Anandakanda 1.23.122

1.23.122

divārātraṃ karīṣāgnau pacedbhasma bhavedrasaḥ /
<ekonatriṃśaḥ prakāraḥ>
mukhīkṛtarasaṃ cābhrasatvaṃ svarṇaṃ trayaṃ samam //

or cook it day and night in a cow-dung fire; the mercury will become ash.
<Twenty-ninth method>
Mercury with an open mouth, mica essence, and gold—these three are equal.