GB1122432A - Improved electrolytic titration apparatus - Google Patents

Abstract

1,122,432. Electrolytic titration apparatus. DOHRMANN INSTRUMENTS CO. Nov. 11, 1965 [Nov. 18, 1964 No. 47864/65. Heading G1N. In an automatic titration apparatus, titrant is generated electrolytically by a pair of generating electrodes until the end point, as determined by a sensing electrode and reference electrode, is reached. The electrolyte 12 is contained in a glass vessel 13 having a sample inlet tube 18 and a pair of drain tubes 22, 23. A removable helical reference electrode (34) is vertically disposed in tube 32 and is in contact with the electrolyte 12 through a porous plug (39), Figs. 6 and 7 (not shown). The generating cathode (46) is a horizontally disposed helix in drain tube (23) (behind tube 22), Fig. 5 (not shown). The generating anode (52) and sensing electrode (51) are flat rectangular electrodes sealed to the top 16 of the vessel. The measuring circuit includes synchronized choppers A, B to isolate the sensing and reference electrodes from the generating electrodes. In operation, ganged switches S1 to S5 are set to calibrating positions 2 and 3 for measuring the bias potential and electrolytic potential respectively to enable resistor R1 to be adjusted so that the bias potential is equal and opposite to the electrolytic potential. The sample, e.g. a gas in an inert carrier gas, is introduced through inlet tube 18 and the switches are set to position 4. The potential difference between the sensing and reference electrodes, less the bias potential, is passed via synchronized choppers A and B through an amplifier A1 to a measuring bridge and recorder 64 and also to the generating electrodes. The end point is reached when sufficient titrant has been generated to bring the input to amplifier A1 to zero. If the end point is passed, a negative potential is applied to the generating electrodes to consume the excess titrant. The recorder has a centre control R15 and a marking switch 68 to produce a swing of the recorder pen to mark a point on the recorder chart. For a silver titration, the reference electrode (34) is silver in saturated silver acetate, the generating cathode is platinum, the generating anode and sensing electrode are silver and the electrolyte 12 is 70-80% acetic acid. For an iodine titration, the reference electrode 34 is platinum in saturated tri-iodide, the other electrodes being of noble metal and electrolyte 12 is 0À05% potassium iodide and 0À4% acetic acid.