(Equivalent Test Methods: ISO 5661 and DIN 51423 T2)
EXPLANATION
Refractive index and refractive dispersion are fundamental physical properties which can be used in conjunction with other properties to characterize pure hydrocarbons and their mixtures. This test method covers the measurement of refractive indices, accurate to six units in the fifth decimal place, of transparent and light-colored hydrocarbons that have refractive indices in the range from 20 to 30° C. The test is not applicable within the accuracy stated to liquids having colors darker than No. 4 ASTM color as determined by Test Method ASTM D1500, to liquids having bubble points so near the test temperature that a reading cannot be obtained before substantial weathering takes place, to liquids having a refractive index above 1.50, or to measurements made at temperatures above 30° C.
TEST SUMMARY
The refractive index is measured by the critical angle method with a Bausch and Lomb Precision Refractometer using monochromatic light of an optical-mechanical or automatic digital type with the prism temperature accurately controlled. The instrument is previously adjusted by means of a solid reference standard and the observed values are corrected, when necessary, by a calibration obtained with certified liquid standards.
TEST PRECISION
The bias compared against pure reference materials is not expected to be more than:
Refractive Index: +/- 0.00006
Refractive Dispersion: +/- 0.00012