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conclusively proving that in the case of an ordinary domestic
sewage, septic tank liquor was not more easily oxidized on its
passage through filters than other liquids.
These experiments have borne out most conclusively that I
was right in recommending the adoption of the Dibdin Slate Bed
System. These beds had not been in work long enough for the
Commission to take cognizance of their result. They mention the
fact that "Mr. Dibdin has lately advocated the use of a large slab
of slate in primary contact beds"; they say further that as a result
of our inspection of the beds at Devizes, we came to the tentative
conclusion that primary beds containing these slate slabs must be
regarded more as preliminary settling tanks than as a contact bed;
but we have proved much more than this in the two large slate
tanks we have had working for the last two years—first, that they
are aerobic and digestive, and their action is exactly the reverse of
the septic tank, which is anaerobic producing much sludge, sulphurated
hydrogen, sulphides, and smell, its effluent liquor clogs the
succeeding filter beds, and when delivered into a stream the
chemical contents are broken up and redeposited, forming black
stinking mud.
From two years' experience of our slate beds, I have been
struck by the fact that nearly all our visitors go away with the
erroneous idea that the "black humus" that adheres to the slates
and bottom of the slate tanks is ordinary sludge, but this is not so;
this is a deposit on the slates from the aerobic action of the
organisms found in the sewerage: really "living earth," the portion
I have now before me which I retained and which was scraped off
the slates on October 8th, 1908, and have had in an ordinaryenvelope
in my consulting room during the whole time, was at first
soft but inodorous, containing living worms and organisms, but
has never emitted any smell, becoming dry, clean, not soiling the
fingers when handled and inodorous.
In properly constructed slate tanks it has been proved that
no sludge remains; you may have, after some years, an accumulation
of a black jelly-like inodorous deposit, which is known as
humus, is easily pulverised by exposure to air, but in no case can
you accumulate the large quantity of stinking sludge produced by
chemical and septic tank treatment.
It has proved at Devizes and New Maiden most satisfactory
and economical, carrying out the maxims laid down by the Royal
Commission in their report. I have little doubt that the next Royal
Commission, after careful examination, will recommend this system
as efficacious and economical.
We are at present laying down extra filter beds; when
finished, the system will, I hope, be completed as a whole with Dibdin's
slate bed method. In the Journal of the Royal Medical Corps,