For the equilibrium solid phases occurring in the systems: KCl−KBr−H2O, K2SO4−(NH4)2SO4−H2O and KNO3−NH4NO3−H2O, the concentration dependencies of differential solution enthalpies, ΔsolH2 for several crystallization paths, were measured. The limiting differential solution enthalpies, ΔsolH20
, were determined by extrapolation of the above dependencies to the ionic strength,Im0
, corresponding to the appropriate binary solutions. For KCl−KBr−H2O system only, the clear dependence between ΔsolH20
values was found and discussed.