Measure using a suitable refractometer.
A sodium lamp may be used to provide the light source at a known wave-length (589.6 nm) although many instruments are corrected for daylight use.
||BS 684 Section 1.2
|Significance of result
|Used to determine the purity of an oil, as adulteration can be readily detected. The refractive index of an oil reflects its degree of unsaturation. In general, the higher the refractive index the greater the degree of unsaturation or conjugation.
||Usually quoted at 20°C for liquid oils or 40°C for solid fats