Patent GB-748775-A (GB)
Title: An improved apparatus for continuously determining small amounts of one gas in another
Inventor: BARLEY THOMAS
IPC: G01N21/78
Filed: 1953-05-08
Abstract: <PICT:0748775/III/1> <PICT:0748775/III/2> Apparatus for determining the proportion of a gas present in another comprises an absorber unit in which the mixture of gases is contacted continuously with a solution that absorbs the gas to be determined and changes colour or depth of colour as a result, means for supplying solution and the gas mixture to the absorber unit at controlled rates, and means, which as described are photo-electric, for continuously measuring and recording the colour changes of that solution.  The absorbing solution, or where a mixture of solutions is used, the separate components pass from aspirators (not shown) through glass wool filters and cold water jackets to calibrated drip pipes which deliver them to a mixing chamber.  The mixing chamber is heated and the solution leaving it is cooled to remove dissolved air and other carrier gas.  The solution then passes through line 1 to a cell 2, where the colour of the solution can be observed visually.  This solution then passes through a cell 3 forming part of the photo-electric recording apparatus, a control tap 4 and capillary restrictors 5, 6 at the top of the absorber unit 8 (see below) where the indicator solution is brought into contact with the mixture of gases to be tested.  The component to be tested for is now absorbed by the liquid indicator, while the carrier gas passes away through tube 15.  The liquid leaving the absorber is heated and cooled by jackets 9, 10 to remove dissolved gases and then passes to a second cell 11 of the photoelectric indicator where the difference of colour between the indicator after contact with the gas stream and that before contact is measured.  Finally the liquid passes through a second visual observation cell 13, the colour of the liquid in which may be compared with that in cell 2 by means of filters.  The photo-electric system for comparing the liquid in cells 3 and 11 may be as described in Specification 638,740 [Group XL(b)], in which two photo-cells connected in adjacent arms of a Wheatstone bridge each receive light reflected from the mirror of a shunted galvanometer. The beam is of such width that the light reaching one cell has passed through the reference solution while that reaching the other has passed through the sample.  The cell masked by the analysing solution is always wholly illuminated but that masked by the reference solution is variably illuminated in accordance with galvanometer deflection.  In use difference in the two light beams unbalances the bridge, the unbalance voltage being amplified and used to drive a servomotor which operates a slide wire to shunt the galvanometer and rebalance the bridge and operate a pen mechanically coupled to the movable slide wire contact.  The absorber (Fig. 2) comprises an upper distributing head which the liquid enters through tube 23 and the gas through tube 24.  Gas pressure then forces the liquid through a capillary 22 into a lower distributing head 21 which allows liquid to enter equally three capillary tubes 25 arranged at the corners of an equilateral triangle.  Each tube then opens into an ellipsoidal container 8 over the inner surface of which the liquid runs while the gas makes contact with the ellipsoid then merging into a further capillary and so on.  The carrier gas finally escapes through tube 15, and the indicator liquid is heated and cooled by jackets 9, 10. Dimensions of the chamber are given in the specification.