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67
The experiments on anaerobic digestion of sludge initiated at Crossness have
been continued and a larger plant is to be constructed at Barking.
In the report for 1933, the summer of that year was described as phenomenally
River
Thames.
dry and not followed by winter rains. The cumulative effect of two dry summers
was shown in the river early in 1934, when the naturally low flow of the river was
further reduced by the demands of the Metropolitan Water Board. Chemical
examination showed that the transitional state of sewage treatment in Middlesex
affected the upper tidal reaches under these unusual conditions, and throughout
the summer and well into the winter the river was in an unsatisfactory condition
throughout the tideway as well as in regions where the summer condition is unfavourably
affected by the effluent from the Council's outfalls. It is worthy of record that
proportions of sea water approaching 7 per cent, were found at high water as high
up the river as Kew. When the large new works being erected by the county councils
of London and Middlesex are in operation a great improvement throughout the
tidewav mav be expected.
During the summer ot 1934 the number ot swimmers in out door baths and
lakes controlled by the parks department was very great. At some of the baths
fitted with plants for filtration and chlorination, it was only by continuous purification
that the water was kept in satisfactory condition, but in one very large bath it was
found necessary also to chlorinate the water in the bath at night in order to bring
it to a satisfactory condition after a period when the number of bathers had been
excessive. In very large baths it appears that, apart from the difficulty of avoiding
streaming from inlet to outlet and consequent patches of water which are only
slowly changed, the time of travel of water along the bath may, when the number of
bathers is great, be sufficient for all the free chlorine to be expended unless the
initial concentration is of an order which might cause irritation of the eyes and other
delicate surfaces of the body. It is believed that this difficulty can be overcome by
the use of ammonia in addition to chlorine. This chloramine treatment is being
adopted at the large bath referred to above.
Swimming
baths and
lakes.
Three lakes, one relatively large, were used to so great an extent that, although
the water was chlorinated in as efficient a manner as was possible, it was found necessary
to close them to bathers on account of the unsatisfactory state of the water both
as regards bacterial content and turbidity.
One was, later in the year, allowed to be used to a limited extent by early morning
bathers. These lakes will in the near future be replaced for bathing purposes by
baths equipped with filtration and chlorination plants.
The experience of the past summer has strengthened the conviction that shallow
stagnant baths or lakes cannot be kept in satisfactory condition in summers when the
weather induces large numbers to use them. Even with a limited use by clean
bathers it is very difficult to keep artificial pools, where a proper balance of aquatic
flora and fauna cannot be maintained, in a proper condition.
The systematic investigations commenced in 1928 as to the condition of the air
in Blackwall and Rotherhithe tunnels were continued during 1934, and in addition
to examinations made during the rush period on Monday mornings, the carbon
monoxide content of the tunnel air was determined on several occasions in 1933
and 1934 during the evening rush period and on other mornings than Monday.
Vehicular
tunnels.
The visibility in all directions from the fleche of County Hall was above the
average of previous years in all months of 1934 with the exception of November.
In this month a week of exceptional fog depressed the average, and, besides, both
maximum and minimum on any one day were low. The maximum for December
was as high as that for March. Observations east of the Nore were not available
for the winter months. The accompanying graphs (figs. 2 and 3) present the summarised
results of all observations. In order to make them more generally useful,
the international telegraphic code numbers and the meteorological office indication
letters are shown on the scale of ordinates on both graphs as well as the distance in
miles.
Visibility.
Also for each month the distance and direction of the furthest visible object
or objects are shown as well as the average in all directions for all week-days. It