In solution, solute molecules B are coupled by attractive forces between them and all other molecules present; and these other molecules enhance the tension in the coupling force between solute molecules an amount πB, the osmotic pressure of the solution solute. Two equilibria determine thenoBmoles of pure solute which dissolve inn10Amoles of pure liquid solvent. If atTthe solute is solid and in excess, then 1) thenBlsatmoles of B in thenlAmoles of A in a solution saturated with B are in thermodynamic equilibrium with the solid solute at the sameTandpand 2) thenBlsatmoles of B andnlAmoles of A may also be in chemical equilibrium with the moles of new molecular or ionic species formed in the solution. Solute molecules dissolve until the chemical potential of the solution solute, plB(Tp, xBlsat), equals the chemical potential of pure solid solute at the sameTandp, μBso(T,p). When the solution is saturated with B and the mole fraction of B is xBlsat=nBlsat/σjn1j, then the vapor pressures of the solid solute atTandp, the solution solute atTandp, and the pure undercooled liquid solute atTandp-πBlsatare identical. If atTthenBlomoles of pure solute and thenlAmoles of pure solvent are liquids, then if molecules of B are allowed to dissolve in A while molecules of A are dissolved in B, the resulting solutions may 1) contain only molecules of A and B or 2) contain A and B which also react to form other ionic and molecular species. The two solutions may be identical or they may differ. In all cases, however, the mole ratio ofnlBnlAin both solutions must be identical.