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For the purpose of clarification, or precipitation of the solid
matters, lime and green vitriol were employed, supplemented by
the addition of manganate of soda and sulphuric acid to the
effluent when necessary. These last-named materials, however,
were alleged to be unnecessary when the river water and the
sewage were cool, and the latter much diluted by rainfall. But
their addition, it was stated, purified and deodorized the effluent
to such an extent as to render its discharge into the river
unobjectionable at all states of the tide, a statement very
generally traversed. I mentioned also that the Board, in order
to prevent nuisance within the Metropolis arising from the discharge
of offensive gases from the sewer ventilators, were
applying the manganate and acid, at numerous stations, to the
sewage as it flows through the main sewers. It was hoped that
this plan would ensure the arrival of the sewage at the outfalls
in a deodorized condition, and thus assist in the production of a
satisfactory effluent. The object the Board had was to avoid the
necessity for costly land filtration of the effluent, recommended
by the Royal Commission on Metropolitan Sewage Discharge,
with a view to ensure the removal of all odour and the possibility
of ''secondary fermentation." The Board, in giving effect to
the views of their scientific advisers, incurred a large expenditure
for works of construction, and in the carrying out of the
system adopted.
SIR HENRY ROSCOE'S REPORTS.
Deferring, however, to the objections made to the system
above described, the Board, in 1887, retained the services of Sir
Henry Roscoe, as consulting chemist, and scientific adviser
in this matter, and they ultimately consented to the request by
Sanitary Authorities—your Vestry among the number—to make
that gentleman's reports public. These reports were five in
number. The first, dated 16th May, 1887, dealt with "The
Deodorization of Sewage in the Metropolitan Sewers," the
second and third, dated August 7th and December 9th, 1887,