Patent GB-404660-A (GB)
Title: Means for the analysis of gases
IPC: G01N21/82
Filed: 1932-06-13
Abstract: <PICT:0404660/III/1> <PICT:0404660/III/2> In gas analysis apparatus, means are provided to measure out a known amount of scrubbing liquid, means to draw or force a measured quantity of gas through the scrubbing liquid in a suitable vessel, and means for expelling the scrubbing liquid for periodic examination, such as conductivity measurements.  The complete cycle of operations may be carried out by a single rising and falling body of liquid which is denser than and immiscible with the scrubbing liquid.  According to the arrangement shown in Fig. 1 which may be used particularly for the determination of the oxides of sulphur in flue gases, a mercury pump 1 and tube 2 are used to produce a reciprocating motion of the mercury, water pressure forcing the mercury from pump 1 into the connected system until the mercury has been forced from inner tube 3 into tube 2 when the water pressure has free access to the drain 4 via tube 2 and allows the mercury in the connected system to return to pump 1 until the inner tube is sealed, when the drain is sealed and the cycle repeated.  A valve 22 is provided and designed to allow the mercury to rise rapidly in the connected system, and fall slowly. The reservoir 6 contains a mixture of sodium carbonate solution and hydrogen peroxide and the reservoir 7 a mixture of barium chloride solution and hydrochloric acid.  When the mercury level is low, the solution from reservoir 6 fills tube 8 and rises in tube 9 to a level determined by the end 10 of the atmospheric tube in the reservoir. Similarly the solution in reservoir 7 fills tube 11 and rises in tube 12.  Any liquid in absorption vessel 14 drains into vessel 15.  As the mercury rises, the contents of vessels 11 and 15 are forced into the mixing chamber 16 the acid delivered from tube 11 being arranged to just acidify the solution from tube 15 and the contents of tube 8 into the absorption vessel 14.  The gas in the lower bulb of the gas pipette 17 is driven out through vent 18 and, when this is sealed, through the water seal 20.  The levels are adjusted so that the mercury reaches its highest point at the mark 21 and then begins to fall, drawing the gas to be analysed through pipe 23, absorption vessel 14, which may be filled with glass beads, and water seal 24 into the gas pipette 17.  The mercury falls to mark 25, unsealing the branch pipe 18, and stopping the flow of gas through absorption vessel 14.  The volume of gas passed through the absorbent is the volume of the gas pipette 17 and its associated tubes between the marks 21 and 25.  As the mercury continues to fall, the contents of absorption vessel 14 drain into tube 15 ready to be pumped to the mixing chamber and the tube 8 is recharged with absorbent.  A lapse of time for this process to be completed is ensured by bulb 39 provided below the gas pipette 17, the level of this bulb being below that of tubes 8, 11 and 15 and above that to which the mercury rises in pump 1.  The cycle of operations is then repeated.  When the contents of tubes 15 and 11 are pumped to the mixing chamber 16, finely divided barium sulphate is formed, the chamber being provided to allow time for the development of the precipitate, and a stirrer is preferably provided.  At each cycle, the charge in the mixing chamber increases until it syphons over via tube 26 to the observation tube 27 where the amount of turbidity may be compared visually with a sliding turbidity wedge or may produce an indication or record by a photoelectric method, which may measure the decrease in transmitted light or the increase in scattered light.  The volume of liquid discharged to the observation tube 27 is larger than the volume of that tube, each fresh charge entirely replacing the liquid already in the tube.  To check the accuracy of the device, provision is made for filling the observation tube with a standard liquid.  The mixing chamber is provided at the bottom with a mercury valve 32--33 which is not connected to the main mercury system.  The mercury pump connection is extended to tube 30 which is supplied by a constant level reservoir 31.  The reciprocating motion of the mercury delivers the standard liquid, which may be distilled water, to the flushing chamber 29.  The frequency of interpolation of the check readings is governed by the size of tube 30 and height of the overflow 34 with respect to the syphon in chamber 29.  The chamber 29 is arranged to flush when the chamber 16 is about half full by arranging the valve 32--33 so that when chamber 16 is practically empty, the mercury level in tube 33 uncovers outlet 38.  In consequence, the level of liquid in chamber 29 cannot rise about the level of tube 34.  When chamber 16 is half-full, the mercury just seals the end of tube 38, the chamber 29 fills up and flushes.  Sulphur dioxide and other reducing gases may be determined using iodine as a reagent, residual iodine being determined; carbon monoxide may be determined using defibrinated blood or palladious chloride as the reagent; hydrogen sulphide by means of a lead salt or paraphenylene dimethyl diamine; ozone by means of potassium iodide; ammonia by Nessler's reagent; chlorine by orthotolidine.  Substances which rotate the plane of polarised light and of which the sulphates are insoluble may be used for the determination of sulphur oxides by observing the amount of light passed through a Nicol prism when the light passing through the observation tube has already been polarised.  The shape of the tubes 8, 11, and 15 may be varied to influence the rate of delivery of the liquid, for example an inverted pear-shape shown in Fig. 4 gives maximum velocity near the end of the delivery and a sharp cut-off to the supply from the reservoir.