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36
(air) tests are the only reliable tests, but too severe for the routine
testing of drains of old buildings. The pneumatic (air) test is
comparatively new, and most delicate, but is not much used in
London.
Bearing this explanation in mind, the statistics are still useful
as showing that year by year the number of defects found decreases.
Taking the statistics for the Parish of Lambeth during
10 years (1891-1900), it will be noticed that the percentage of
houses showing defective drains has decreased from 22.3 in 1891
to 14.3 in 1900, whilst the percentage of houses showing defective
traps, fittings, and appliances has decreased from 41.4 to 30.2
per cent. during the same 10 years. Table L gives full particulars,
with the averages for the 10 years worked out, and on comparing
these (which relate to the old Parish of Lambeth) with
those for 1902 (relating to the new Borough of Lambeth) it will
be seen that the latter show a decrease of 33.4 per cent. below
the average in respect of defective drains.