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December, January and February when compared with that for the months of June,
July and August gives some idea of the amount of pollution from domestic sources
which, although responsible for more than one half the total smoke in the air
are producing practically no smoke at all during the summer months
Taking the average readings for sulphur for the summer three months as 1.89
compared with the four winter months when the average was 5.18, this shows a
nearly threefold increase during the winter, the cause of which must be apportioned
almost entirely to domestic smoke
Most industrial plants are capable of careful control, use and adjustment,
and of burning smokelessly and as a result of co-operation with industrial users
a fair degree of smokelessness has been achieved Industrial smoke is of a different
nature from domestic smoke. In industrial furnaces the temperature of combustion
is so much higher under the controlled conditions of burning that all the
volatile constituents af the coal are distilled readily in a relatively short
time. If there is sufficient secondary air admitted with sufficient turbulence to
mix intimately with the "green" gas distilled off it will be completely oxidised
and it will all burn off without smoke. If, however, turbulence is lacking or
the quantity of secondary air is inadequate some of the gases will not be oxidised
but will be "cracked" this is converted by reduction at the high temperature to
molecular carbon the presence of which gives rise to the characteristic dark quality
of industrial smoke in badly fired furnaces normally never seen emitted from
the normal domestic chimney.
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