Application of compensated valve-voltmeter to measurements of glass electrode potentials
A. S. McFarlane · Journal of Scientific Instruments · 1933
Used in a null method of potential measurement, the valve-voltmeter described here has a maximum grid-input impedance of 5000 megohms, which is eminently suitable for recording glass electrode potentials. The voltage sensitivity is considerably greater than that of electrometer valve instruments as a class, and the instrument is more sensitive, and has a more stable zero than other instruments of a similar type using ordinary valves. Glass electrode potentials are measurable with it with an accuracy of 0.05 millivolt, which is roughly equivalent to 0.001 p H.