As the title suggests, we introduce a novel differential approach to solution thermodynamics and use it for the study of aqueous solutions. We evaluate the quantities of higher order derivative than the normal thermodynamic functions. We allow these higher derivative data speak for themselves without resorting to any model system. We thus elucidate the molecular processes in solution, (referred to in this book "mixing scheme"), to the depth equal to, if not deeper, than that gained by spectroscopic and other methods. We show that there are three composition regions in aqueous solutions of...