0731. Solving a chemistry problem

4. The boundary between the gold hydrosol and the dispersion medium in the centrifugal field of the ultracentrifuge 60 minutes after the start of the experiment was at a distance of 4.35 cm from the axis of rotation, and after 90 minutes - at a distance of 4.43 cm. What is the size of the spherical particles of the hydrosol and what are their specific surface area per unit mass. The rotation speed of the centrifuge rotor is 8200 rpm, the density of gold is 19.3 g/cm3, the density of water is 998.2 kg/m3, the viscosity of water is 1 spz.