In the electrolytic production in water of insoluble metal hydroxide from the metal thereof, more especially of coagulant ferric hydroxide from iron, rectangular channels with flanking ribs provide for pre-established, uniform spacing of the electrode plates and intermediate binary wiping structures. Electrolytic current contact is protected against corrosion by a metallic embossment on the plates. Binary reciprocating wipers are at different wiping levels between successive plates and reversely directed to the opposite surfaces thereof. The wipers are urged against the plate surface by bilateral springs, as the surfaces recede due to thinning of the plates as they are consumed. Terminal panels, on which the wipers land after a reciprocating stroke, coextensively bound the plates; protuberances facilitate the transit of a wiper between them. The terminal panels may be employed to concurrently generate oxygen or chlorine as a supplement to coagulant ferric hydroxide. An electrode plate is described that is stabilized against end corrosion.