A VACUUM TUBE POTENTIOMETER FOR RAPID E.M.F. MEASUREMENTS¹

Glass and other electrodes for measuring pH values of very dilute buffers and of distilled water

“…The isohydric indicator technic (1) is apparently applicable within 0.1 pH to such solutions and distilled water, but has not heretofore been compared with a reliable e. m. f. method. By adding Varley shunts to a modification of the vacuum tube potentiometer used by Partridge (5), keeping the grid attached to the circuit when balancing it, and using a Thomp-,son (2, 3, 4, 7) glass electrode, e. m. f. readings can be made within 0.1 to 2.0 millivolts on weakly buffered solutions and distilled water, and the pH values agree with those obtained by the isohydric indicator method. This combination is also suitable for measuring the pH of solutions containing active oxidizing or reducing agents, such as chlorine or tannins (6,8) where the hydrogen and quinhydrone electrodes and indicator methods might fail.…”

The Early Development of Electronic pH Meters

“…The papers that followed up on Goode’s pH meters fell into two broad categories: those that embraced its continuous-reading aspect and described improvements by using newly available tubes and/or alternative circuits − , and those that merely incorporated one or more vacuum tubes with a milliammeter instead of the usual null detector (until then: a more sensitive galvanometer, a capillary electrometer, or a four-quadrant electrometer) in otherwise traditional potentiometer designs ,− . For example, Treadwell reported that he had reproduced Goode’s results with a vacuum triode of different manufacture, and had likewise obtained a wide range of grid voltages for which the output voltage was, to within 1%, a linear function of the grid potential.…”

“…The first papers to apply Goode’s direct-reading approach − offered improvements and extended the method to other types of potentiometric titrations. In those early days, there were problems with the stability of the output voltages of the batteries supplying the rather large filament currents and filament-to-plate voltages then needed in vacuum tubes to generate and drive vacuum electrons, a problem that, some four decades later, was much reduced by the considerably smaller source-to-collector currents in, say, Metal-Oxide-Semiconductor Field-Effect Transistors (MOS-FETs).…”

Potentiometric Titrations

“…It is not necessary to plot the reading in many instances. A number of applications of the simple circuit have been described, and many other circuits have been devised (35,15,217,94,170,54,126,220).…”