The symbol is a dual-wielding Mercury. The text on the upper-left side of him reads ‘Per Sal, Sulphur, Mercurium Fit Lapis Philosophorum’ Philosophorum’ (The Philosopher’s Stone is Made Through Salt, Sulphur, and Mercury). On the upper-right: “Salt (🜔) Sulphur (🜍), and Mercury ( ☿ ), is the beginning of our life and of the life of all things.” The body of the text below discusses the ‘Dew of Heaven and the Fat of the Earth’, which is taken from Genesis 27:28: “Therefore may God give you of the dew of heaven, and of the fatness of the earth, and an abundance of grain and new wine…” The rest of the text concerns elaborate, enigmatic, physical and meta-physical explanations of the Philosopher’s Stone.  

The bottom concludes with the line “It is nothing else but the coagulated Blood of the Red Lion, and the Gluten of the White Eagle. If you discover it, be silent and keep it sacred. Trust to nobody but to God.” Earlier in the document there is a ‘glossary of occult terms’, which defines the White Eagle thusly: “The spiritual soul. ‘The Gluten of the White Eagle,’ – pure spiritual love, the fiery substance of the spiritual soul.” Gluten is defined simply as ‘adhesion; i.e., ‘of the spiritual substance. – see Eagle’.

I draw our attention to this image because the editor(s) were clearly familiar with and borrowed from many alchemical works from the Early Modern Period (c. 1450-1750), and in the case of this Mercury image, from the 12 Keys of Basil Valentine, a famous alchemical treatise originally printed in 1599.

Historians still aren’t certain who this Valentine character was, (his name likely a pseudonym), but the compilers of the Geheime Figuren clearly had access to his works in the 18th century and used, in this particular page, the ‘second key’. Earlier in the GF they featured the seventh key as well which shows a woman holding scales (Lady Justice) leaning over an alchemical apparatus with the names of the elements and the word ‘CHAOS’ surrounding them.