The lion symbolizes gold or the sun. The Green Lion swalling the sun is an alchemical symbol for gold being dissolved in a mixture of nitric and hydrochloric acids called ‘aqua regia’ (royal water).
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In alchemy, the green lion eats the sun. 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.
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.