Anandakanda 1.7.64

1.7.64

amlena mardayed gāḍhaṃ pacet tadbhūdhare puṭe /
evaṃ ṣoḍaśaparyantaṃ rasaṃ pratipuṭaṃ kṣipet //

grind thoroughly with sour gruel, and cook it in a subterranean pit kiln.
In this manner, one should add mercury at each roasting, up to sixteen times.