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the RI
oil
of a “pure crude” (Goual and Firoozabadi, 2002; Taylor et
al., 2001; Buckley, 1999; Buckley et al., 1998). Namely, RI
oil
is
found by an extrapolation of the experimental data to a volume
fraction of 100 %, in accordance with mixing rules. A best fit of
Eq. (1) to our data points (coefficient of determination R
2
= 0.995),
shown by a solid line in Figure 1, provided a value of RI
oil
= 1.4785
for the studied crude. In a number of publications it has been
stated that RI correlates with density and with an asphaltene con-
tent of a crude oil. We have compared the RI of our oil with RIs for
45 crudes of various origin (Yang et al., 2002; Buckley and Wang,
2002; Goual and Firoozabadi, 2002; Buckley et al., 1998). Our re-
sults appear to be in a reasonable agreement with previously pub-
lished data. There is good overall correlation of RI with oil’s den-
sity (R
2
= 0.76), though a correlation of RI with asphaltene content
is much worse (R
2
= 0.29).
Fig. 1. Refractive index for a wide range of oil concentrations in toluene.
Solid line - the ideal mixing rule (Eq. 1).
2.3. “History Effects” in Dilute Oil Solutions
Studies of solutions with oil content below ≈1 vol. % revealed
strong effects of the “history of oil dissolution in toluene”. When
the above technique of sample preparation was employed, the re-
sults have shown poorly controlled dependencies on such factors as
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