Precipitation Membranes. I. The “Conditioned” state

Membranes which are generated from two ions of opposite charges by diffusion-controlled precipitation and which can act as selective ion barriers, are called “Precipitation Membranes.” The “conditioned state” of the membrane is responsible for the barrier effect. A prerequisite for the existence of this state is that certain minimum concentrations of the two ions, from which the precipitate is formed, be present in the adjoining solutions. The ion barrier is an electrical barrier formed by a positive and a negative equipotential plane within the membrane which are caused by adsorbed surplus ions on two precipitate layers. Conditioning experiments are carried out with BaSO4-cellophane membranes, the system studied particularly in this and the preceding papers. By studying the time evolution of the membrane potential, one gains insight into the process of “conditioning.” A rather sudden rise of the curve indicates the spontaneous creation of the ion barrier. Obviously, this event is a cooperative phenomenon of a statistical character. The counter diffusion of the two reagents involved plays an essential role