Patent GB-282170-A (GB)
Title: Improvements in means for effecting the chemical analysis of liquids and controlling chemical operations
IPC: G01N27/02
Filed: 1926-09-20
Abstract: 282,170. Hatfield, H. S. Sept. 20, 1926. Mixing fluids in flow.-Apparatus for indicating the proportionate amount of a constituent in a liquid, applicable to the control of a water-softening plant, is arranged to record automatically any alteration in electrical conductivity of the liquid due to chemical change, dissociation, or elimination of the constituent in question. Fig. 1 shows an apparatus for automatically measuring the temporary hardness of water. The water to be tested is supplied through a pipe 1 to a pipe 2 coiled to form a fash boiler 4 where the water is evaporated to dryness, the solid residue constituting both the permanent and temporary hardness being shot forward with the steam. The steam is condensed in the coil 6 of a condenser 7, the solid residue constituting the permanent hardness being redissolved. The part forming the temporary hardness is caught by a gauze filter 6<a> and is periodically removed. Two identical cells 11, 12 are provided each consisting of a pair of electrodes 15, 16 and 17, 18 spaced apart by ebonite or other insulating tubes 19. The cell 11 is supplied through a pipe 13 with untreated water, and the cell 12 is supplied with the water from which the temporary hardness has been removed. The cells 11, 12, in series with resistances 25, 26 are arranged to form two arms of a Wheatstone bridge, of which the other two arms are formed by equal resistances 22, 23. Alternating current is supplied from mains 24, an alternating-current relay 27 being connected in the cross-connection of the bridge. Balancing of the bridge is effected by moving a contact arm 28 over the resistance 26, which consists of a coil of thin wire wound on a cylinder 31 fastened in a sloping position on a vertically-movable frame 32. This frame is suspended by a chain 34 from the end of a lever 35 which is moved by the expansion or contraction of a zinc rod 37 arranged in a long tube 38 to which water is admitted from the pipe 1. Variation in temperature of the water under test is thus compensated for. Unbalance of the bridge causes the relay 27 to close one of two contacts 41, 54. Assuming the contact 41 to be closed, a circuit including a battery 42, a contact 43, and an electromagnet 44 is closed. The contact 43 is arranged to be closed intermittently, so that the electromagnet 44 intermittently attracts its armature 45, which carries a pawl 46 and drives a ratchet-wheel 47. This drives a toothed wheel 48 carrying a friction roller 57, between which and a second friction roller 58 a rod 49 is gripped. The lever 50 carrying the contact arm 28 is thereby moved until the bridge is balanced, when the contact 41 is broken. Should the contact 54 be closed, an electromagnet 55 is energized and attracts its armature 56 carrying the roller 58, thereby releasing the rod 49 and allowing the lever 50 and arm 28 to return to their zero position. The arm 50 is extended beyond the pivot 51 and carries a pen 52, which makes a record on a chart 53. This mechanism may be applied to the control of water-softening plant in place of that shown in Specification 282,168, in which case the contact 43 may be intermittently closed by means of the tipper shaft. Fig. 2 shows a cell for use when the current causing a chemical change in one of the constituents of the liquid flowing through the cell is also used to measure the change in that constituent. An elongated chamber 60 is formed with a flat porous tap 61, which is ground flat and carries a lead or other electrode 63 formed with a zig-zag channel 64 through which liquid flows from a pipe 65 to a pipe 66. A second electrode 67 is contained within the chamber 60. Normally, if the electrode 63 were used to reduce a constituent of the liquid, for example to combine hydrogen with chlorine or chloramine, the electrode 67 would effect a corresponding oxidation. The liquid, however, percolates through the porous top 61 by gravity, but the products formed at the electrode 67 are prevented from passing back through the porous top 61 and mixing with the stream of liquid flowing through the channel 64. In the apparatus shown in Fig. 2 of Specification 264.237, the mixture of the two liquids may be made automatically, and the resistance of the mixture recorded, whereupon the reaction vessel is emptied and a fresh charge introduced. The flash boiler 4 may be replaced by an ordinary boiler, and the gas burner 5 may be replaced by an electric resistance.