Results ob"tined from the continuous operation of a two inch-diameter column crystallizer and scale-up considerations involved in the design of a four inch column are presented. Implications of a mathematical model for continuous column crystallizers are discussed, including countercurrent flow of reflux liquid phase and crystal phase, leading to a reduction in salt concentration in liquid adhering to the crystal. The factors discussed include speed of crystal transport and superimposition of oscillatory motion, column length and attitude, feed location in coIumn and the effect of product to feed ratio. Variations in crystal rate are considered and diffusion and mass transfer coefficients calculated. A Y, -Impurity content of feed stream (M M-r). YP -Dehned by Eq. (2) (M M-r). u, -Impurity content of stripped stream (M M-r). y.P -Impurity content of reflux liquid at the feed point (M M-l). Z -Distance in the column measured from the freezing section (L). 2, -Distance of feed point from the freezing section (L). Greek symbols Q -.Ratio of adhering liquid stream to crystal rate. & -Impurity content of solid phase (M M-l). 5 -Volume fraction of free liquid.