A new design on solution density measurement described as the magnetic weigh method (MWM) is introduced. Inline solute concentration can be determined based on the definite relationship to the density of the solution. Several seed crystals have been used for crystallization in the study. The variances of excess saturation ratio S recorded by MWM show that seed crystals start to grow remarkably at S = 0.13 and the crystallization rate is in proportion to S in spite of the crystal surfaces enlarged simultaneously. The ratio of linear and parabolic growth rates initially is analyzed to be approximately 3:2 and at low supersaturated concentration, the mechanism of the growth of crystal is deduced as diffusion and transport adsorption at the growing surface. (C) 2002 Elsevier Science B.V. All rights reserved.