AbstractThis paper gives some fundamental data which are necessary for the growing of crystals of potassium acid phtalate. The solubility of that phtalate, the values of critical supersaturation of its solutions in water and in solutions containing 0–15% of glycerine and the values of crystal growth rates of the {111} and {001} faces are given. The growth rates R were measured in 10% glycerine solutions of various values of supersaturation (Δa) and of various values of the solution flow rate (v). The saturation temperature was 33 – 35°C. The dependence ofR(111)on the supersaturation Δα and the flow rate v was expressed by the equation\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log }\hspace{1pt}R_{\left({111} \right)} = a* + b_1^* {\rm log }\hspace{1pt}\Delta a + b_2^* \log\hspace{1pt}{\rm v} $$\end{document}The values of coefficientsa*,b*1,b*2were calculated by means of the least squares method. The coefficientb*1corresponds to the formal kinetic order, its value was 1.79 for 0.3 ≦ Δa≦ 1.25 and 6 ≦v≦ 22. – The values of growth rates of basal faces (001) may be obtained when using the value of ratioq=R(111)/R(001). The measurements of growth rates were made in crystallizer of the circulation type and in solutions containing 10% of glycerine to prevent the defect or parasitic growth and the tw