow of sewage and the analyses given by Dr. 
Letheby of both the day and night sewage from 10 different 
sewers, the average amount of ammonia in the sewage of London 
