The Green Lion, as it were, is a literal symbol of “Vitriol Of venus,” a green dense sulphuric liquid (acid) that the alchemist identified as being capable of dissolving most any mineral except gold. This ability to eliminate “dross” earned the substance high regard for its value in the retort, and regarded as a sacred, therefore “Royal” substance. Once discovered, the idea was adopted by most in exoteric alchemy as a breakthrough that had led them to the doorstep of the elixir vitae (elixir of life), and ultimately the Lapis Philosophorum (Philosophers Stone). If you look at the images of the lion ATTEMPTING to devour the sun, you will typically see an expression on the face of the sun that is in some way mocking the effort, usually as though Sol was growing annoyed or becoming irritated but there is no indication that the lion is going to succeed. Yes, the lion is likewise an archetypal symbol of the sun itself, so therein we are confronted by a paradox. – J.T Metts(Quora)

 ‘The Green Lion Devouring The Sun’ is a popular alchemical symbol. On a chemical level this is a metaphor for when a green, liquid sulfate called “vitriol” purifies matter, leaving behind the gold within the matter. Very pure vitriol is an acid that eats through practically anything, except gold. To naturalist alchemists, the Green Lyon metaphor described the process whereby plants used the rays of the sun to facilitate their own growth – a process we call photosynthesis.  On a human level, the green lion eating the sun is a metaphor for when a person’s “consciousness [is] overwhelmed by violent, frustrated desires” (Fabricus). In other words, inside a person, when the metaphor of the green lion eating the sun takes place, the person is compelled to act out destructively. In contrast, when the green lion eats the sun in a person on a higher spiritual path (for example, an alchemist), the person allows the green lion to eat them in order to be purified — to become spiritually golden. “There is this one green lion, which closes and opens the seven indissoluble seals of the seven metallic spirits which torments the bodies, until it has perfected them, by means of the artist’s long and resolute patience.” — “The Cosmopolite,” (16th century) – https://www.tumblr.com/ancienttimenews/147300973033/inthegnosis-green-lion-devouring-the-sun