“And so that you cannot stray from the right path, apply yourself to metals; for the aforementioned sulfur is found in all” - Nicolas Flamel. Testament of Nicolas Flamel
“from these bodies there is extracted an exceedingly white and red sulphur; for in these there is a most pure substance of sulphur, cleansed to the highest degree by Nature's own artifice.” - Arnold de Villa Nova The Golden Tract Concerning The Stone of the Philosophers
“No external thing which is not derived from these two [sulphur and mercury] has power to produce or transmute metals. On this account we must select a metallic substance for the production of the Stone.” - Draco. The Golden Tract Concerning The Stone of the Philosophers
“The Sages have striven to discover how those sulphurs may be extracted from those more perfect bodies, and how their qualities may be so refined by Art, that that which was not manifest before (although it always lay hid in them) may appear by the mediation of the said Art with Nature. - Richard the Englishman, following Avicenna, affirms (cp. xi.). The Golden Tract Concerning The Stone of the Philosophers