https://doi.org/10.1351/goldbook.D01831
The equilibrium characterized by an unequal distribution of diffusible ions between two ionic solutions (one or both of the solutions may be gelled) separated by a
membrane
which is impermeable to at least one of the ionic species present, e.g. because they are too large to pass through the pores of the membrane
. The membrane
may be replaced by other kinds of restraint, such as gelation
, the field of gravity, etc., which prevent some ionic components from moving from one phase to the other, but allow other components to do so.