The evolution of liquid-solid systems by phenomena such as dissolution, nucleation, growth and agglomeration, is often described by means of only two variables : concentration of dissolved species and mean radius of the solid grains. But such a simplification may mask some important physical phenomena and is inadequate with models for which the knowledge of the size distribution is absolutely necessary. The correlations between the different kinds of results obtained from the use of three experimental techniques, possibly both being used simultaneously in the same reactor, make possible a more precise knowledge of the evolution of the liquid-solid system. Some examples of the use of these three techniques (conductometry of the liquid phase, turbidimetry, and sizing of particles by laser beam scattering) are presented for the water-potassium sulphate system.