Electrical conductivity and viscosity of supercritical isobutyric acid + water solutions

The electrical conductivity of the isobutyric acid 4- water critical system has been measured for several concentrations including the critical. Measurements were made using a hybrid conductance/viscosity cell-a modified Ubbelhode viscometer-which permitted almost simultaneous measurements of viscosity and conductance. Absence of a conductivity anomaly was verified for T -T_c ≥ 0.03°C. The results of additional measurements made on a critical solution in which 2% of the protons were replaced by K⁺ ions clearly show that the absence of an anomaly is not simply due to the fact that, in this binary system, most of the current is carried by the proton. The possibility of an anomaly in the ac conductance quite unrelated to the viscosity anomaly and strongly dependent on bridge frequency, occurring (for audio frequencies) at smaller T -T_c values than those reached in this work, is discussed.