Refractometers
4. Refractometers. These are instruments used to determine the refractive index of liquids or solids (one of the most important constants in determining the purity of a substance). They mainly consist of a prism system, viewing oculars, reading oculars, and a temperature control device (as it strongly affects the refractive index). They are especially widely used in the food industry (for checking vegetable oils, butter and other fatty substances, analysis of jams, fruit juices, etc.), in the glass industry, on oil refineries, in biology (for measuring protein content in blood plasma or effluents, etc.).
Most refractometers are mounted on a base or stand; others are hand-held types or may be designed for mounting on walls of production tanks.
Source: "Explanations to the Harmonized System of Foreign Economic Activity of the Russian Federation (HS FEA Russia)" (prepared by the Customs Committee of the Russian Federation) (volume 4, sections XVI - XXI, groups 85 - 97)