Heterogeneous azeotropic distillation in packed columns is often very difficult because three phases, i.e., two liquid phases and one gas phase, can occur. In this type of distillation, also known as three-phase distillation, the second liquid phase can change the mass transfer efficiency of the packing in a significant way. The present paper focuses on simple distillation experiments with the mixture acetone/water/toluene. The evaluation of these experiments helps us better understand the effects of a second liquid phase on the mass transfer in a packed distillation column.