Sewafje- Farming. 
395 
alumina is the agent employed for the clarification and utilization 
of sewage. It would be premature, at present, to pronounce any 
decided opinion upon this scheme, but there seems no doubt that a 
valuable manure can be manufactured by it, since Dr. Voelcker 
has estimated the worth of various samples of such manure at 
from 21. 15a'. to 11. Is. per ton. As, however, we are not told what 
proportion of phosphate was added in eacli instance, and at 
what cost, we have no means of judging how much of such sums 
was due to the sewage itself, and how much to the added 
phosphate, but the value of the deposit depends entirely upon 
the quality of the sewage and the quantity of phosphate added. 
The clarified sewage, it is announced, loses none of its mineral 
fertilizing matters, and becomes slightly richer in saline ammonia. 
As, therefore, most of the ammonia it appears escapes with the 
water, the invention would hardly seem to be one of much 
practical utility, because the trouble and expense of treating the 
deposit would, probably as in other cases of the kind, annul 
the benefit derived from the use of clarified sewage. I do not 
learn from the prospectus of the Company that it professes to be 
able to do more than make clear the effluent sewage, and at 
present the extraction of the ammonia seems the one thing 
needful to render any process of this kind hopeful and satis- 
factory. 
I now come to the water-closet and sewage-irrigation system, 
the only one of the three which (as has been seen) is at present 
applicable to towns with any prospect of success ; which com- 
bines perfect cleanliness with considerable economy, and which 
meets in any degree the needs of agriculture. When we remember 
the necessity of water-supply — the fact that it forms a cheap and 
expeditious carrier, and that the earth is one gigantic filter, ever 
ready not only to absorb but to utilise the impurities of sewage — 
we can no longer wonder at the growing popularity of a system, 
the manifest advantages of which may lead to its adoption in all 
large collections of human beings. 
" Sewage traversing the soil undergoes a process to some extent 
analogous to that experienced by blood passing through the lungs 
in the act of breathing. A field of porous soil, irrigated inter- 
mittently, virtually performs an act of respiration, copying on an 
enormous scale the lung-action of a breathing animal ; for it is 
alternately receiving and expiring air, and thus dealing as an 
oxydizing agent with the filthy fluid which is trickling through 
it. And a whole acre of soil, 3 or 4 feet deep, presenting within 
it such an enormous lung surface, must be far superior as an 
oxydizer for dealing with the drainage of 100 people to any filter 
that could be practically worked for this purpose. . . . Moreover 
the appetite of the soil is constantly kept alive and fresh (except 
2 D 2 
