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the sewers at all, it may prove possible to do so as effectually and
more cheaply by the use of other chemicals than manganate of
soda and sulphuric acid. Bleaching powder and sulphurous
acid, he says, would be cheaper, and probably as efficacious, and
he recommended experiments with these two disinfectants, in
place of, or in addition to the manganate, for the purpose of
comparison. Meanwhile Sir H. Roscoe does not consider the
expenditure (£40,000) for the purpose of the manganate
deodorization justifiable. The method proposed in a subsequent
communication (June 10th, 1887) is that adopted in 1870-73,
of dropping solutions of the disinfectants on to a cloth suspended
in the ventilating shaft—a method which was proposed and
carried out in this parish by the Surveyor to your Vestry, at, I
believe, a still earlier date, a tow curtain being used in place of
cloth. Sir H. Roscoe states that the object thus to be arrived
at is simply to deodorize the sewer emanations (and not to disinfect
the sewage itself): the most " effective method of accomplishing
this, however, is, wherever practicable, to dilute the
sewer emanations with fresh air, by means of suitable ventilation."
(2.) The Report on Deodorization of Sewage at the Outfalls
(August 7th, 1887) records the results of a month's trial of
chloride of lime (bleaching powder) as a deodorant, the effluent
being successfully treated by addition of five grains to the
gallon.
(3.) Following up the Report of August 7th, Sir Henry Roscoe,
on December 9th, 1887, addressed a more elaborate Report to
the Board, dealing with Deodorization of the Sewage at the
Outfalls, July—October, 1887. Reference is made in the Report
to the experiments with bleaching powder, followed up as these
were by experiments with manganate of soda and sulphuric
acid. Before entering into details of the question of the relative
value of the two deodorants employed, Sir H. Roscoe expresses
his strong conviction that " the use of chemicals of any kind