Three systems, isobutyric acid - water (I-W), "(I-W) + 5 10(-4) M (KCl)" and "(I-W) + 5 10(-3) M ( KCl)", have been studied by measuring the electrical conductivity sigma (Omega(-1)cm(-1)) along the coexistence curve in a single phase, as a function of the variations temperature T and composition X in acid. The coefficient s is a temperature dependent parameter for ions, increasing as temperature is elevated. Contrary to the visconty, the electrical conductivity does not show any anomaly in the critical region.