GB749143A - Improvements in or relating to electrode structure - Google Patents

Abstract

749,143. Electrochemical electrodes. BECKMAN INSTRUMENTS, Inc. Jan. 22, 1954, No. 2017/54. Class 37. An electrode structure for electrochemical measurements combines in .one unit the reference half-cell and the measuring electrode, and comprises two coaxial tubular glass members with the annular space between them sealed at the bottom and containing the reference halfcell, and an electrochemically sensitive member attached to the glass tubes below the sealed bottom to form the measuring electrode. As shown (Fig. 1), an outer glass tube 1 with a conical constriction 4, is sealed at the bottom end with a pH-sensitive membrane 2, and supports an inner glass tube 6 formed at the bottom into a cone 8 which fits into the cone 4 of the outer tube 1, and is sealed thereto with a thermosetting silicone cement 9, the inner tube 6 being supported centrally at the top by a rubber ring 14. The tubular portion of tube 6 is covered externally by a layer of silver 10 and silver chloride 11 to form a reference half-cell in conjunction with a salt bridge fluid in the space 13 between the two tubes 1, 6, introduced via a hole 15 normally covered with a rubber ring 16. A liquid junction between the half-cell and the liquid to be tested is formed by a wire 20 of inert metal fused into the side-of the outer tube 1, the difference in thermal expansion rate between the wire and the glass leaving an annular gap; or alternatively an asbestos fibre may be used instead of the wire 20. The measuring electrode comprises a shielded cable with the shielding 27 connected to the silver layer 10 on the surface of inner tube 6, and the central conductor 22 embedded in a pool of solder 23 at the bottom, sealed end of tube 6, into which is sealed a platinum wire 24 extending into the lower portion of tube 1, the external portion being covered with a layer of silver chloride on a layer of silver, and immersed in an ionic reference solution 25 contacting the pH-sensitive membrane 2. In a modification the membrane 2 has a metal coating on its inner surface in direct contact with the wire 24, or the membrane is replaced by a sensitive metal cone shell in direct contact with wire 24, the shell being made of platinum, palladium, gold, silver or antimony. In a modification to the reference halfcell the shielding 27 over the conductor 22 extends to just short of the solder pool 23, with a layer of insulating resin over the end of the shield 27, the protruding insulation 26 and the exposed part of the conductor 22, and the silver, silver-chloride covering on the tube 6 is replaced by a silver wire dipping into the salt bridge fluid in the space 13, in contact with a bead of silver chloride. In another embodiment a temperature-sensitive resistance wire is wound over the exposed portion of the insulator 26 covering the conductor 22, so that the temperature of the cell may be determined. For use at other than atmospheric pressures and at high temperatures, the combination glass electrode 56 (Fig. 6), without the rubber ring 16 over the hole 15, is mounted in a thin-walled stainless steel tube 74, open at the bottom 75, and provided with a hole 76 at or slightlyabove the level of the liquid junction 18.