For approximate quantitative estimations, drop oil into reagents
as described above and let remain at room temperature 5 min. In
meantime, cool 10 mL portion absolute ether in ice-H2O. After
5 min, place test tube containing oil and reagents in ice-H2O 1 min,
add cold ether (taking care that no H2O falls into test tube), and mix.
Return tube to ice-H2O bath and let colors develop while it is immersed
in ice-H2O. Colors develop slowly and reach maximum
within ca 5 min.