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It is interesting to note that the amount of pollution follows the
general "line" of the visibility. The periods of observations are those
of 24 hours in each week, and are generally made between 10 a.m.
Thursday and 10 a.m. Friday.
(4) Measurement of Sulphur Activity.—The type of apparatus in use
has been designed by the Department of Scientific and Industrial
Research, and gives an indication of the activity of sulphur compounds
in the atmosphere. The apparatus consists of a porcelain cylinder around
which is bound a piece of fabric impregnated with lead peroxide. This
cylinder is exposed to the atmosphere for a period of one calendar
month, and sulphur gases which come in contact with it change the
lead peroxide into lead sulphate. According to the amount of gaseous
sulphurous impurities present, the amount of lead sulphate formed will
vary, and from this data can be assessed the injurious effect of such
impurities on building materials.
Three of these cylinders were installed during the year, one at the City
Hall, one at Mount Street Gardens, Mayfair, and one at the Coroner's
Court, Horseferry Road. Records have been obtained since March 1st,
and are shown in the following table.