It is shown that the ionic content of the suspending medium is of importance in determining the velocity of sedimentation of particles in the micron size range.Calculations are made for the effect of electroviscosity on the rate of separation of particles by the sedimentation method, and it is concluded that in extreme cases it may not be possible to separate particles differing in size by up to 25%.The elimination of the electroviscous effect in sedimentation analysis is discussed, and it is shown that the effect can generally be eliminated by carrying out the sedimentation in a moderately concentrated electrolyte solution.