GB851512A - Improvements in or relating to the determination of oxygen by electrical methods - Google Patents

Abstract

851,512. Determining physical qualities by electric tests. BRITISH OXYGEN RESEARCH & DEVELOPMENT Ltd. May 12, 1959 [May 29, 1958], No. 17184/58. Class 37 A method and apparatus for determining the concentration of oxygen in an electrolyte comprises charging a pair of electrodes immersed in the electrolyte to a predetermined potential, interrupting the charging and determining the fall of potential of the negatively. charged electrode after a given time interval, the fall of potential being proportional to the concentration of oxygen in solution in the electrolyte. Fig. 1 shows a gas analysis cell comprising a glass vessel 10 in which are mounted a positive standard reference electrode 15, for example a silver/silver chloride electrode, sealed within a tube 17 and a negative electrode 18 formed by the tip of a thin platinum or gold wire 19 also sealed with a glass tube 20. The cell is filled with an oxygen free electrolyte, for example 0À1 N potassium chloride solution and the gas fed in through tube 23 bubbles through the electrolyte and leaves at passage 14. The electrodes 15 and 18 are protected from flow disturbances by glass cylinders 21 and 22 surrounding them. The cell E is connected in a circuit as shown in Fig. 2 in which a condenser C is charged from a constant E.M.F. source B to a voltage as indicated by meter V. After a predetermined charging period switch S disconnects the charging circuit and connects it across cell E. After a given discharge period switch S is operated to reconnect the charging circuit and disconnect the condenser C from the cell E. Whilst the condenser is being recharged the negative electrode discharges slowly and the fall of potential at the end of this period is measured by voltmeter V and is proportional to the oxygen content of the gas which has been passed through the electrolyte. In the modified circuit shown in Fig. 3 a reference condenser Cr of low capacity is connected in parallel to the cell E during the discharge of the main condenser C so that both the electrodes of the cell and the condenser C r are charged to the same constant potential. Voltmeter M is connected in series with the cell E and condenser C r and measures the difference in potential between the negative electrode and the negative plate of the condenser Cr. The difference in potential between the electrodes and the reference condenser being indicative of the concentration of oxygen in the gas. The determination of the oxygen content of a static atmosphere may be made by use of a modification of the cell as shown in Fig. 4. The negative electrode is formed by the end of a platinum wire 26 and the positive electrode by a silver wire 28 which runs along the outside of glass tube 27 and forms a ring about its end. A disc 29 of filter paper moistened with a suitable electrolyte is fitted at the end of the tube and held in contact with the electrodes by a sheath of plastic film fitted over the end of the tube and held by a ring 31. The electrodes are placed in the static atmosphere and connected to circuits as described in connection with Figs. 2 and 3 the fall in potential of the negative electrode being measured and being proportional to the concentration of oxygen in the static atmosphere.