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155
in the sanitary administration of London and the riverian districts,
were presented to the Board in the Autumn of 1885, by its Works
and General Purposes Committee—viz., On the disposal of the
sewage of the Metropolis; and On the treatment of sewage at
main drainage outfalls. The Committee reported, November 27th,
1885, that "by chemical precipitation a good effluent water could
be obtained, and that they were pursuing their enquiries as to the
best method of dealing with the residue or sludge." As the result
of long-continued and practical experiments, conducted by Mr.
Dibdin, the chemist to the Board, to whose aid Dr. Dupre was
subsequently called, the Committee came to the conclusion that
" chemical precipitation of the solid matters held in suspension in
the sewage can be effected by the addition of various reagents, but
that no practical advantage accrues from the addition to the sewage
of more precipitating matters than are really necessary for facilitating
the natural tendency to solid deposit." It was found that the
sewage can be sufficiently clarified by the addition of 3'7 grains
of lime, and 1.0 grain of protosulphate of iron (green vitriol) to
each gallon of sewage, and by subsidence in settling tanks during
a period of from one to two hours ; the effect, being, besides the
removals of the solids, that "the grosser odours of the sewage
are destroyed, and the foul and offensive appearance removed.''
The conclusions arrived at by the Committee, and the chemist
to the Board, were submitted to four eminent chemists, Sir F. A.
Abel, Dr. Odling, Dr. Williamson, and Dr. Dupre, who reported
as the result of experiment, that while the treatment by lime
and iron " does exert a distinctly purifying effect upon the
liquid part of the sewage," the effluent, nevertheless, "retains
a sufficiently unpleasant odour to prohibit its being discharged
into the river, during warm weather, at all states of the tide but
that "the addition of manganate of soda and sulphuric acid, or
other suitable oxidising agent," to the effluent, "would so far
deodorise and purify that effluent as to allow of it being afterwards
discharged into the river throughout the year at all states
of the tide." This supplementary treatment, however, would be
unnecessary during great part of the year, when the river water