1 This International Standard specifies a method for the determination of the refractive index of transparent and light-coloured hydrocarbon liquids such as are used in capacitors, transformers, circuit breakers and in cables of the oil-filled type.
2 This method is applicable to liquids having refractive in-dices in the range 1,33 to 1,7 and at temperatures of 20 to 30 °C. It is not applicable, within the accuracy stated to liquids having colours darker than 4 colour to ISO 2049, or to liquids having bubble points so close to the test temperature that a reading cannot be obtained before substantial deterioration takes place.
NOTES
3 Liquid certified reference materials are available for the range 1,33 to 1,50, but not above this range. The accuracy of the method is not readily checked in the range 1,5 to 1,7.
4 Although measurements may be made at temperatures up to 70 °C, the accuracy of the method under these conditions has not been evaluated.
5 The refractive index of a liquid varies with its composition and with the nature and amount of contaminants held in solu-tion. If the refractive index of an unused liquid is known, deter-minations made on the same liquid after periods of service may form a basis for estimating any change in composition or the degree of contamination resulting from dissolution of extra-neous material. The refractive index may also be used, in con-junction with other physical properties, to assess the hydrocarbon types present in petroleum fractions.