Purification (shodhana) of mercury

Mercury is ground well in a stone mortar with brick powder and milk (the verse: milk from the breast) and washed with kanji, which purifies it. The purified mercury is mixed with dry ginger, black pepper, long pepper, kanji, the salt group and asafoetida, tied in a bundle and cooked (steamed) through a dolayantra in a large vessel filled with kanji, over an unbroken fire, for three days, then washed with lukewarm kanji. The text says the mercury then becomes very pure and, like a demon, eats and digests all metals; the commentary adds that gold and other metals put into it mix at once, its weight does not increase, and they cannot be separated from it again.