Refractive index as a function of wavelength for sixty API-NBS hydrocarbons

Abstract

Measurements of the refractive index at 20°, 25°, and 30 ° C and at se ven wavelengths, from 6678.1 to 4358.3 Angstrom units , were made on 60 purified hydrocarbons of t he API-NBS series. The apparatus consisted of a precision Abbe-type refractomcter, calibrated by m eans of NBS Standard Samples of hydrocarbons certified with respect to refractive index at thc th ree tcmperatures and seven wavelengths uscd. The light SOU l'ces used were a mercury arc, a sodium vapor lamp, and h ydrogen and helium discharge tubes, w ith suitable filL er. A constant t empe rature bath maintained the te mpe rature of the refractomete r prism s constant within ± 0.02° C. The experimental daLa on the hydrocarbons were adjusted by m ean s of a four constan t Hartmann equation , nA=n ",+C/(A-A*) 1.6, and a two constant modified Cauch y equation , fln, =a+ b/ X2• (fln)., t he change in t he refracti ve index a t t he wavele ngth, A, when the t e mpem t ure is chan ged from 20° to 25 ° C or 25° t o 30° C, is used instead of n, of the Cauchy eqllation). The compu ted refractive index a L 20°, 25 °, an I 30° C, t oge Lher with the values of t h e specific di spers ions, and the constants of the HarLmann and m odified Cauchy equat ions, applicable over the ran ge of m ea l11'e ment, a re rep or ted for 60 API-NBS h yd rocarbo ns, comprising 17 paraffins, 14 alkylcyclop entanes, 8 alkylcyclohexanes, and 21 alky lbenze nes.