  This paper presents a diffusion experimental study for ternary
lysozyme-Na$_2$SO$_4$-water system, from moderate precipitant concentrations
into the supersaturated region and provides a complete set of four diffusion
coefficients. These data are important in order to provide accurate models of
protein diffusion with applications in growth of protein crystals for X-ray
diffraction studies. All three-component mutual-diffusion experiments reported
here were performed by Rayleigh interferometry at pH$=4.5$, T$=25^o$ C and at a
mean lysozyme concentration (average of top and bottom solution concentrations)
of 0.6 mM (8.6 mg/mL). Four experiments, with different combinations of protein
and Na$_2$SO$_4$ concentration differences, were performed at each of five mean
Na$_2$SO$_4$ concentrations (0.1, 0.25, 0.5, 0.65 and 0.8 M), for a total of 20
experiments. In addition, we have measured dynamic light-scattering diffusion
coefficients of the ternary system lysozyme chloride-Na$_2$SO$_4$-water.
