Patent GB-565278-A (GB)
Title: Improvements in or relating to determination of the available chlorine content, or changes in such content, of an aqueous liquid
IPC: G01N27/49
Filed: 1943-02-06
Abstract: 565,278. Determining physical qualities of materials. WALLACE & TIERNAN PRODUCTS, Inc. Feb. 6, 1943, No. 2006. Convention date, Feb. 7, 1942. [Class 37] To determine the available chlorine content in an aqueous liquid, the depolarization produced by the liquid upon a polarized cathode exposed thereto is detected while the cathode is maintained at a potential within the range of about - 0.075 to about - 0.2 volt, and preferably between - 0.15 and -0.1 volt, relative to a saturated calomel electrode as standard. The effect of ammonia and ammonia type compounds such as amines, amides and amido acids that may be present is thereby avoided. A system is shown arranged for the automatic control of the application of chlorine to a flowing liquid, such as water or sewage, in accordance with the residual chlorine content of the liquid after treatment. Water flows through a conduit 10 to which chlorine is subsequently added through a pipe 11 by means of a chlorinator 12, chlorine gas under pressure being contained in a cylinder 13 and fed to the chlorinator 12 through a pipe 14. In order to maintain a certain degree of proportionality between the flow of chlorine through the pipe 11 and the flow of liquid through the conduit 10, a differential converter 15 is operated by a venturi meter 16 which creates a pressure differential conveyed by pipes 17, 18 to the converter - 15: This produces a controlling vacuum which is transmitted to the chlorinator 12, for control thereof, by a pipe 19. Water from the main 10 is continuously withdrawn by a pipe 34 to a constant level box 33 and thence passed to a chamber 31 in a depolarization cell 30, an overflow 32 being provided. This liquid is in contact with a perforated cathode 36 in contact with a porous diaphragm 37 which separates the chamber 31 from an upper chamber 40. This contains a saturated solution of potassium chloride in which is an anode formed by a coil of wire 41. A polarizing voltage is applied across the electrodes 36, 41 by means of a circuit including a dry cell 50, regulating rheostat 51, milliammeter 53, and dropping resistor 52, the voltage across which is applied to the electrodes 36, 41 through a dropping resistor 55. A second circuit comprises a dry cell 60, rheostat 61; milliammeter 63, and resistor 62, across which a biassing voltage is developed. A self-balancing recording potentiometer 65 is connected across the resistors 55, 62, the voltage drops across which may be either additive or opposed. Changes'in current produced by changes in depolarization of the cathode 36 are thus converted into voltage changes and is indicated and recorded by the potentiometer 65, which is provided with contacts for controlling a reversible motor 20 controlling the chlorine feed. For measuring the cathode potentiala reference cell 70 is provided and may consist of a saturated calomel electrode, the voltage between the calomel electrode terminal 77 and the cathode 36 being measured by a potentiometer 80. Electrolysis of the water itself may be avoided by using a cathode material having a high hydrogen over - voltage, such as mercury. Specifications 548,18.6, 559,708 and 562,537 and U.S.A. Specifications 1,777,987 and 1,762,706 are referred to.