Aqua Oleum is taken from an alchemical manuscript on the nature of the soul.

The manuscript also discusses the problems and difficulties of mixing wordly values with those born of Aqua permanens - unchanging water. An essential oil, being the essence of the plant, can be seen as a bridge between spirit and matter.  The main course of Alchemy was the union of these opposites on a psychological level.  Water is also used to extract most of the oils from their raw materials.