Abstract: The invention concerns a process and apparatus for the preparation of a disinfectant for water, such as drinking- or swimming-water by electrolysis of an aqueous NaCl-containing solution.In order to improve these, the process of the invention is characterized in that an NaOCl-containing solution obtained by electrolysis is enriched with electrolytically obtained Cl.sub.2 by either electrolytically preparing an aqueous NaCl and NaOCl-containing solution and further electrolyzing said solution to partially convert the Nacl still present therein into Cl.sub.2, or electrolytically preparing a mixture of an aqueous NaCl solution and Cl.sub.2, and further electrolyzing said mixture to partially convert the NaCl still present therein into NaOCl.

Abstract: Method and apparatus for electrolyzing halogen salt solutions having a low halogen salt concentration with direct formation of halogen, using an electrolytic cell comprising at least one anode and at least two electrodes which can function as cathodes. The anode is permanently connected as an anode, a portion of the anodic current is passed through one electrode which can function as a cathode, and a cathodic current is passed through the other electrode which can function as a cathode. The polarity of the electrode functioning as a co-anode and of the electrode functioning as a cathode is periodically changed in cycles of 80-330 minutes.