Rasarnava 4.25

4.25

gandhakasya kṣayo nāsti na rasasya kṣayo bhavet
kṣayo yantrasya vijñeyaḥ yantre vikriyate kriyā
alābhe kāntalohasya yantraṃ lohena kārayet //

There is no loss of sulfur, nor does loss of mercury occur;
the loss should be known to be of the apparatus, [for] the operation is wrought within the apparatus.
If loadstone is not obtained, one should have the apparatus made of iron.