I much wonder that _Farnner_ was not afraid to offer this process to
others at a price, which is plainly and clearly described in many
places of my Books: and is done only by Nitre, by which sulphurous
metals (but not all metals and minerals, as he vainly boasteth) are
reduc’d to dross, from which by spirit of wine, a metallick tincture
may be extracted, as we have shewn above in the tract of the Alkahest:
that dross is truly fiery, and therefore easily attracts air, and is
turn’d into oil, of which I have largely treated in the second and
fourth parts of (_Furn._) and in the _mineral work_ especially in
the explication of the wonder of the world, as also in my Hermetic
Colloquies.