GB690701A - Improvements in and relating to the determination, recording or control of impurities, especially oxygen, in industrial gases, or in liquids - Google Patents

Abstract

<PICT:0690701/III/1> The amount of a component of a gas mixture is automatically determined and recorded by feeding an electrolyte solution, capable of absorbing and reacting with the component, at constant head through a special orifice in vessel 1, via cooling zone 2, to conductivity cell 3, mixing it (e.g. in coils 6 61) with the gas to be tested, leading the solution via a second cooling zone 12 to second conductivity cell 13 connected in a Wheatstone network with the other cell, and using the electromotive force developed across the bridge (or the change in resistance necessary to balance the bridge) to record the amount of the component present. The special orifice is circular, and has frusto-conical convergent inlet and divergent outlet ducts, and a knife edge of thickness not exceeding 5/1000 inch. The cross-section of the cooling zones and conductivity cells has a breadth: length ratio of not more than 1 : 3, and preferably 1 : 5 to 1 : 10. Gas is fed to the apparatus at constant rate from inlet 7 via capillary flowmeter 8 and capillary tubes 11, 111 to the coils. In one form of electrical circuit Fig. 2. (not shown), the two cells are in parallel in the Wheatstone network, the other arm including standard and variable resistances; output from the bridge passes through a rectifier to a recording ammeter. In an alternative arrangement, Fig. 5, (not shown), the cells are in series, the resistance of both arms of the bridge may be varied, and the bridge system is connected to a self-balancing recorder, which may be of the electronic type. A mechanical valve controlling the supply of the component to the gas mixture may be operated by the output from the bridge through a relay. In the determination of oxygen, e.g. in commercial carbon dioxide, an aqueous solution of chromous sulphate containing hydrochloric acid is preferably used as the electrolyte; also suitable are solutions of vanadium, cobalt, and molybdenum sulphates. The chromous sulphate solution may be prepared by reacting sulphuric acid in an inert atmosphere with metallic chromium and a small piece of a more electropositive metal, e.g. zinc or aluminium; the solution is filtered, diluted, and stored under carbon dioxide. Carbon dioxide may be determined in gas mixtures using aqueous caustic potash, sulphur dioxide using a solution of bromine and sulphuric acid, and carbon monoxide by preliminary oxidation to carbon dioxide; other gaseous components which may be measured are hydrogen sulphide and ammonia. The oxyenf content of boiler feed water may be measured by expelling oxygen from the water, and mixing it with an inert gas. Specification 641,978 is referred to.