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35
was decided to adopt, so far as possible, the breakpoint system of chlorination
whereby the dosage applied is sufficient to ensure a residual of true free chlorine (as
distinct from " combined " chlorine in the form of chloramines). By this procedure
the polluting nitrogenous matter derived from bathers is quickly destroyed by
oxidation and the water is kept chemically pure as well as bactriologically sterile.
A considerable investigation was carried out as to the necessary changes at existing
plants to implement this decision and the best method of operating them. Methods
and demonstrations on water testing were given to bath attendants. The water of
natural ponds used for bathing was also tested.
Samples of soil were analysed as to their content of plant nutrient substances and
new types of plant pots were examined as to their suitability for use, having regard to
Dorositv. frost resistance, etc.
The materials examined for this service covered a very wide field and many of
them are dealt with in other paragraphs concerning the services which use them; for
example, paints and building materials for housing, and insecticides for public health.
Foods of all types formed a considerable proportion of the total; they were examined
(a) to allocate contracts ; (6) to check the quality of deliveries ; (c) to investigate
complaints ; and (d) to assess whether new preparations are of potential use in the
service and are offered at a fair price. Generally a high standard of quality was
maintained with but few justifiable complaints. Particular attention was again given
to canned foods in regard to corrosion of the container and possible tin content of
the food.
Supplies
A careful watch was kept on the quality of the liquid milk supplied for use by the
Council in its various services and samples of condensed and dried milk were also
examined in the Council's laboratories and generally found to be satisfactory.
Chemicals, drugs and medical supplies of various types were submitted for
analysis and report, and also lubricating and other oils, floor and other polishes, soaps,
scouring powders, etc. Many of these are supplied to the Council's specifications.
The position in regard to synthetic detergents was closely watched during the
year and many proprietary preparations were examined. The use was continued of
the type previously found by trial to be the most satisfactory for hand washing-up
in kitchens. Disinfectants were examined as to their germicidal value, stability of
emulsion and freedom from staining linen fabrics.
Swimming bath waters and drinking water supplies at residential schools were
examined and the work on school meals already described was done indirectly for
this service. In the case of the swimming baths at premises of both the Education
and Children's departments the water treatment has been by a system of improvised
chlorination. The Council, however, agreed in principle to a recommendation that
treatment plants should be installed at these baths in order that they shall operate
on the "breakpoint" chlorination system already mentioned, instead of the present
less efficient improvised process. Having regard to existing circumstances, the
construction of such plants will naturally have to be spread over a considerable
period. Advice was also given on the treatment of swimming bath water at summer
camps.
Education
and Children
riastic articles tendered tor use as ieeding utensils tor intants were examined as
to their suitability; they were tested from the utility angle, such as strength and
resistance to heat, and also for the possibility of toxicity. Plastic wood suggested
for use as a modelling material was considered to be unsuitable primarily because of
its formaldehyde content.
Instructional visits of school parties to both the Headquarters and Northern
Outfall Works laboratories should also be mentioned.
Work in connection with this service increased, particularly on the advisory side,
for instance, in regard to the use of fire-resisting coatings and materials. A few of
the special investigations made were :—(a) the cause of a fire was ascribed to steel
Fire Brigade