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34
other readily practicable means, towards preventing
the generation of noxious gases in the sewers. But
under the best arrangements, it is probable that in the
summer time, offensive and dangerous gases will be developed,
which under the influence of pressure from
accumulation; of aerial currents in the sewers; and the
diffusive property of gaseous matter, will escape by
whatever external openings may exist. The question
which I have considered is how to deprive the gases of
their noxious properties as they escape. It appears to
me that the absorptive property of animal charcoal
might be usefully applied. I would propose that cages
of iron of such form of construction as experiment may
show to be the best, containing a layer of coarselydivided
animal charcoal, through which all the air
emerging should filter, befitted to the gullies. Several
practical difficulties interpose in the way of the general
application of this contrivance. If the charcoal-bed be
fitted under ground, it would be liable to get clogged-up
with mud, which would impair its efficacy as an airfilter,
and impede the flow of water into the sewer. To
fit the apparatus above ground would involve obstructions
to carriages which in many situations would be
dangerous. But these difficulties do not apply in all
cases, There are many gullies close under houses, and
in places where they might be protected from traffic,
where a cage rising six or eight inches above the groundlevel
would be of no inconvenience. The upper-grating
of the cage would be made to open for the purpose of