A COMPACT CALOMEL ELECTRODE EDWIN H . SHAW, J R . Unimrsity of South Dakota, V e r m i l i o n , S o u t h Dakota
THE calomel electrode shown in the accompanying figure1 has proved quite convenient for electrometric titrations with the quinhydrone electrode, especially in
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Drafting by courtesy of Professor H. E. Brookman.
titrations a t small volume. The vertical arrangement of the parts saves space in the titration assembly, which must include the two electrodes, a buret, and a stirrer. The addition of potassium chloride is controlled by a pinchclamp, the ring-sealed'jet permitting observation of the rate of addition. Electrical contact with the calomel cell is made through the inner tube, the platinum wire being included in the solid seal a t the bottom. Since the apparatus includes a platinum seal, i t should be made up in soft glass, but pyrex glass may be used if the platinum wire is beaten thin and a bead of pyrex glass is melted on it and pressed down iirmly. This bead is then fused onto the flared inner tube before making the solid seal. The body of the cell may be made in any convenient dimensions, from 13 by 50 mm. to 22 by 125 mm. The delivery tube, which is pictured straight in the diagram, may be bent into any convenient position. A shorter platinum electrode may be mounted by means of a cork to the lower portion of the delivery tube, in which case the calomel cell may be protected in the intervals between use by a vial of potassium chloride. Calomel electrodes of this design are not as easily broken as the conventional Hildebrand model, because there is only one projecting side tube, and this tube may be fastened to the body of the cell with cork and wire. Measurement of pH may be made with samples as small as one ml. and titrations are readily carried out on 50-ml. samples. In two years of service, this calomel electrode has proved very rugged, stable, and convenient.
