Studies on the electrochemical processes at the interface between two immiscible liquids began a long time ago: they date back to the end of the last century. Such celebrated scientists as Nemst and Haber, and also young A. N. Frumkin were among those who originated this science. Later A. N. Frumkin went a long way in furthering the studies at the Institute of Electrochemistry. The theory of the appearance of potential in a system of two immiscible electrolytes was developed and experimentally verified before the beginning of the thirties. In later years the studies in this area considerably...