This paper presents an analytical and experimental investigation of the new ground-based method for diffusion measurements in liquid metals presented in the two companion papers. The configuration under consideration is a horizontal capillary tube submitted to a vertical steady magnetic field; the temperature field is assumed isothermal. The aim of this third part is to introduce a single description of transport in a diffusion experiment over a wide range of parameters (namely magnetic field intensity and experimental duration), which overlaps both the two asymptotic models previously presented. The experimental results, obtained in two different apparatus, are in good agreement with the analytical model and exhibit a fair repeatability. The impurity diffusion coefficient of Bi in Sn is measured at 275 degreesC and near the fusion point, in good agreement with recent microgravity data. (C) 2003 Elsevier Ltd. All rights reserved.