Patent GB-477849-A (GB)
Title: Improvements in methods and apparatus for measuring ion-concentration
IPC: G01N27/416
Filed: 1936-07-06
Abstract: 477,849. Potentiometers; determining physical qualities. KENT, Ltd., G. July 6, 1936, No. 18765. Convention date, Jan. 11. [Class 37] A system for the continuous measurement of the ion-concentration of solution flowing in a conduit comprises a cell for creating a potential dependent on the ion-concentration of liquid fed thereto and a source of calibrated potential with which the cell potential is compared, wherein means are provided for feeding solution from the conduit to the cell as a stream broken into drops to avoid the formation of an electrically conductive path from the cell through the stream. The ionconcentration cell comprises an insulating casing F of glass, phenol condensation product &c., in which a glass testing electrode GE and a calome 1 reference electrode RE are arranged. The liquid under examination which flows through a conduit GC, preferably earthed, is caused to drip through a vessel 14 into a pipe 15 leading to the first chamber of the cell F whence some flows into the second chamber of the cell and emerges in drops from a pipe 19, while the overflow of the first chamber drips from a pipe 17. The insulating casing F and the separation of the liquid into drops enable the electrode structure of the cell to be completely insulated from earth. The electrode GE is connected to the control electrode CE of a valve V, having a high input impedance and a low output impedance, and the electrode RE is connected to a contact P adjustable along a slidewire CS, which is connected in series with resistances R ... R<4> across a voltage source E. The output of the valve constitutes one arm of a Wheatstone bridge and the galvanometer or other measuring device GA is connected to an adjustable contact P<1> and to a second contact P<2> adjustable along a slidewire S, when the switch 3 is in its upper position as shown. When the switch 3 is depressed the galvanometer is connected in series with a standard cell SC across a resistance R<3>, and a resistance SR is adjusted until the voltage drop across resistance R<3> is equal to the voltage of the cell SC. The reading of the galvanometer GA is brought to zero when the control electrode CE is earthed, the switch 3 being in its upper and normal position, by adjusting the contact P<2>. The internal shield IS of the valve is preferably earthed and the resistance R<5> across the slidewire CS is earthed at its mid-point, or at its end when a silver, silver-chloride electrode is used. The ion-concentration in the cell. F is determined by adjusting the contact P along the slidewire CS until the galvanometer reading is zero, and the scale 9 may be calibrated in suitable units to give this value directly. Condensers K<1> K serve to byepass alternating currents in the leads to the electrodes CE, OE and the source of voltage E may be floated across a charging system having a voltage regulator VR. Continuous measurements may be made using recording mechanism having a mechanical relay which effects adjustment of the contact P in accordance with the deflections of the galvanometer GA. Automatic control of the ion-concentration may be effected in accordance with the deflections of the galvanometer.