Use of Toion Sewage as Manure. 
151 
fectly well tliat tliere are various kinds of matter thrown into tlio 
sewers which, in a rigid theoretical examination of tlie composi- 
tion of sewage, should be taken into account, but I am convinced 
tliat the one which I have adopted is the practical common-sense 
view of the question The supplementary ingredients are, in 
relation to the fa?cal matters, quite insignificant in quantity,^ 
and, as I before observed, they w'ill necessarily be on the de- 
crease, since it is absurd to suppose, in the presence of a 
growing demand for artificial manures (for which at present the 
supply is quite inadequate), that concentrated liquids (as cows' 
urine for instance) will be permanently allowed to escape into 
the sewers and get diluted, to an enormous extent, only to 
undergo in the sequel expensive chemical processes for their 
separation. 
If any arrangements should finally be carried out for the 
use of the tohole sewage in agriculture, then no doubt there will 
be less object in keeping out of the sewers the substances in 
question ; but if the sewage is to be subjected to operations to 
separate the fertilizing matters from the water with which they 
are mixed, the sewers will ultimately receive only those matters 
which either cannot be profitably employed in the direct manu- 
facture of manure, or which a due regard to public health and 
decency will not permit to be so employed. 
We have dwelt thus long on what is likeh/ to be the compo- 
sition of sewage in accordance with our knowledge of the mate- 
rials which enter into it, because it is next to impossible to 
determine that composition by direct examination. The nature 
of the sewage not only varies with the population of the district 
from which it is derived, but is different at every hour in the 
day. To ascertain with any amount of precision the actual 
composition of sewer water, we must take samples from many 
different sewers, and on repeated occasions. A satisfactory 
result could only be obtained by an amount of labour and ex- 
pense which it would hardly repay, and which no private indi- 
vidual is likely to incur. There is only one other way by which 
an approximation to the truth might be obtained, and that is by 
a careful inquiry into the food of the population.* With the 
caution that they only apply to particular samples and condi- 
tions, I will shortly give the results of some examinations of 
sewer-water which I have made.f 
* I believe that Mr. Lawes has been at some pains to obtain the data for such 
an estimate in the case of London ; and it is to be hoped that he will be induced, 
at some early period, to give his results to the public. 
t Examinations of the sewer-water of London have been made by Drs. Miller 
and Playfair, by Professor Brande, and several other distinguished chemists. As, 
however, my own analyses have been made with an exclusively agricultural object, 
I may be pardoned for preferring them on this occasion. 
