Electrodes for the measurement of small bioelectric potentials.

Abstract

In connection with studies on certain types of small constant bioelectric potentials (about 0.5 millevolt) it has been impossible to use any of the electrodes in common use in physiological work.

The common Zn-ZnSO₄ non-polarizable type cannot be duplicated and marked variation in the E. M. F. with time occurs also. It was found that the E. M. F. of the more stable calomel electrode was susceptible to light and could not under the working conditions be maintained within a variation of 0.2 millevolt.

Cadmium amalgam CaSO₄ electrodes (saturated type of half Weston element) have not yielded the expected constancy under working conditions. The most stable electrode which has been tried so far, has been one made up with a three per cent pure lead amalgam and PbCl₂ in 0.05 to 0.01 molecular. The copper leads are dipped into copper amalgam instead of mercury. The drift in potential with time and at constant temperature was found to be sufficiently slow, and small enough to permit measurements of 1.0 to 0.05 millevolts with an error of about 0.01 millevolt under good conditions of experiment.