138 
Use of Town Sewage as Manure. 
the midst of a dense population those matters which are useless 
to the inhabitants, and which, if retained, would be destructive 
to health and life ; and as solution or suspension in water is the 
most convenient and economical method of removing them, it is 
bj tlie means of water that their removal is effected. The 
sewage of a town will, therefore, contain all that portion of the 
refuse that is practicably removable by water ; and it will be 
found that the principal matters which are not so removable 
are the manure of the stables and cow-sheds, and the ashes and 
refuse vegetable matter which it is the business of the dustman 
to cart away from the houses. For obvious reasons I do not 
include under the head of refuse those substances which are 
found of sufficient value, either agriculturally or otherwise, to 
induce their separate collection ; as, for instance, bones, offal, 
blood, and the various matters resulting fiom the trades of 
tanning, glue-boiling, »Scc. These substances are either of too 
great value to be thrown into the sewers, or, except in the cases 
of blood, are of a nature to render their removal by such means 
inadmissible. The substances which at present find their way 
into the sewage of towns are the solid and liquid excrements of 
the inhabitants, with that part of the urine of horses and cows 
which is not absorbed by their litter, the soap used in washing, 
the rain-fall of the town district, which, besides a certain portion 
of the manure of horses derived from the streets, contains, as I 
shall presently show, a considerable quantity of mineral salts 
from the same source ; and, lastly, the waste liquors of a few 
manufactories, such as the spent liquor of tanners and bone- 
boilers, and the gluten liquid of starch-makers. With regard 
to the last-named matters, however, it must not be forgotten that 
the march of agricultural improvement, which calls for an in- 
quiry like that upon which we are engaged, holds out induce- 
ment at the same time to the utmost economy of every other 
source of manure. It cannot be supposed that whilst efforts 
are being made to save the sewage of towns for agricultural use, 
and whilst the possibility of doing so is still a matter for hope, 
that the individual refuse matters produced by different manu- 
factures, and suitable for manure, will be overlooked. The result 
of an attention to these different refuse matters will be, that the 
value of sewage will have a tendency to decrease rather than 
otherwise. To take an example, blood has been for a long time 
of value, when dried, to certain manufactures, more especially that 
of the paint known as Prussian blue, but its use for that purpose 
was limited, and the demand irregular, in consequence of wliich 
much of the blood which the butchers can readily collect was 
thrown into the sewers. Lately, however, attention has been 
given to the manufacture of manure from blood, and there is 
