Interferometric technique for measuring the refractive index variation of a liquid with temperature

A technique for measuring the variation of refractive index of a liquid as a function of temperature or solute concentration using a Mach-Zender interferometer is described. The principal difficulty of obtaining a uniform temperature along the optical path in the sample liquid while simultaneously varying the temperature at a reasonable rate is overcome by heating the liquid in a separate vessel and injecting the heated fluid into the test vessel as a series of jets to encourage turbulent mixing. An equivalent resolution in the refractive index variation of 2×10^-6 was obtained. The above method was used to determine the variation of refractive index in a 0.1% NaCl/H₂O solution in the temperature range 23°-33°C.