Ros Gedeonis (Gideon’s dew) is a synonym for the aqua permanens, hence for Mercurius… the water I have spoken of is something that comes down from heaven, and the earth’s humidity absorbs it
Jung identifies dew as a central alchemical symbol equivalent to the aqua permanens and Mercurius, descending from heaven to purify and whiten the blackened prima materia.
, The Practice of Psychotherapy: Essays on the Psychology of the Transference and Other Subjects, 1954thesis