14G Use of Town Sewage as Manure. 
on the dry weight, we observe in two out of three cases a most 
material reduction in the percentage of nitrogen by the solvent 
action of water. In the sample B the alteration is very small, 
but in A it amounts to 20 per cent., and in C to 30 per cent, 
of the whole contents in nitrogen. It is obvious, therefore, that 
where, as in the case of sewage, the solid faeces are subject to the 
washing action of water, their ordinary composition must be 
altered by the abstraction of all matters tliat are soluble in water. 
It is hardly necessary to prove that this will be the case with 
soluble alkaline salts to fully as great an extent as in the case of 
nitrogen, and we may assume tliat when the solid excrements 
are thoroughly mixed up and incorporated with abundance of 
water, all that they contain of value in the soluble condition is 
transferred to the liquid through which they are distributed. 
Furthermore, in the course of a long transit to the outfall of a 
sewer — more especially if from structure of that sewer the 
escape of the matters is delayed — changes in the solid excre- 
ment of a fermentative kind cannot fail to go on, which are con- 
tinually transforming the nitrogenous portions of the solid 
matter into a fluid state. I shall have occasion to revert to this 
again, and will not therefore dwell upon the subject farther than 
to observe, that in judging of the probable value of solid sewage 
refuse, as collected by the simple means of subsidence or filtra- 
tion without chemical agencies, we should deceive ourselves if 
we were to compare such matter for an instant to the ordinary 
solid human faeces — much more if we took for the standard of 
its value night-soil which from open privies is the mixed solid 
and liquid excrement unwashed and undiluted by water. 
Such being the nature and relative proportion of the solid and 
liquid excrements of a population, let us for an instant consider 
what quantity of water is employed in their removal by the 
sewers. 
By the official returns of the different water-companies made 
to the General Board of Health, it appears that the gross daily 
quantity of water supplied to the metropolis amounts to 
44,000,000 gallons.* The greater part of this, or about 90 per 
* As illustrating the magnitude of the question of metropolitan sewerage, it 
may not be out of place here to quote a few passages from the Eeport of the 
General Board of Health on the Water-supply of the Metropolis : — 
" The gross daily quantity of water pumped into the metropolis amounts, ac- 
cording to the preceding returns, to upwards of 44,000,000 gallons. In order to 
give a conception of the quantity of water thus delivered, it may be stated that the 
daily supply would exhaust a lake equal in extent to the area of St. James's Park, 
30 inches in depth; that tlie annual supply exceeds the total rainfall of 27 inches 
over the populated portion of the metropolis (25 square miles) by upwards of 50 
per cent. ; and that it would cover an extent of area equal to that of the city (or 
about one square mile) with upwards of 90 feet depth of water. 
" The daily supply would, however, be delivered in tweuty-four hours by a 
