  We investigate the experimental limits of validity of the Stokes-Einstein
equation. There is an important difference between diffusion and
self-diffusion. There are experimental evidences, that in the case of
self-diffusion the product D /T is constant and the equation is still valid.
However, comparison of existing experimental data on viscosity and diffusion
coefficients D of small, fast moving ions unambiguously show that the product D
/T depends strongly on temperature T. The temperature dependence of diffusion
coefficient declines from that of viscosity. Therefore, the Stokes-Einstein
equation is not valid in this case.
