Comprises an inverted “U” tube with its ends closed by sintered discs. For use in experiments involving the measurement of cell EMF under conditions of forward, zero and reverse current flow. The bridge comprises an inverted “U” tube with its ends closed by sintered discs. This apparatus provides a more effective method of making reversible cells then the wet filter paper or agar gel methods. Dia. of arms 13mm, overall width 80mm, overall height 100mm.