Simple distillation is a distillation under normal pressure. When the distilled liquid of pure vapor liquid will pass to the condensed to a liquid. The temperature between the distillation pure liquid is constant all the time. (pic1) When distilled liquid mixed with different boiling points the temperature is not constant and increasing throughout the distillation due to the composition of the vapor distillation.(pic2) when distilled mixed liquid that are very different boiling points. (pic3) The temperature is maintained at the boiling point of the both liquid and the separation layer.