Disposition of two immiscible liquids

Two liquids arrange themselves so that their interface is horizontal, because only in this way is Stevino's principle satisfied. Several non-miscible liquids placed in the same container are arranged from top to bottom with a specific weight increasing with depth. This is because the tendency of the system is to bring itself into a condition of stable equilibrium. A distribution in which liquids with a lower specific weight are arranged lower than those with a higher specific weight would give rise to an unstable equilibrium configuration. For further details, see the book by Mossa and Petrillo, Idraulica, CEA, Milan, 2013 (page 114).
Contribution by Yolande Montanaro (Environmental Hydraulics course; A.Y. 2021-2022).