GB880428A - Improvements in or relating to titrimetric apparatus - Google Patents

Abstract

<PICT:0880428/III/1> In titrimetric apparatus comprising a bulk sample-taking device, a metering device and a titration vessel, a valve-controlled pneumatic system, the valves of which are operated by an electrical control system, is provided to operate in sequence the bulk sample-taking device and the metering device, and transfer the measured sample to the titration vessel. The invention is described in relation to a titration in which a liquid to be titrated (e.g., containing uranyl nitrate and free nitric acid) is treated with a conditioning agent (e.g., potassium oxalate to complex the uranium) which also serves for generation of titrant (potassium hydroxide) by electrolysis. The apparatus is particularly suitable for use with titrations of radioactive liquids, e.g., to determine the acidity of a liquid formed during the separation of plutonium from uranium and/or other fission products. As shown in Fig. 1, a liquid to be tested continuously flows through trough 3 and samples therefrom are taken as follows: initially valve 6 is closed and liquid flows through hole 2 into cylinder 1 to the level of the bottom of tube 7; valve 6 is opened to admit compressed air to the cylinder and some of the liquid is blown through tube 7 into catchpot 8 and the remainder is expelled into the trough; the valve is operated to repeat this cycle sufficiently frequently to fill the catchpot 8 between each titration. An overflow line 10 is provided. When the catchpot is filled, the electrical control system is manually brought into operation:-(1) to open valve 25 to air line 15 thereby ejecting liquid from pipette 18 into the catchpot and by bubbling air through the liquid, mixing the sample; (2) to close valve 25 and open valve 23 to allow liquid to re-enter pipette 18; (3) to close valve 23 and open valve 21 whereby liquid is forced through pipe 24 above T-junction 27 and along pipe 26 to electrodes 28, 29 operating a proximity switch which closes valve 21 and opens valves 25, 23 to eject a column of liquid of known length, i.e. from junction 27 to the electrodes, into titration vessel 30 and return the remainder to the catchpot; when the tube 26 has been dried by the current of air the proximity switch re-opens, closing valves 23, 25; this operation may be performed repeatedly to provide an adequate sample: (4) to open valve 54 to permit the conditioning liquid in bottle 56 to flow into the reaction vessel through line 61; (5) when sufficient liquid has been added, to switch on magnetic stirrer motor 42 and open valve 52 to clear the syphon tube 44 in preparation for titration; (6) to switch on current to an electrolytic cell 59 so as to generate titrant from the conditioning liquid in bottle 56 as described below simultaneously with a half second generator as timer; as the pH in vessel 30 varies, pH electrodes 34, 35 return a signal to an amplifier and thence through a derivative network to a discriminator which switches off the current to cell 59 and the timer at the end point; the quantity of titrant may be calculated from the current in the electrolytic cell and the time taken; the derivative network provides means, determined by the rate of change of pH, to operate the discriminator prior to the true end point in such a way as to compensate for titrant formed but still remaining in line 61 when current is cut off from the cell; (7) to close valves 52, 54 and open valve 50 to connect water line 39 to vessel 46 and thereby begin a syphon action resulting in the emptying of titration vessel 30; (8) to close valve 50 and open valve 40 to wash the vessel and permit the pH electrodes to remain in water when not in use; (9) to close valve 40 and open valve 16 whereby the Venturi 17 creates a partial vacuum in vessel 12 having outlets 13 and syphon line 11 to return liquid in catchpot 8 to the trough. Operation (7) is repeated to empty the water from vessel 30 before a second titration is performed. An overflow vessel 32 is provided to enable any scum formed in vessel 30 to be washed upwardly out of the vessel. Where separate conditioning and titrating liquids are to be employed, an additional bottle is provided. An alternative method of obtaining a larger sample for the vessel 30 is described in which tube 7 has an outlet jet which leads into a measuring vessel having an upper vent and compressed air line and a lower syphon leading to the titration vessel: when the liquid level in the vessel reaches the jet, further liquid is returned to the cylinder 1, and by ceasing to supply the liquid to the measuring vessel and applying pressure, the sample is forced into the titration vessel. By dividing the flow of conditioning liquid from vessel 57 into lines 60 and 61, which contain respectively an anode 62 and a cathode 63, the titrant is generated in line 61.