- Refractometry
Refractometry is the method of measuring substances'
refractive index (one of their fundamental physical properties) in order to, for example, assess their composition or purity. Arefractometer is the instrument used to measure refractive index ("RI"). Although refractometers are best known for measuring liquids, they are also used to measure gases and solids; such as glass and gemstones.The RI of a substance is strongly influenced by temperature and the
wavelength of light used to measure it, therefore, care must be taken to control or compensate for temperature differences and wavelength. RI measurements are usually reported at a reference temperature of 20 degreesCelsius , which is equal to 68 degreesFahrenheit , and considered to be room temperature. A reference wavelength of 589.3 nm (thesodium D line) is most often used. Though RI is a dimensionless quantity, it is typically reported as nD20, where the "n" represents refractive index, the "D" denotes the wavelength, and the 20 denotes the reference temperature. Therefore, the refractive index of water at 20 degrees Celsius, taken at the Sodium D Line, would be reported as 1.3330 nD20.Refractometers are frequently used by grape growers and
Kiwifruit growers forBrix testing ofsucrose levels in their fruit. Refractometry is also used in thegelatin industry. To convert the RI of a gelatin sol (reported in Brix) to a gelatin concentration, one need only multiply by eight-tenths (0.8). A sol with a 10.0 RI would therefore be 8% gelatin by weight. This is known to be a reliable conversion for gelatin sols as low as 1% up to over 50%.Types of refractometers
There are four main types of fluid refractometers:
traditional handheld refractometer s,digital handheld refractometer s,Abbe refractometer s, andinline process refractometer s.External links
* [http://www.gemstonebuzz.com/instruments/refractometer.html#refractometry Refractometry - Gemstone Buzz] methods for measuring refractive index.
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