The features of liquid media investigation during express control using the phenomenon of refraction are considered. The advantages of using the differential method for investigation of liquid media in comparison with the others are noted. The features of liquid media investigation with using the differential method are established. A new technique for liquid media investigation has been developed, which allows changing the discreteness of the scale for measuring the refractive index n in the range from 1.2300 to 2.230. The design of the Anderson differential cuvette has been developed for carrying out research with required accuracy, by changing the discreteness of the measurement scale n. The results of experimental investigations of liquid media (water and water with iron oxides) are presented.