The Rasaratnākara — 'the jewel-mine of rasa' — is a treatise with a strong opinion: mercury is the king of medicines. Attributed to the Siddha Nityanātha, it opens with invocations to Gaṇeśa, Sarasvatī, and Haṭakeśvara, and then makes its case in a handful of verses.
Why rasa outranks everything
The argument is practical, not mystical: mercury works quickly, in small doses, and restores health fast.
Due to minimal usage and lack of interest in it, because of quick restoration of health, rasa (mercury/medicinal essence) is superior to other medicines. Rasa-vaidya (mercury/alchemical medicine) is not like ordinary vaidya (physician), it is divine, not human.
The same page invokes the lineage of alchemical medicine — Śiva's Rasa-khaṇḍa, Nāgārjuna, Carpaṭa-siddha, Vāgbhaṭa, Caraka, Suśruta — placing mercury therapy at the summit of a long tradition.
The purification of mercury
Mercury, the text insists, is not used raw. It has defects (doṣas) — sluggishness, dullness, lead- and tin-contamination — and the treatise's first duty is to describe how to remove them.
The purification of mercury (rasaśodhana) is described as easily accomplished with confidence, using mercury, sulfur, metals, oils, ghee, and poisons. For the benefit of physicians and yantra-users, for the welfare of the diseased, for the bodily perfection of the elderly, and for the curiosity of disputants — this five-sectioned treatise is dear and beneficial to practitioners.
Then come the procedures: washing in sour gruel, grinding with plant juices, sealing in crucibles, cooking over regulated fire until the mercury is 'killed' — reduced to a stable ash that can be dosed.
A medicine of the impossible
The Rasaratnākara is part of a tradition that aimed at nothing less than transmuting poison into medicine and metal into ash that heals. Its confidence — that mercury, properly handled, could treat what ordinary medicine could not — drove centuries of experimentation in the crucible. Reading it, you see the ambition behind rasaśāstra: to turn the most dangerous substances of the earth into the most useful.