A separating element for separating the bottom part of an electrolytic tank from the rest of the tank space in connection with the removal of solids settled on the bottom of the electrolytic tank, said separating element being installable in the electrolytic tank and removable therefrom along a path formed by support and control members arranged in the electrolytic tank. If the data embedding condition is satisfied, the apparatus embeds optional data in the encoded voice code by replacing a second element code with the optional data. The simplification of data allows for a localized measure of regional pattern density determination in much less time than conventional techniques. The upper drive means at the cover frame have driving pinions which can be driven around a vertical axis and which can engage into racks at the upper side of the mould segment halves such that a vertical offset is possible, for example as a consequence of thermal expansion, between the mould segment halves and the driving pinions.