GB1098992A - Electrolytic titrator - Google Patents

Abstract

1,098,992. Electro-physical measurement. INTERNATIONAL STANDARD ELECTRIC CORPORATION. April 30, 1965 [May 4, 1964], No.18248/65. Heading G1N. Continuous automatic titration apparatus, for monitoring noxious vapours e. g. sulphur or hydrazine compounds from propellants, and which electrolytically generates its own titrating agent, comprises a three electrode cell 10 through which gas (e. g. air) to be monitored is bubbled. The sensing electrode S is maintained at a small negative P. D. (below 1À1 volts to avoid hydrogen generation); the generating electrode G is connected to the positive supply, and the reference electrode R through a controlled switch to the negative supply, so that using e.g. hydrobromic acid as the electrolyte, bromine is generated at the generator electrode G increasing the conductivity between electrodes S, G, so that the control signal is reduced and the switching circuit disconnects the supply to electrode R. As bromine is used up, voltage across electrodes S, G, increases to energize the switch and complete the R, G, circuit. In practice the circuit cycles rapidly producing a series of current pulses in the RG circuit Fig. 3 (not shown) whose average value indicates the concentration of the noxious substance. A transistor switching circuit, with ganged range charging switches and a mains/battery power-pack is illustrated in Fig. 2 (not shown). Alternative cell constructions are illustrated in Figs. 4... 6 (not shown) each comprising a container with a vertical tubular cell having the electrodes S, G, R arranged one above the other (S at the top). The gas to be monitored is bubbled in at the bottom of the cell tube, and circulates the electrolyte as it rises. In Fig. 4 the bubbler comprises a conical, wettable glass frit (45) and circulation of the electrolyte from the outer container is restricted by a flow limiting pin (75) in an orifice at the bottom of the cell tube. In Fig. 6 a long spiral sensor electrode (154) is used to increase sensitivity and the electrolyte especially for hydrazine may be 3% potassium bromide, 5% sodium citrate, and 1% citric acid.