A new method for measuring the refractive index of liquid media using a triangular cuvette has been developed. The features of goniometric measurements of the refractive index of liquid media using a triangular cuvette with a right angle have been determined. A cuvette design has been developed for conducting long-term studies of refractive index changes over occupied volume, which is particularly relevant for hydrocarbon mixtures. The advantages of the developed method for measuring the refractive index over industrial refractometers are highlighted. The main ones are the ability to easily measure liquid media of varying transparency and to conduct long-term measurements of volatile media. The results of studies of various media are presented and compared with measurements on industrial refractometers.