METHOD AND DEVICE FOR MEASURING REFRACTIVE INDEX

PROBLEM TO BE SOLVED: To provide a method and a device for measuring a refractive index capable of highly accurately measuring the refractive index of a colloid liquid.SOLUTION: The lower plane of a dielectric transparent flat plate 30 which has a higher refractive index than a colloid liquid 33 and whose upper plane is parallel to the lower plane thereof is brought into contact with the surface of the colloid liquid 33, the lower plane of a Dove prism 32 whose upper plane is parallel to the lower plane thereof is brought into contact with the upper plane of the dielectric transparent flat plate 30 through a matching liquid 38, P-wave light having a narrow spectral width which is suitable for refractive index measurement is made incident on one slope face of the Dove prism 32, an incident angle is obtained which is minimized in intensity of non-scattered reflection light from the interface between the lower plane of the dielectric transparent flat plate 30 and the surface of the colloid liquid 33, and based on the incident angle , a refractive index nof the dielectric transparent flat plate 30, a refractive index nof the Dove prism 32, and a refractive index nof gas in contact with the Dove prism, a refractive index nof the colloid liquid 33 is obtained.