Characterization of aqueous rubidium chloride as an equitransferent ultraconcentrated salt bridge

From e.m.f. measurements on the concn. cells Ag|AgCl|RbCl (m)‖RbCl (mf)|AgCl|Ag and Rb-amalgam|RbCl (mf)‖RbCl (m)Rb-amalgam, the ion and solvent transference nos. have been detd. for aq. RbCl solns. at molalities up to 7 mol kg-1 over the temp. range from 25 to 55°C. From the ionic transference nos. found, aq. RbCl emerges as the most closely equitransferent salt bridge ever characterized. Considering also its high soly. (7.8 mol kg-1 at 25°C), RbCl is recommended as a built-in salt bridge for ref. electrodes, in view of replacing the insufficiently equitransferent KCl bridges so far adopted by manufacturers.