The evolution of convection pattern during the solidification of a binary mixture of ammonium chloride and water in a rectangular chamber was investigated experimentally. The solidification was carried out under a constant coolant temperature of -20 degreesC along the vertical walls of the test chamber. The convection patterns were obtained with the particle image velocimetry technique. The temperature distribution in the chamber was measured with a thermocouple rake. The initial concentrations of ammonium chloride ranged from 10 to 22 wt.%. The present paper presents detailed description of the transient evolution of the convection pattern during the solidification process.