View source for Refractometer

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A '''refractometer''' is a laboratory or field device used for the measurement of an index of refraction (refractometry). The index of refraction is calculated from the observed refraction angle using Snell's law. For (liquid) mixtures, the index of refraction then allows to determine the concentration using mixing rules such as the Gladstone–Dale relation and Lorentz–Lorenz equation.

==General==
Standard refractometers measure the extent of light refraction (as part of a refractive index) of transparent substances in either a liquid or solid-state; this is then used in order to identify a liquid sample, analyze the sample's purity, and determine the amount or concentration of dissolved substances within the sample. As light passes through the liquid from the air it will slow down and create a ‘bending’ illusion, the severity of the ‘bend’ will depend on the amount of substance dissolved in the liquid.

==Types==
There are four main types of refractometers: traditional handheld refractometers, digital handheld refractometers, laboratory or Abbe refractometers (named for the instrument's inventor and based on Ernst Abbe's original design of the 'critical angle') and inline process refractometers. There is also the Rayleigh Refractometer used (typically) for measuring the refractive indices of gases.

Refractometers are also used in gemology, to help identify gem materials by measuring their refractive index, one of the principal properties used in determining the type of a gemstone. Due to the dependence of the refractive index on the wavelength of the light used (i.e. dispersion), the measurement is normally taken at the wavelength of the sodium line D-line (Na<sub>D</sub>) of ~589 nm. This is either filtered out from daylight or generated with a monochromatic light-emitting diode (LED).

==Availability==
Refractometers can be bought from lab suppliers and online.

Alcohol refractometers, used to measure the concentration of [[alcohol]] can be bought online.

==References==
<references/>
===Relevant Sciencemadness threads===
*[https://www.sciencemadness.org/whisper/viewthread.php?tid=13192 Fine old instruments]
*[https://www.sciencemadness.org/whisper/viewthread.php?tid=158440 Advice for second-hand refractometer condition?]
*[http://www.sciencemadness.org/talk/viewthread.php?tid=72532 Refractometer Range]

[[Category:Lab equipment]]