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38
ing the numbers of open grids, so that the sewer gas may
be thoroughly diluted, and thereby rendered innocuous and
inert. It is clear that with well-ventilated sewers the efficient
interception of house drains (so desirable a provision) becomes
practicable by means of traps, though it is well known
that pent-up gases may force such traps or pass through
their water seals. Consequently, with badly ventilated
sewers, the sewer gas will force its way, sooner or later,
into the house drains, and so sewer gas will be laid on to
the houses. It may be stated, as an axiom, that a sewer
intercepting trap is useful according as the ventilation of the
sewer, from which it is desired (and desirable) to intercept
the drain, is efficient. The flushing of sewers and their
proper construction in the first instance are matters not to
be forgotten in this connection.
(2) Ventilation of Drains.
The remarks made in respect of sewers apply, too, to the
drains, the ventilation of which is equally as important—
an opinion now held by all sanitarians, as shown by the very
strict bye-laws recently framed by the London County Council
with regard to the ventilation of all house drains. The
object of the ventilation of house drains is to dilute and
oxidise, and thereby render innocuous and inert, drain gas—
the sewer gas being prevented from gaining access into the
house drains by the intercepting traps.
Joseph Priestley,
Mcdical Officer of Health.
January 9th, 1905.