# Barometric law for hard sphere sedimentation

by KayDee01
Tags: barometric, sedimentation, sphere
 P: 12 So I have the equation for Barometric law in terms of density as: $\frac{\phi(z)}{\phi_{0}}$=exp($-g.M.z/R.T$) where R=Universal gas constant, z=height of sedimentation, T=Standard temperature, g=Gravitational acceleration, M=Molar mass. When this equation is used to calculate the height of the universe, the molar mass is the molar mass of the atmosphere. But if you're using it to calculate the height of a colloid sedimentation when you have a colloid solution, is the molar mass referring to the mass of the colloid, the average mass of the colloid and solvent, or the relative mass of the colloid (i.e. buoyant mass of the colloid in the given solvent)?? This isn't a homework question, I'm just wondering what factors are being taken into account when calculating the height of a colloid sediment.