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certain types of paints and surfaces and advice was given in a number of cases as to
the best types of material to use and procedure to adopt.
Other building materials examined included cements of all kinds, bricks of many
varieties, asphalts, synthetic stones, concretes, timber, synthetic floorings, clinker,
mortar, putty, slates, bitumen sheeting, etc. The considerable number of synthetic
floorings submitted for analysis as to composition and for test as to efficiency under
various conditions indicated particular interest in this line. Many materials tendered
as hardeners or waterproofers for concrete were examined and their probable efficiency
assessed: examples were calcium chloride, mixed soap solutions, hydrated lime with
chalk and soap, alkali silicates and soap, and emulsion of a urea-formaldehyde resin,
etc. The possible danger of sulphates to concrete was carefully watched and many
samples of soils and waters from housing sites were analysed, the use of sulphate
resisting cement or high alumina cement being recommended where the sulphate
content indicated the need for such precautions. Some suspected cases of dry rot
were examined for the presence of the active agent Merulius Lacrymans. Other
special items were :—(a) a surface hardener and skid proofer for concrete was alundum
i.e..electric furnace produced aluminium oxide containing a small amount of aluminium
carbide ; (6) a neutralising fluid for treating new plaster was an aqueous solution of
zinc fluorosilicate ; (c) a glaze producing process for wood was based on the polymerisation
of urea-formaldehvde in the presence of an organic phosphate and an organic acid.
Rivers and
drainage
The formation, early in the year, of a separate Rivers and Drainage Committee
of the Council emphasised the importance attached to the subject of river
sanitation and the associated one of sewage treatment.
The sewage from London north of the river Thames is treated at the Northern
Outfall Works, Beckton, by sedimentation, and about one-third of the flow, subsequently,
by the activated sludge process. That from London south of the Thames is
subjected at the Southern Outfall Works, Crossness, to sedimentation only. In both
cases most of the sedimented matter (sludge) is taken out into the estuary in ships
and dumped ; the effluent is discharged into the river at the outfalls. The sludge
digestion plant at the Northern Outfall Works dealt with a small proportion of the
sludge, and the sludge gas produced (containing about 70 per cent, methane) was used
for power production on the works. The composting of sewage products with pulverised
household refuse was continued, considerable quantities being made during the
year from sludge screenings and subsequently transported mainly to farms at hospitals.
The final effluents from the Outfall Works are discharged into the river Thames
and biochemical oxidation by the dissolved oxygen in the water is the final process in
their purification. The condition of the water of the river is, therefore, of great
importance and a careful watch was kept upon it by regular weekly sampling and
analysis at many points between Teddington Weir and the sludge dumping area in
the estuary. In order to improve its condition the Council approved, in principle,
large additions to the present treatment works on both sides of the river and the
construction of new sedimentation tanks at the Northern Outfall Works was started
during the year.
Two other important factors which affect the condition of the water are the
freshwater flow and the water temperature. The statutory minimum for the former
is 170 million gallons per day which can, by Order made by the Minister of Health,*
be reduced, under certain circumstances, to 50 million gallons per day. A large
proportion of London's water supply is drawn from the upper Thames by the Metropolitan
Water Board and a scheme was agreed by the authorities concerned for the
withdrawals to be regulated to the best mutual advantage. In regard to the temperature,
a Government Committee was set up by the Minister of Health to examine the
effect on the river of the admission of heated effluents and the Chemist-in-Chief was
* Now Minister of Local Government and Planning.