Answer

The spirit has a low boiling point. This is the result of low forces of attraction within it's molecules. Due to it's low boiling point the spirit will start to evaporate at room temperature. Thus it appears as though the spirit disappears. So the phenomena responsible for the disappearance of spirit is evaporation. However, evaporation not only occurs on liquids with low boiling points it takes place at any given temperature, because the molecules of the liquid are in constant motion as will be explained in the video.