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chlorinated rubber paint and bituminous paint, the classification depending primarily on
the results of the analyses and tests made by the Chemical Branch. Samples of deliveries
were also taken at the sites in order to ensure that the quality complied with the standard
required. The technique of paint testing has advanced considerably in recent times and,
in order to ensure the efficiency of the examination, the Council agreed during the year
to expenditure necessary for equipping a new paint-testing laboratory at County Hall
with the latest apparatus. In addition to facilities for determining the film hardness,
flexibility, etc., provision is being made for an accelerated weathering test apparatus. A
feature of the year's examination of products for approval was the large number of
emulsion paints submitted. The majority of these were based on water emulsions of
polyvinyl-acetate and it was necessary to study the properties of such materials and work
out a suitable scheme of examination.
Examples of a few defects were (a) the use of lithopone in a paint for exterior work;
(b) offensive and toxic nature of the medium; (c) insufficient mixing before use. Special
matters dealt with referred to: (a) colour permanence of applied paint (i.e., the fastness
to light), (b) primers for hard-boards, (c) fire resistant paints, (d) paints for specially
corrosive conditions, e.g. sewage.
Much advice was sought regarding building materials and allied problems. A few
examples were in relation to cements, asphalts, bitumen sheeting for roofing, etc.,
synthetic floorings, sand, plasters, mortars, etc. For example, many types of flooring
materials were examined to ascertain their chemical composition, water absorption, shock
and fire resistance, thermal conductivity, durability and liability to staining by certain
materials. Their composition varied widely: coloured Portland cement, magnesium
oxychloride, bitumen and sawdust, high alumina cement and rubber latex, powdered
wood and resin were typical examples. Such a variety introduces not only problems in
regard to construction but also as to cleaning and polishing. Plaster defects were investigated
in some cases and the causes diagnosed. Asphalts were generally satisfactory
as regards the bitumen content but in some cases adverse comment was made as to the
grading of the aggregate. Materials for the eradication of wood-boring insects were
examined and recommendations made. On the planning side the advice of the Chemical
Branch was sought in many cases in regard to the Use Classes Order, 1950, relating to
the Town and Country Planning Act, 1947; guidance was sought as to the exact
classification of proposed industries with respect to the possible causation of nuisance or
effect on the amenities of the areas in which their sites were located.
Public health
The examination of water supplies is an important part of the work of the branch
from this aspect, for, although in the majority of cases the water is derived from the
mains supply, there are a number of schools and other premises at which it is drawn
from private wells. In these cases, before use, it is chlorinated by means of automatic
dosing appliances. The Chemical Branch carries out regular monthly inspections (in
addition to the daily free chlorine tests made by the resident engineer) and samples are
taken for chemical analysis and bacteriological examination in the laboratory. Some
hospitals formerly under the control of the London County Council which have private
well supplies have, at the request of the hospital committees, continued to be included
in the regular examination programme.
The air in the Council's vehicular tunnels under the River Thames was regularly
tested in order to ensure that the carbon monoxide content did not exceed the safety
limit. In view of the continued use of petrol containing lead compounds, the lead content
of the air was also checked periodically and found to be safe. Since nitrous fumes can
be caused by diesel engines this constituent also received attention but it was well within
safety limits.
Considerable work was done during the year on atmospheric pollution, assays being
made by various methods of the polluting matter (total deposit, tarry matter, sulphur
gases, smoke, etc.) in the air at various places within the County and also, for comparison,
at two observation stations outside it. This work was done in conjunction with a scheme
sponsored by the Department of Scientific and Industrial Research.