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Scientific Memoirs by

         The effluent flows from the top of the first upward tank on to the
surface of the downward filter, which is allowed to fill, and without
resting, is then discharged and carried by pipe or conduit, to—

      (3) Porous arable land at some distance, where the third stage of complete
aëration and nitrification, transforms the ammonia, nitrites and
carbonaceous residues to the final terms of carbon dioxide, water
and nitrates. The whole mechanical part of the process may be
made practically automatic, as will be shown when we discuss sug-
gestions for reform of our present methods, where also we shall deal
with the supply of water required and the method of removal.

   The above broad indications are set forth with a due sense of responsibility,
but with the confidence born of practical experience of the working of the different
types of installation now on trial in England, viz., the Septic tank, the Scott-
Moncrieff plan and the systems of downward filtration, intermittent and continuous
(the Dibdin, the Ducat, the "Absaf" processes). These last are entirely unsuited
to the concentrated sewage of cantonments, and of natives, even with the most
extravagant preliminary dilution with water. If the outward forms of the apparatus
be legion, there are, in truth, but two types; the one which makes a preliminary
hydrolytic process essential previous to oxidation, and the other, which relies on
fermentation in the presence of air throughout, and where the different stages
we have followed are perforce confused. The marked differences in the character
and strength of the sewage in India and in England respectively, sufficiently
indicate that the latter processes, which may deal creditably with the excreta
diluted with 30 to 40 gallons per head, after a long passage through sewers,
(where the hydrolytic transformations are largely carried on) are entirely out of
place in India, where the dilution is much smaller and where the unabsorbed
proteid from vegetable food amounts in the excrement to as much as 10 to 20
per cent. of the total ingested, and where also from 30 to 50 per cent. of the
Cellulose leaves the body in its integrity, and can only be decomposed under
anaërobic conditions.

Necessity for pre-
liminary anaërobic
stage.

   And it may be added that an enormous economy of space and apparatus
accrues from the division of labour obtained by a preliminary anaërobic hydrolysis,
where concentrated sewage has to be dealt with, and as Scott-Moncrieff has said,
the stronger the sewage the more vigorous and complete is the fermentation set
up in the anaërobic stage. Finally, it is absolutely certain that it is radically
unscientific to depend solely on downward filtration, where all classes of organisms
are confused in antagonistic action; and in practice, as the writer has proved,