Electrical cell

969, 608. Electrolytic testing apparatus. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Dec. 22, 1961 [Dec. 30, 1960], No. 44756/60. Heading G1N. In an electrolytic arrangement for measuring the amount of oxygen in other gases, the cell comprises three electrodes, two of which (one platinum, one silver), are not attacked by the electrolyte in the presence or absence of oxygen, and one, (lead), which is attacked in the presence of oxygen, and the flow of current to, the last named is kept down by taking a major proportion of the current through the silver electrode to the platinum. In Fig. 3 the silver, lead, and platinum electrodes 9, 18, 35, are connected respectively to the emitter, base and collector of a transistor 30 the currents to the lead and platinum electrodes being (1/1 + B). Ie and (B/1 + B). Ie, respectively where B is the transistor gain and Ie is the current through the silver electrode. In an alternative arrangement described with reference to Fig. 5 (not shown) the current to the lead electrode passes through the control windings of a balanced pair of saturable reactors, the output windings of which include a bridge rectifier having the silver and platinum electrodes connected across its D.C. diagonal. A balancing resistor is included in the A.C. input circuit. The cell comprises a moulded resin container 1 Fig. 1, in which the test gas is admitted from an inlet 4 through a non-return valve 5 and passes down the central bore of a tube 8 to a space 10 below an electrode 9, comprising silver discs mounted to form a helical passage and in good electrical contact with a porous polythene tube 12, mounted on a raised portion 2 of the casing and dipping into the electrolyte 17. The gas after passing through the helical passage is bubbled through the electrolyte by means of a tube 15 and is lead off via a pipe 24. A lead (Pb) electrode 18 mounted on a rod 19 is dipped into the electrolyte together with a platinum electrode not shown which is also encased in porous polyethylene. The nature of the electrolyte is dependent on the nature of the gas containing the oxygen, and suitable alkaline electrolytes given are potassium hydroxide, sodium hydroxide, sodium and potassium carbonates, and bicarbonates. Dilute sulphuric acid may be used for an acidic electrolyte, or an alkali metal chloride as a neutral electrolyte. Noble metal electrodes may be silver, silver plated nickel, gold, gold plated nickel, indium plated nickel platinum, or even nickel itself. Bas