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18
Sulphur dioxide by the lead peroxide method. The difference between the deposit gauge
and the lead peroxide instrument is that the former collects sulphur dioxide which is washed
out of the air by rain or deposited in any other way, whilst the other collects it by a chemical
process. Table I gives the results obtained during the year at Golden Lane and Finsbury Circus.
At Golden Lane there is an increase of 0.32 mg./lOO sq.cm./day compared with the average
of the previous five years, whilst at Finsbury Circus there is a decrease of 0.14.
Volumetric estimation of smoke and sulphur dioxide—-Tables 11 and III. The average daily
concentrations of smoke and sulphur dioxide are conveniently measured with this apparatus. A
description of the instrument was published in a previous annual report.
Smoke. At Golden Lane the average for the year was 14 parts per 100 million parts of air.
The figure has remained constant for the past three years, although it slightly exceeds the
average for the previous five years. The results for Cloak Lane and Snow Hill follow a pattern
similar to that of Golden Lane, but those recorded at Bishopsgate have been influenced by the
proximity of the railway termini at Liverpool Street. The concentrations at Bishopsgate are
much in excess of those recorded at the other three stations.
Sulphur dioxide. The concentration of sulphur dioxide is slightly below the average of the
previous five years at Golden Lane. Similar results have been obtained at Cloak Lane and
Snow Hill, but at Bishopsgate the figures for nine months are considerably in excess of those
at Golden Lane which covered a period of 12 months."