Abstract: Disclosed is an electrolysis cell and method of operation in which metal anodes (preferably titanium) provided with an electrically conducting electrocatalytic coating in an anode compartment face diaphragm covered metal cathodes in a cathode compartment, in which the anodes are spaced from an imperforate valve metal separating partition by a separating wall behind which the anolyte can recirculate downward, the anodic gases rising in the anode compartment "gently" circulate the anolyte and the gases are discharged into a brine box above the anode compartment near the center thereof and the anolyte recirculates downward near at least one end of the anode compartment; and a method of operation which provides circulation from front to back of the anode compartment and from center to sides of the anode compartment and means for adding new diaphragm material to the circulating anolyte to deposit said new diaphragm material on the diaphragms and methods of determining when and how much new diaphragm material to ad