An insulating end cap for a cylindrical electrolysis cell the type comprising at least two tubular electrodes with a cylindrical membrane arranged co-axially between them, comprises a first annular section with first and second axial ends, having at its first axial end a circular seating or one end of an outer cylindrical electrode and at its second end a circular aperture, of smaller diameter than the circular seating and co-axial therewith, to accommodate one end of the membrane. A second annular section of the end cap is detachably secured to the first and has a central circular aperture of smaller diameter than the central aperture of the first section and co-axial therewith, to accommodate one end of the inner cylindrical electrode. The two part construction of the end cap facilitates the assembly of the cell, and reduces the likelihood of breakage of the fragile ceramic membrane.