Glass Electrodes and Apparatus for Direct Recording of pH in Vivo *

FIG. 1. The wiring diagram of the microvoltmeter as it is used in pH measurements. The variable resistors should be of highest quality, and may be obtained from the General Radio Co. The tube bases should be removed and the cups at the bottoms of the tubes should be filled with paraffin. Special care should be taken in the construction of the switch in the grid lead of the sensitive tube as it must be of the anticapacity type and have very good insulation. The tubes are run much below the rated capacity, since a three-volt drop in the filaments is sufficient to insure satisfactory operation.