\As reported in many previous publications, the cross section shape of prism solids will maintain the original square or become round after a certain duration of dipping and corrosion in certain melts. This paper gives theoretical explanations for these phenomena. Based on the deduction of the Laplace equation, it is found that for the solid-liquid system with contact angle (0) smaller than 90degrees, the maximum height of liquid surface on the lateral faces (H-f) is greater than that at the prism edges (H-e) before corrosion. If the corrosion and dissolution of the solid sample reduce the liquid surface tension, the case of H-f > H-e will be maintained or intensified due to the larger extent of dissolution at the edges, and the down-and-up motion of the liquid surface on the prism will mainly occur on the lateral faces, resulting in the maintenance of the original square shape of the sample's cross section. However, if the dissolution of the solid sample increases the liquid surface tension, the case H-f < H-e will possibly occur, and the up-and-down motion of the liquid surface on the prism will principally occur at the edges during ascent and on the lateral faces during descent, transforming the cross section shape of the sample from the original square to round due to the dominant corrosion of the ascending flow. For systems with theta > 90degrees, the liquid surface height exhibits the opposite direction, and the evolution trends of the cross section shape are similar. (C) 2003 Elsevier Inc. All rights reserved.