Definition
The velocity of light varies with density of the medium through which it passes.Thus when light passes from a less denser medium such as air into a more dense medium water it is bent or refracted. The magnitude of this bending when expressed as a ratio of sines of the angles of incidence and refraction of the light, is the refractive index. It is designated by the letter n.
n =sin i/sin r
Where i = angle of incidence
r = angle of refraction
n=refractive index constant
Refractive index of milk and ghee: Refractive index of milk has a range between 1.3440 to 1.3480. The refractive index of water at 20 0 C with the D line of sodium = 1.33299. The refractive index of material such as spectrum (589.3 mm) is n(d) 20 milk is higher than water due to dissolved material in milk. The dissolved material includes salts, lactose, etc. The refrecture index is used to measure the concentration of dissolved solids like sugar in food industry e.g. jams, jellies, syrups, etc., to estimate sugar. A butyro refractometer (B.R. Index) reading between 40-42.5 is the index of purity of ghee. Ghee exhibiting a refractive index of 1.4545 corresponds to a B.R. index of 43 at 40 0 C.
Measurement of Refractive Index
i)Immersion refractometer: It is used for measuring refractive index of milk.Milk serum is prepared with the help of copper sulphate. The proteins are removed by filtration. A drop or two is placed on the prism of refractometer and the refraction is measured
ii) Abbe’s refractometer: Abbe’s refractometer is a modified version of refractometer. It is provided with a narrower range for measuring RI for fats and oils. There is an arrangement for circulation of water so that fat remains in a melted state and temperature can also be controlled. The scale is usually graduated in numbers (e.g. 43 which corresponds to n = 1.4545). Abbe’s refractometer is used to measure purity of ghee. A drop or two of ghee drop -lets are placed on the surface of Abbe’s refractometer prism, which is heated at 40 0 C through water circulation. The refractometer reading called as butyro refractometer reading (B.R) is recorded on the scale. A B.R reading between 40-42.5 is taken as the criteria for purity of ghee. This is commonly known as the B.R. index of ghee. An increase in B.R. shows the adulteration of ghee with vegetable oil/animal body fat.
Refractive index is used to measure
The velocity of light varies with density of the medium through which it passes.Thus when light passes from a less denser medium such as air into a more dense medium water it is bent or refracted. The magnitude of this bending when expressed as a ratio of sines of the angles of incidence and refraction of the light, is the refractive index. It is designated by the letter n.
n =sin i/sin r
Where i = angle of incidence
r = angle of refraction
n=refractive index constant
Refractive index of milk and ghee: Refractive index of milk has a range between 1.3440 to 1.3480. The refractive index of water at 20 0 C with the D line of sodium = 1.33299. The refractive index of material such as spectrum (589.3 mm) is n(d) 20 milk is higher than water due to dissolved material in milk. The dissolved material includes salts, lactose, etc. The refrecture index is used to measure the concentration of dissolved solids like sugar in food industry e.g. jams, jellies, syrups, etc., to estimate sugar. A butyro refractometer (B.R. Index) reading between 40-42.5 is the index of purity of ghee. Ghee exhibiting a refractive index of 1.4545 corresponds to a B.R. index of 43 at 40 0 C.
Measurement of Refractive Index
i)Immersion refractometer: It is used for measuring refractive index of milk.Milk serum is prepared with the help of copper sulphate. The proteins are removed by filtration. A drop or two is placed on the prism of refractometer and the refraction is measured
ii) Abbe’s refractometer: Abbe’s refractometer is a modified version of refractometer. It is provided with a narrower range for measuring RI for fats and oils. There is an arrangement for circulation of water so that fat remains in a melted state and temperature can also be controlled. The scale is usually graduated in numbers (e.g. 43 which corresponds to n = 1.4545). Abbe’s refractometer is used to measure purity of ghee. A drop or two of ghee drop -lets are placed on the surface of Abbe’s refractometer prism, which is heated at 40 0 C through water circulation. The refractometer reading called as butyro refractometer reading (B.R) is recorded on the scale. A B.R reading between 40-42.5 is taken as the criteria for purity of ghee. This is commonly known as the B.R. index of ghee. An increase in B.R. shows the adulteration of ghee with vegetable oil/animal body fat.
Refractive index is used to measure
- Total solids in milk and condensed milk
- Sugar content
- Purity of ghee
- Adulteration of milk with water
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