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lower and more polluted reaches. These years would appear to have been particularly favourable to
the success of the reduced treatment which war conditions necessitated.
At the present stage it is possible to arrive at tentative conclusions only, but the chemical
results so far obtained show that the continued inoffensive condition of the river, about
which there can be no question, has not been due to the absence of sources of pollution or to
the fact that the dilution has been so great as to lead to a clean and well oxygenated stream. The
evidence of unoxidised polluting matter in the water is at times apparent, more particularly in the
neighbourhood of the outfalls and the proportion of dissolved oxygen has frequently been low over
considerable stretches of river. The state of equilibrium, which the co-existence of such conditions with
inoffensiveness indicates, appears to be due to the fact that those natural processes of purification which
go on continually in any body of polluted water, do so at a particularly high rate in the Thames where,
owing to the tidal movement, the mixing and agitation of water and of mud deposited at slack water
is very rapid. This acceleration of processes of oxidation leads to a reduction in the proportion of oxygen
in solution, which might be held to indicate a serious state of affairs in stagnant water or in a slowmoving
or non-tidal river. It is evident from the facts, and is capable of explanation on theoretical
grounds, that such results in a swift tidal stream demonstrate that purification is going on at a very
rapid rate. The continued oxidation of matters in suspension or of mud which is not allowed to
accumulate permanently, no doubt largely accounts for the small proportion of dissolved oxygen
frequently found in the Thames water. This is a much more satisfactory condition than has been found
in more slowly moving waters, where relatively high aeration was found to be accompanied by the
presence of a fermenting river bottom.
It was suggested to the Council towards the end of 1916 that pollution of portions of the Thames
estuary which had been observed at times, might be due to the travel of sewage matter from the altered
area of discharge. The area which it was suggested might be affected was therefore examined under
the supervision of the Chemist, by two officers in his branch of the department, Messrs. J. W. H. Biggs
and E. R. Andrews, in January and February, 1917, under very adverse weather conditions, which were,
however, of the kind which had been considered most likely to lead to pollution from the discharging
area used by the Council and other bodies. The investigation included a bacteriological and some
chemical examination of samples of water taken under varying conditions of tide and of mud collected
at certain selected places in the area. As the outcome of this investigation, it was found that the results
were not compatible with the hypothesis that contaminated material is brought inshore by the combined
action of the wind and tide in the manner suggested, and this, notwithstanding the fact that during the
investigation the prevailing winds and conditions generally were theoretically favourable to such a
movement.
43516 C