GB562538A - Improvements in or relating to the electrical determination or control of the amountof oxidizing or reducing substance in liquids - Google Patents

Abstract

562,538. Determining physical qualities of materials ; liquid resistances. WALLACE & TIERNAN PRODUCTS, Inc. Jan. 26, 1942, No. 1088. Convention date, Dec. 28, 1940. [Class 37] The amount of oxidizing or reducing substances in a liquid is determined by means of an electrode cell apparatus after the addition, to a known volume of the liquid under test, of a predetermined amount of a reducing or oxidizing agent. A system is shown for the determination of the chlorine concentration of water, sewage, or other liquid flowing through a system in which it is treated with chlorine. The water under test flows through a conduit 10 into which chlorine is passed through a pipe 11 from a chlorinator 12 at a rate determined by a differential converter 15 in accordance with the rate of flow of the water in the conduit, the converter being controlled by a venturi . meter 16. For detection of the electrode potential caused by the chlorination, the treated and untreated water is supplied to a double electrode cell 30. This comprises a pair of chambers 31, 32 separated by a porous partition 33. In each chamber is an electrode 35, 36 comprising a downwardly-facing disc of a rare metal, such as gold or platinum. Each chamber includes a venturi nozzle 37, 38. whereby the flow of liquid is continually introduced and causes abrasive particles to be projected against the electrode surface, as described in Specification 548,173. The nozzles 37, 38 are supplied with liquid under a constant head through pipes 39, 40 from constant level boxes 41, 42. Untreated water is supplied to the box 41 through pipes 47, 48 and treated water is similarly supplied to the box 42 through pipes 49, 50. The pipes 47, 49 are connected by a pipe 51 containing a normally closed valve 52, valves 53, 55 in the pipes 47, 49 being normally open. Untreated water may be supplied to both chambers of the cell for calibration by closing the valve 55 and opening the valves 52, 53. A reducing agent of known concentration is fed from constant-feed devices 63, 64 through pipes 67, 68 into the pipes 39, 40 that feed the untreated and treated water to the two compartments 31, 32 of the cell. A predetermined quantity of reducing agent is thus maintained in each compartment of the cell. Suitable reducing agents are o-tolidine, hydroquinone, ferrooyanides of potassium, sodium, barium, &c., ferrous chloride and sulphate, cuprous salts, and organic derivatives that have oxidation potentials in the same range as hydroquinone. The voltage generated at the electrodes 35, 36 is applied to a recording potentiometer 59 having contacts for starting and stopping a motor 20 in either direction so as to serve as a fine adjustment on the differential converter 15 controlling the flow of chlorine from the chlorinator 12. In a modification, a cell of the electrode depolarization type described in Specifications 548,173, 548,174 and 562,537 may be employed. Only the treated water is supplied to this type of cell through a constant level box, reducing agent being fed to the sampled liquid as it leaves this box. Specification 367,821 also is referred to.