240
A. NELSON-SMITH
of this effect are not to be found in the literature. Spencer (1967) found
that mud in an Essex estuary was warmed through 5-6°C during tidal
exposure in late summer, raising the temperature of the returning sea
water by about 1°C.
C. Detection and identi$cation
liuman senses can detect surprisingly low concentrations of petroleum oils. Melpolder et al. (1953) found that a very sensitive nose can
detect 0.005 p.p.m. of gasoline (motor spirit) in cold water, receiving a
" strong odour " from 0-01 p.p.m. Ineson and Packham (1967) quote
the even higher sensitivities of 0.00005 p.p.m. for motor spirit (with
additives) and 0.0005 p.p.m. for diesel oil, although heavier fuel and
crude oils are detected only at 0.2-25.0 p.p.m. Oily taint in fish and
other sea-foods or in drinking water can presumably also be detected
at these levels. An oil-film 4 x 10-5 mm thick (corresponding to
about 0.04 ml/m2) is just visible in the most favourable of normal
lighting conditions (Stroop, 1930 ; American Petroleum Institute,
1963). Dangl and Nietsch (1952) claim that 0.01 p.p.m. of mineral oil
can be detected by blue fluorescence at the meniscus of a sample under
ultra-violet light, although the specificity of this test has been questioned (see Ineson and Packham, 1967). I n the field, oil-slicks invisible
to the eye can be recorded from the air by infra-red colour photography (Cowell, 1969a). It is also possible to distinguish an oil-film from
the effects of wind, fish-shoals or floating debris which sometimes
resemble a slick. The necessity for processing the film involves a delay,
but the technique may prove useful for the enforcement of antipollution legislation. A simple field-test was reported by Weir (1964),
who discovered that kerosine contaminating a drinking-water supply
stopped the active movement of a small piece of camphor dropped on
the water surface. Camphor also moves actively on clean sea water and
is completely arrested by a film of crude oil at the lower limits of
visibility.
A rapid method which can determine less than 0.1 p.p.m. of petroleum oils in water is the combustion of a small water sample in oxygen
(van Hall et al., 1963). Inorganic carbon is first removed by acidifying
the sample. The gases evolved are passed over heated cupric oxide and
carbon dioxide is determined in the gas-stream, using an infra-red
analyser. It should be remembered that the technique determines all
organic carbon and is not specific to hydrocarbons. Webber and Burks
(1952) stripped light hydrocarbons (C, and below) from water in a
stream of carbon dioxide. Melpolder et al. (1953) were able to include
all those boiling below 200°C by passing hydrogen through a water
A. NELSON-SMITH
of this effect are not to be found in the literature. Spencer (1967) found
that mud in an Essex estuary was warmed through 5-6°C during tidal
exposure in late summer, raising the temperature of the returning sea
water by about 1°C.
C. Detection and identi$cation
liuman senses can detect surprisingly low concentrations of petroleum oils. Melpolder et al. (1953) found that a very sensitive nose can
detect 0.005 p.p.m. of gasoline (motor spirit) in cold water, receiving a
" strong odour " from 0-01 p.p.m. Ineson and Packham (1967) quote
the even higher sensitivities of 0.00005 p.p.m. for motor spirit (with
additives) and 0.0005 p.p.m. for diesel oil, although heavier fuel and
crude oils are detected only at 0.2-25.0 p.p.m. Oily taint in fish and
other sea-foods or in drinking water can presumably also be detected
at these levels. An oil-film 4 x 10-5 mm thick (corresponding to
about 0.04 ml/m2) is just visible in the most favourable of normal
lighting conditions (Stroop, 1930 ; American Petroleum Institute,
1963). Dangl and Nietsch (1952) claim that 0.01 p.p.m. of mineral oil
can be detected by blue fluorescence at the meniscus of a sample under
ultra-violet light, although the specificity of this test has been questioned (see Ineson and Packham, 1967). I n the field, oil-slicks invisible
to the eye can be recorded from the air by infra-red colour photography (Cowell, 1969a). It is also possible to distinguish an oil-film from
the effects of wind, fish-shoals or floating debris which sometimes
resemble a slick. The necessity for processing the film involves a delay,
but the technique may prove useful for the enforcement of antipollution legislation. A simple field-test was reported by Weir (1964),
who discovered that kerosine contaminating a drinking-water supply
stopped the active movement of a small piece of camphor dropped on
the water surface. Camphor also moves actively on clean sea water and
is completely arrested by a film of crude oil at the lower limits of
visibility.
A rapid method which can determine less than 0.1 p.p.m. of petroleum oils in water is the combustion of a small water sample in oxygen
(van Hall et al., 1963). Inorganic carbon is first removed by acidifying
the sample. The gases evolved are passed over heated cupric oxide and
carbon dioxide is determined in the gas-stream, using an infra-red
analyser. It should be remembered that the technique determines all
organic carbon and is not specific to hydrocarbons. Webber and Burks
(1952) stripped light hydrocarbons (C, and below) from water in a
stream of carbon dioxide. Melpolder et al. (1953) were able to include
all those boiling below 200°C by passing hydrogen through a water