Al-Chemistry: the Canon's Yeoman's Poisonous Trade
--Meghan Milburn, May 1999The RC notes correctly mention that Hg and S combine to produce mercuric sulfide (HgS) or cinnabar (they spell sulfide with a "ph"wonder if its a misspelling or taken from older references). The Merck Index does not provide any warning about this compound (though I would certainly not consider it non-toxic given its elemental constituents). If youre looking for a "highly corrosive and poisonous" compound, mercuric sulfate (HgO4S) fits the bill quite nicely. Theres a "Poison!" warning in its description in Merck. Mercuric sulfate may also be more appropriate for our Canon because it is used to extract gold and silver from pyrites.
Mercuric sulfide occurs naturally as the mineral cinnabar (red) and is used as a pigment. Its one of the "dyes" alchemists used in their color purification of base elements (black-> red-> white). I also believe it was used as a pigment in the production of manuscripts (so in this case the ink may be mightier than the sword!).
Both mercuric compounds would be accessible, easy to produce, and, presumably, used by the Canon during the course of his research. The mercuric sulfate would be used to extract real gold and silver while mercuric sulfide actually was the "philosophers stone" for the dishonest Canon in the Yeomans story. This compound would color the reactant mixture red and, if the patron believed in the doctrine of alchemy, turn the base metal into precious metal.While researching alchemy for my presentation, the color scheme I found was black-> red -> white while the RC lists the transformation sequence as black-> white-> red during Chaucers time. I suppose its because there were various alchemical schools that had their roots in different theories (Egyptian, Arabic, Greek) that these discrepancies occur. But white seems a more appropriate final color because of both its religious significance and its implications of the "purity" of the final chemical product.