148 
Use of Toicn Sewage as Manure. 
lime dissolved by an excess of carbonic acid. This carbonic 
acid will undoubtedly affect the insoluble parts of the fa;ces, 
especially the insoluble salts, such as phosphate of lime. In 
any plan, too, that may be adopted for precipitating the sewage 
by lime, the carbonic acid of the water must be first neutralized 
by the lime before any result can be obtained : I shall return to 
this subject presently. Then, again, the quantity of atmospheric 
air in the water causes it to act very rapidly on such fermentative 
bodies as urea in the urine, bringing about their speedy change. 
Finally, the great bulk of water thrown into the sewers is greatly 
opposed to the chance of separating and saving, by chemical 
means, the soluble matters of the sewage. Such separation could 
obviously be effected only by the production of new compounds 
more or less insoluble, and capable of subsequent removal from 
the liquid by mechanical means. But the term "insolubility " 
is, after all, only a comparative one, all compounds being more 
or less soluble. It is plain, that if the quantity of water present 
be sufficient to dissolve the new compound formed, no advantage 
will have been obtained by its formation. To take an instance ; 
the ammonia of sewage is one of its most important ingredients. 
In the daily contribution of an individual we find 125 grains of 
nitrogen equal to about 150 grains of ammonia : in whatever 
way we may seek to render this ammonia insoluble, the com- 
pound formed must be capable of resisting the solvent action of 
200 lbs. of water, or nearly 10,000 times the weight of the 
ammonia. An insolubility short of this will not suffice. 
In addition to the water supplied artificially to a town, we 
have further to consider the influence of the land and stieet 
drainage. In London, and in most sewered towns, the sewers 
serve the purpose not only of carrying off the refuse from the 
houses, but also of land and street drainage ; and it is to be 
presumed that in systems of sewerage that may be adopted for 
the future the same will be the case, unless any very consider- 
able benefits, commensurate with the increased expense, should 
be anticipated from a separate service for these wants. The 
rainfall of the district is, in many respects, a great advantage to 
the working of the sewers, as it is a natural means of flushing 
and keeping them clean, and without it the expense of flushing 
arrangements, now very great, would be considerably enhanced. 
I assume, therefore, that the sewers are charged with the duty 
of land and street drainage, and it is desired to ascertain in what 
wav, besides diluting it, these will modify the composition of 
the sewage. With regard to the land drainage we can know 
nothing — it will be what land drainage usually is, except so far 
as the foulness of the substratum of a large town may influence 
its character ; although, indeed, very little of the local rain- 
