Temperature correction of the sample
The refractive index of all samples will vary with temperature. If it is required to know the
refractive index of the sample at 20
°
C, then either the instrument must be controlled at 20
°
C, as
described below, or a correction value for the sample must be added to the scale reading.
The correction value will vary considerably with the type of sample. Glass samples have a low
temperature coefficient, water based products are higher and oils and chemicals generally greatest.
Typical (and very approximate) values are:
Sample
Temperature coefficient: Change in index /
°
Celsius
Glass +0.00001
Water
-0.00010 (-0.07
°
Brix)
50% sucrose sample (50
°
Brix) -0.00017
(-0.08
°
Brix)
Edible oil
-0.00040
Correction values for sucrose solutions measured on the Brix (% Sucrose) scale are shown in the
table below. The correction values should be added to the scale reading.
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