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vening period in the increase of scientific knowledge. This, of course, has had its
repercussions in the development of new manufacturing processes involving chemical
synthesis. Examples which may be quoted are in regard to modern and more effective
insecticides (e.g. D.D.T. and Gammexane) and synthetic resins and dyestuffs for use in
paints, etc. Thus, at the beginning of the period, paints generally consisted of a simple
inorganic or natural pigment compounded with linseed oil and turpentine: the pigment
could, for instance, be manufactured white lead or natural ochrc; the chemical preparation
and subsequent analysis of such a material was a comparatively simple process.
Nowadays the pigment may contain a fast artificial dyestuff (such as monastral blue)
mixed with other substances, and the medium, instead of being just linseed oil, may
contain synthetic resins or chlorinated rubber. Such a complex mixture is extremely
difficult to separate chemically and hence other methods of assessing the suitability of
the paint had to be developed. These have been mainly on the lines of physical testing :
for example, the film produced by the paint on painting out is examined for such
properties as elasticity, flexibility, gloss and gloss retention as well as being exposed to a
process of accelerated weathering. The requirements of modern architects for a much
extended series of colour ranges and the need for a scientific assessment of these in the
case of samples examined has also complicated the position.
Incidentally, these considerations illustrate the fact that the Chemical Branch deals
not only with the chemical aspects of the requirements of the service, but also with
those of the Wlated sciences, particularly physics.
Another field of activity of the Chemical Branch in which the scientific aspects and
analytical control have become of much greater importance than in the old days is that
of sewage treatment. Formerly the system of operation was to add a small dose of
chemicals, settle in sedimentation channels, decant the liquid direct to the river, and
pump the settled sludge to a sludge vessel for dumping in the North Sea. But in 1913
the 'Activated Sludge' process was invented by two chemists at Manchester, and, later,
the 'Sludge Digestion' process was devised by a chemist at Birmingham. These two
procedures revolutionised the science of sewage treatment ; they arc both biological in
character and need careful analytical control to ensure that the conditions are suitable
for optimum operation. Whilst both were great developments the latter is possibly of
more obvious value since it yields sufficient sludge gas (containing 70 per cent. methane)
which, on combustion, will produce enough power to render the sewage works selfsupporting
from the power point of view. Both these processes have operated at the
Northern Outfall Works for some years and will do so on a much larger scale at both
works when the additional plants, now under construction or authorised, have been
completed.
One aspect of the work of the Chemical Branch which should be emphasised at the
present time is its economic value. In many instances savings of expenditure have been
achieved by means of its activites. For example, by the scheme of approved lists for
paints which may be used, and by checking the qualities of deliveries, paint failures
have been reduced to an exceedingly low level. In one or two cases which have occurred
and the trouble has been identified as being due to the use of a paint of unauthorised
composition, the contractor has replaced the work. When it is pointed out that the
annual cost of painting, using nearly a quarter of a million gallons a year, is more than
one million pounds per year the scale of the saving is apparent. Many other instances
could be quoted such as the buying, from tendered goods, of the lowest priced articles
found to be satisfactory on analysis.
The very wide field covered by the work of this branch will be realised from the
succeeding sections and the appreciation of its value by the executive services of the
Council is evidenced by the ever-increasing demand which is being made for its advice
on a vast variety of problems.