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The British Standards Deposit Gauge collects the liquid (usually entirely
rainwater) and solids falling in an accurately measured area of little less
than one square foot. A monthly analysis of the contents of the gauge deter
mines the amount of soluble and insoluble deposit and the total solids
deposited. The results are expressed in terms of grammes of deposit per 100
square metres or in tons per square mile. This method of measurement does in
general give auseful indication of the extent of pollution by deposited matter.
The Lead Peroxide Instrument is a small cylinder coated with lead peroxide and
exposed to the air, although protected from rain. The sulphur dioxide in the
air reacts with the coating to form lead sulphate (Pb + SO2 = Pb SO4) which is
determined by analysis after a suitable period of exposure. the analyst's
findings are expressed as "milligrammes of sulphur trioxide fixed per day per
100 square centimetres of Batch "A" standard lead peroxide." By the use of
this method it is possible to compare the intensity of pollution of the air by
sulphur at different places and times.
Samples from the Council's two stations are sent to the Council's Public
Analyst at monthly intervals and the results of the analyses are reported to
the Public Health Committee and also sent to the Director of Fuel Research, the
Department of Scientific and Industrial Research, Fuel Research Station, East
Greenwich. That Department publishes a monthly "Bulletin" in which are
reported the results of analyses from all stations throughout the country. A
table of monthly findings from the three Stations in Hackney is given on Page
20 of the Appendix.

The Volume tric Sulphur Dioxide Instrument consists of an electrically
operated air pump which draws a measured quantity of air through a test tube
containing a solution of hydrogen peroxide which retains the sulphur in a form
suitable for determination by titration with alkali. The sulphur dioxide combines
with the hydrogen peroxide to form sulphuric acid (H2 O2 SO2 = H2 SO4).
The amount of alkali needed to neutralise the sulphuric acid is measured and
the average concentration of sulphur dioxide during the period under test is
then calculated by reference to a formula. Measurement of the concentration
of smoke in the atmosphere is made by inserting a filter paper between the air
intake and the test tube. Air passing through the filter paper produces a
stain the shade of which is dependent upon the amount of smoke in the
atmosphere. Once a day, or at such other intervals as may be appropriate, the
filter paper is changed and the "shade value" of the stain assessed by comparing
it visually with a set of standards. The smoke concentration is calculated
from the shade value and the quantity of air passed.
The readings and the necessary calculations are made daily, excluding
Sundays. These also are sent to the Department of Scientific and Industrial
Fuel Research and reported in the "Bulletin".