A Use for Broken Glass Electrodes One of the shortcomings in student use of a pH meter in acid-base titrations is the occasional breaking of the tip of the glass electrode. Cautions, warnings, and even threats never seem to insure against the momentary carelessness that rams the electrode against the hottom of the beaker or turns the magnetic stirrer on full blast, causing the stir bar to strike the electrode tip. However, once broken, the electrode can still be used as an indicator electrode for a potentiometric precipitation titration of silver or halide ions. Merely remove the remnants of the broken dass tin and the exoosed silver wire is readv for use. (As is usual in these titratians.. vieorous stir.. rrng is necessary lo inaure cquil>brium, particularly near the equi\.almre point. Also tun ur three rntnurcs at:rrml: may be rcqulred with each addition of titrant., Mhpn necessary depmrrs of i l w r tmlldc ran he remwed hy dippmg the electrode :n 1 : l nmlc arid for a few mnmern,, then rinaing with water and wiping with a tissue. This technique provides an interesting contrast to the usual Fajans, Valhard, or Mahr methods for halide ions as well as offering e use of potentiometry for something more than the usual pH titration. John E. Davidson Eastern Kentucky University Richmond, Kentucky 40475
Volume 50, Number 5, May 1973 / 375
