Patent GB-706519-A (GB)
Title: Improvements in or relating to electrochemical apparatus
IPC: G01N27/30
Filed: 1951-11-19
Abstract: 706,519. Determining physical qualities of materials. BECKMAN INSTRUMENTS, Inc. Nov. 19, 1951 [Jan. 23, 1951], No. 27075/51. Class 37 Apparatus for the electrochemical testing of liquids subject to varying pressure comprises a salt-bridge tube reference electrode with facilities for obtaining equal pressures inside and outside the salt-bridge tube by means of an immiscible fluid in pressure transfer relationship with the liquid. The complete apparatus consists of a sealed vessel 12 (Fig. 1) containing the liquid 13 to be tested, which may be static or flowing, and a slidable rod 17 carrying the electrical assembly 16 which is connected by leads 35, 37 through the rod 17 to a pH meter 36. The measuring electrode 25 (Fig. 2) and reference electrode 26 are protected by an assembly comprising an upper and lower plate 21, 24 supported by a number of roads 22. The measuring electrode 25 comprises a bulb 27 blown on a glass tube 28 below a restriction 29, a second tube 30 being sealed at 29 inside 28 and containing a half-cell contact 31 of the type described below. The lower portion of tube 28 and bulb 27 is filled with an electrolyte 32. The complete assembly is supported in a mounting 34 attached to the upper plate 21. The reference electrode 26 comprises a saltbridge tube 40 (Fig. 3) having a wide upper part 43 and narrow lower part 41 with a liquid junction 42 at the bottom consisting of a wick 45 of fibrous material, the tube being filled with an electrolyte 47 up to an opening 48. The upper part 43 contains a half-cell structure 50 comprising a glass tube 51 sealed at the top to tube 43, and containing at its bottom end a silver-silver chloride half-cell 55 comprising a tube 100 (Fig. 5) of inert metal, e.g. platinum, connected to a spring conductor 56, containing a plug 104 of silver and a quantity of silver chloride 106, the bottom of the tube 100 having an opening 108. The silver-silver chloride may alternatively be added on an external part of a platinum wire (Figs. 7 and 8, not shown). The half-cell structure 50 may alternatively be a calomel half-cell made by providing a constriction 119 (Fig. 9) in the tube 51, filling the lower part with mercury 121 covered with a calomel body 122, and a mass of glass wool 123 up to the constriction 119. A platinum wire 120 dips into the pool of mercury 121, ionic communication being provided by a hole 124. The tube 51 may be of plastic material, or an inert metal, e.g. platinum. The complete reference electrode 26 is secured to mounting means 62 with screwed joints and gaskets 66, 69, 70 to provide a seal against inflow of liquid 13. The salt-bridge tube 40 is surrounded by a further tube 75 open at the bottom 77 to allow the liquid 13 to enter the space 76 between the two tubes, and containing a hole 80 in line with the hole 48 in the tube 40 to permit the initial filling of tube 40 with the electrolyte 47, the holes 80, 48 being covered by a wide rubber band 81. Thus when the reference electrode is lowered into the liquid 13 a column of air is trapped in the space 76 which transfers the external pressure to the electrolyte 47. Gases other than air may be used, or other fluid media, and may be replenished by means of a tube 90 communicating with the space 76, and through a pipe 94 to a container 97 through a valve 98. The electrochemical half-cells of the measuring and reference electrodes comprise the subject-matter of the claims of Specification 706,549.