Calomel Classic Formulas — Natural Herb Library

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Attacks toxins and kills parasites - used externally for scabies, ringworm, chronic sores, and other stubborn parasitic or fungal skin conditions.
Relieves itching and dries Dampness - especially valued for intensely itchy, weeping, inflamed lesions where toxic Damp-Heat has lodged in the skin.
Removes putridity and promotes tissue regeneration - incorporated into chronic-ulcer ointments when decayed tissue must be cleared so healthy flesh can regrow.
Drastically purges retained water in rare internal use - historically used in tiny supervised doses for severe excess edema or ascites with bowel obstruction, but this is now largely of toxicological interest rather than routine practice.

Sheng Ji Yu Hong Gao (生肌玉红膏) - famous wound-healing ointment in which Qing Fen helps remove putrid tissue and promote new flesh in chronic ulcers.
Zhou Che Wan (舟车丸) - drastic hydragogue formula demonstrating the old internal use of Qing Fen for excess water accumulation and constipation.
Shen Jie San (神解散) - topical antiparasitic powder traditions combining Qing Fen with sulfur and other external agents for severe itching and skin infestation.

Me & Qi identifies Qing Fen as mercurous chloride and emphasizes that its principal role is external use for parasites, itching, toxic sores, and putrid ulcers.
The same source also preserves the historical internal use for severe edema while strongly framing it as toxic and tightly supervised.
MINERAL TOXICITY NOTE: unlike less soluble mercury sulfide medicines such as cinnabar, Qing Fen is a more hazardous common mercurial and should be treated as a high-risk toxic mineral product.