Use of Totvn Sewage as Manure. 
147 
cont., is supplied to private houses ; all other supplies, inclutl- 
ine: larji;e consumers (in manufactories), flushing of the sewers, 
road-watering, and fires, making up the other ten per cent. But 
in whatever manner tliis water is distributed, it ultimately finds 
its way into the sewers. The population of London is rather 
more than 2} millions, and the daily water supply is therefore 
in round numbers 20 gallons per head. There are those indeed 
who believe that this quantity is unnecessarily great, and that 
modifications in the system of sewerage, and aljove all the intro- 
duction of tubular instead of brick draining, would tend materi- 
ally to diminish the quantity of water necessary for town supply. 
Taking, however, into account the quantity of water thrown 
into the sewers by the rainfall, and which amounts to nearly half 
as much as that supplied artificially, we are safe in assuming the 
smallest quantity of water which is at any future time likely to 
pass through the sewers of a town, at 20 gallons per head of the 
population. It may be much more, but it cannot well be less. 
Twenty gallons of water weigh of course 200 lbs. ; so that the 
solid and liquid excrements of each person, containing altogether 
only about 1000 grains of solid matter, more than half of which 
is soluble, are distributed through 200 lbs. (1,400,000 grains) 
of water. In other words, the solid matter of the urine and faeces 
is mixed with 1400 times its weight of water. 
Here is the great difficulty of the subject, and one which so 
many people seem to forget. We have not to deal with ordinary 
excrementitious matter, but with that matter diffused through an 
enormous bulk of water ; to pick over the bundle of hay to find 
the needle. If it be desired to separate by filtration the in- 
soluble matter of the sewage, we have to filter nearly 3000 tons 
(more than half a million gallons) to obtain from it one ton of 
dry manuring matter. 
This vast quantity of water, in relation to the excrementitious 
substances of the sewage, has more influence in many respects 
upon the question of its employment than would at first sight 
be supposed. In the first place, whatever be the composition of 
the water supplied, the effects of that composition must be felt 
by the faecal matter. A great deal of water, perhaps the largest 
portion of the water supplied to towns, contains carbonate of 
brook 9 feet wide and 3 feet deep, running at the rate of 3 feet per second, or a 
little more than 2 miles per hour ; and three sewers of 3 feet in diameter, and 
of a proper fall, will suffice for the removal of the same volume of refuse or soil- 
water. The total weight of this annual supply of water is nearly 72,000,000 tons. 
The daily cost of raising the wljole quantity by engine-power 100 feet high 
would be about 25Z., or about 9000Z. per annum. The average daily quantity 
pumped into the districts, exclusive of the supplies to large consumers, and of the 
quantity used for all public purposes, would, supposing it were equally distributed 
for each house, occupy about fifty pailsful, and would weigh about 1 3 cwt." 
L 2 
