is passed along line 35 to a ph compensation cell 36 the ph compensation cell 36 has a ve electrode 38 and a ve electrode 39 provide therein the ph of the electrolyte 22 flowing through the ph compensation cell 36 is raised by the evolution of h 2 gas the hydrogen gas so produced is permitted to escape through a vent 37 provided in tank 32 the h 2 gas is liberated via decomposition of water leaving behind oh ions to compensate for the h ions generated at the ve electrode an alternative ph compensation cell for use on the ve electrolyte side is shown in fig3 b in this embodiment cell 36 39 is provided with a ve electrode 38 39 and a ve electrode 39 39 the cell is divided into two compartments 41 and 42 by means of a microporous membrane separator 40 the h 2 produced by the decomposition of water may be vented directly from cell 36 39 by means of vent 43 thus making vent 37 on tank 32 redundant in the ph compensation cell br 2 is generated at the ve electrode and h 2 is produced at the ve electrode thereof the overall reaction being referring to fig3 a the bromine merely dissolves in the ve electrolyte and becomes available for discharge the.