Rasa Shastra: the chemistry of mercury

01The books of rasa

Rasa means mercury here, and the texts treat it as the seed of Shiva, to be purified before use. The Rasaratnakara is ascribed to a Nagarjuna, though which one and when is disputed. The Rasarnava, a Shaiva tantra of about the 12th century, and the Rasaratnasamuccaya of the 13th or 14th describe eighteen samskaras of mercury, the making of kajjali (black sulphide of mercury ground with sulphur), and the preparation of bhasmas, metal ashes, from gold, iron, copper and tin.

02Apparatus and zinc

These books describe the yantras of a working laboratory: the dola yantra for boiling a drug hung in liquid, the patana yantras for sublimation and distillation, the tiryak patana that sends vapour sideways into a cool vessel, and the koshthi furnaces with bellows. The Rasaratnasamuccaya describes getting a tin-like metal from rasaka, calamine, by heating it in a closed crucible turned downward, which matches the downward distillation of zinc found in excavation at Zawar. Acharya P. C. Ray gathered these texts in his History of Hindu Chemistry (1902, 1909).

03The safety debate

Rasa physicians hold that shodhana, the purifying steps, makes metal preparations safe, and traditional pharmacies still make them under Indian law. A 2004 study in JAMA found lead, mercury or arsenic in 14 of 70 Ayurvedic products bought in Boston, and cases of lead poisoning have been reported. Researchers in India are now testing how the classical processes change the metals’ chemistry. The fair statement is that the processing is real chemistry and that its safety in each preparation has to be shown by testing, not assumed.

In the texts

• Rasarnava
• Rasaratnasamuccaya
• Rasaratnakara