Abstract: Mediaeval iron rivets were immersed in a bath of 0.05 M NaOH - 0.5 M Na2SO4 at 64°C. The extracted Cl- was determined in a system (illustrated) in which the flow-through component was arranged in a two-line configuration and contained the indicating Cl--sensitive electrode and a constant-potential reference electrode. A calibration graph, prepared by using standard solution containing 5, 10, 20, 50, 100, 200 or 500 ppm of Cl- and different amounts of NaOH and Na2SO4, was rectilinear for >30 ppm of Cl-, but determinations of 5 to 30 ppm of Cl- by using the curved part of the graph could also be achieved. Fifty samples could be analyzed in 1 h under optimum conditions.