Refractometer Refractometers are optical instruments used to determine the percentage of soluble solids in a liquid solution. To do this, the refractometer uses the principle of total refraction of light (caused by the type and concentration of substances dissolved in a liquid solution, for example, sugar), which takes place in the boundary layer between the prism and the shows. The refractive index of the prism determines the upper limit of the measurement range, since this must always be greater than that of the sample. The refractometer therefore measures the density of liquids, the denser a liquid the greater the refraction.


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  • 1 History
  • 2 Refractometry
  • 3 Limits of use
  • 4 Unit of Measure (BRIX)
  • 5 Sources


Refractometers were invented by Dr. Ernst Abbe, a German / Austrian scientist in the early 20th century. The Abbe refractometer is the “grandfather” of all modern refractometers, thanks to its simple operation and reliability, it still has a place in laboratories. There are two types of refractometers depending on the detection of the refractive index; transparent systems and reflection systems. Portable refractometers and Abbe refractometers use transparent systems, while digital refractometers use reflection systems.


Refractometry is called the optical method of determining the speed of light propagation in a medium / compound / substance / body, which is directly related to the density of this medium / compound / substance / body. To use this principle, the refraction of light is used, ((which is a fundamental physical property of any substance), and the measurement scale of this principle is called the refractive index. Refractometers are the instruments that use this principle of refraction either the refraction, (using several prisms), or the critical angle, (using only one prism), and its primary measurement scale is the refractive index, from which the different specific scales are built, Brix (sugar), Specific Density,% salt, etc. Refractometers are used to measure in liquids,

Limits of use

The Abbe refractometer can only be used for liquids whose refractive index is lower than that of flint glass (n = 1.7). Beyond this value, the rays close to the grazing ray would undergo a total reflection, which would make the measurement impossible. This limitation is not an impediment in practice, since few liquids have a reflection index higher than that of flint glass. The index varies depending on the temperature. A thermostat system, consisting of a circulation of water within the optical system, allows this effect to be regulated.

Unit of Measure (BRIX)

The Measurement Scale (%) shows the concentration percentage of the soluble solids contained in a sample (water solution). The content of soluble solids is the total of all solids dissolved in water, including sugar, salts, proteins, acids, etc., and the measurement read is the total of the sum of these. Basically, the Brix percentage (%) is calibrated to the amount of grams of sugar contained in 100g of sugar solution. Thus, when measuring a sugar solution, Brix (%) must be perfectly equivalent to the actual concentration. With solutions containing other components, especially when one wants to know the exact concentration, a conversion table is necessary.


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