The Uses of a Refractometer

Refractometers measure the refractive index of liquids, solids or gases through which light can pass. A light ray changes direction, or bends, when it enters a material in which the velocity of light is different than in air, the extent of this refraction being directly related to the refractive index. Consequently, a refractometer is a non-invasive device for the identification and characterization of substances. Among other applications, refractometers find use in vision care, veterinary medicine, the study of gems and in the wine and beer making industry.

Vision Care

• Refractometers are used for testing eyesight.

  Optical refractometers are used for eyesight testing and the prescriptions of glasses. Visual acuity depends on the sharpness with which light is focused on the retina. If the liquids in the various chambers of the eye are not uniform in their optical properties because of trauma, age or some other reason, light is refracted as it travels along the optical system of the eye, causing a lack of focus and the related visual impairment. Determining the refractive characteristics of key components of the eye with a refractometer helps in vision correction.

Veterinary Medicine

• Veterinarians use refractometers.

  Simple hand-held refractometers have been widely used by veterinarians since the early 1960s for the measurement of proteins in blood serum and density of urine of farm animals. The refractometer method enjoys the advantages of ease-of-use, rapidity of analysis and low cost. Refractometer analyses compare quite well with those obtained by more cumbersome and complex methods, such as the biuret method.

Gems

• The refractive index of diamond is higher than for any other substance.

  For gemologists it is necessary to determine, first, whether a gem is authentic and then to determine its quality. Refractometers are used to identify gems and verify their authenticity. There is a unique refractive index associated with every type of gem: diamond has the highest refractive index--not only for a gem but for any substance--of 2.42 whereas the topaz refractive index is 1.64. The refractive index for a vacuum is 1.

Wine-Making

• Sugar content of grape juice is measured by a refractometer.

  A refractometer can be used to measure the sugar level in juice to help determine whether it is ready to be made into wine since the initial sugar level may not be sufficient to produce the desired alcohol level in the finished wine. The refractometer reading can be converted into the Brix scale, which is the measure widely used in wine-making. Refractometers require a much lower test volume, just a few drops, than other methods of determining the Brix level. Similar refractometer tests for sugar content are also used in beer-making.