A method of assembling an electrolytic membrane cell is disclosed. The method includes the steps of conditioning the membranes with a conditioning fluid, assembling a vertical stack of horizontal electrode frames with a horizontal membrane sheet between each pair of frames, applying pressure to vertically compress the vertical stack, rotating the compressed vertical stack from a vertical orientation through approximately 90.degree. in which orientation of the stack is called a "pack", connecting the pack into an electrical circuit and to raw material supply lines and product withdrawal lines and then electrically operating the pack while maintaining the pack in a horizontal orientation.