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35
The "total soluble matter" though greater in some cases and less in others on
comparing 1949 with 1948, was generally less than that of the pre-war period
averages.
This brings us to the "total solids" probably the most important figure of
this series. Generally for 1949, in localities where this figure was high it showed
some decrease as compared with that for 1948 (e.g. Archbishop's Park, Battersea
Park, South Kensington). In districts where it was low there was a small increase
(e.g. Kew). Battersea Park remained the worst situation with Archbishop's Park
next on the list.
The difference between the London results and those of the two out-county gauges
at Kew and Godalming is noteworthy, the total deposits for these being much less
and, in turn, that at Godalming was less than that at Kew. The variations over the
years on these "total solids" are more clearly shown graphically in Figure 1 for
five stations, four in London and also that at Kew. The fluctuations are so different
in the various cases that it is not possible to summarise shortly, though on the
whole there was a tendency towards reaching a minimum in 1939, with, in most
cases, a subsequent rise, which was particularly marked at Battersea Park up to a
maximum in 1947.
The "Sulphates" were generally lower in 1949 than in 1948, and, on the
whole, than those for the average of previous periods of years.
Method (b) — This method measures the amount of sulphur gases "fixed"
by a cylinder of oxidising material exposed in air for a period of one month. The
result may be taken to be an indication of the "activity" of the sulphur gases
and thus is specially useful in considering effects on buildings, etc., for which
purpose the method was originally devised. It is a more recent one than the deposit
gauge dating as it does only from 1935.
Table 40, p. 147, shows the averages for some of the stations operated during
1949, these being yearly averages of the monthly results. The figures are expressed
as S03 milligrammes per 100 sq. cms. per day. Considering first the average for
the selected five stations: it will be seen that the average figure for 1949 was the
lowest of the series of years so far examined, except for 1940 and 1941 during the
war (see Figure 2 also). The average for the five year period 1945-9 was, however,
slightly greater than that for the wartime period 1940-4, but less than that of the
immediate pre-war quinquennium. Figure 2 shows the variation of the average
results of these five stations throughout the years during which they have been
operated, and also that for the country district of Godalming for comparison. In
the former, the minimum at 1940 is well marked and is followed by a rising
tendency to a maximum at 1944-5 with a subsequent slight fall: it should be
pointed out that these stations have been specially selected for the comparison
because they are all situated in parks and so removed from immediate local pollution.
The effects of this last mentioned factor are again evident (Table 40) in
considering the County Hall figures as obtained at different points on the roof:
with the prevailing S.W. wind the S.W. corner gets air direct from the river
without local contamination, whereas the other two points may be affected by gases
from the heating plant chimney. The particularly high figures at Beckton are
noteworthy: this station is at the Council's Northern Outfall Works and is situated
immediately between the largest gas works and the largest electricitv generating
station in this country, which fact no doubt accounts for the bad atmospheric
conditions and the notoriously great corrosion of metal and paintwork which occurs
in this area. The very low figures for the country district outside Godalming are
significant of the difference in this respect between the air of such a neighbourhood
and that of an industrial town.
Method (c) — The Volumetric method measures the actual amount of sulphur
dioxide in a known volume of air taken at an even rate during the period of the