New low-index liquid refractive index standard: SRM 1922

A new standard for the calibration of refractometers has been developed. St andard Reference Material (SRM) 1922 is a mineral oil with a refractive ind ex n(D) = 1.46945 at 20 degrees C, which is within the range of the Brix sc ale (% sucrose). The change in refractive index with temperature (dn/dT) ha s been characterized for the range 15 degrees C to 35 degrees C to allow fo r calibrations within that range of temperatures. The refractive indices we re measured at 5 wavelengths in the visible spectrum by using the method of minimum deviation with a +/- 2-3 x 10(-5) uncertainty at 20 degrees C. The values of n(D) and dn(D)/dT were determined by fits of a two-term Cauchy f unction to the values at the measured wavelengths with a +/- 6 x 10(-5) unc ertainty in n(D) at 20 degrees C.