refractometer

A refractometer is an optical instrument used to measure the refractive index of a liquid or translucent solid. It operates on the principle that light changes direction when crossing boundaries between media of different optical densities, as described by Snell's law. In practice, many refractometers determine either the refractive index directly or a derived scale such as concentration or sugar content.

There are several designs. Handheld devices typically use a transparent prism with a sample well; light is shone through the sample and the refracted light is read on a scale. More precise laboratory models, such as Abbe refractometers, use two prisms and calibrated scales. Digital refractometers use sensors and electronic readouts. Instruments may be designed for liquids, pastes, or solids; materials include glass or sapphire prisms; temperature compensation may be built in.

Measurement often requires placing a drop of sample on the prism, closing a cover, and observing the boundary between light and dark or reading a digital index. Calibration normally uses a reference substance, commonly distilled water at a specified temperature (often 20 degrees Celsius) with a known refractive index (near 1.0000) or standard calibration solutions.

Applications span food and beverage to determine sugar content and quality; petrochemicals and solvents to assess purity; gemology and mineralogy to estimate refractive indices of gemstones; clinical and biological analysis to study fluids. Refractometer readings can be affected by temperature, sample quality, and instrument alignment, so proper calibration and temperature control are important.