Metals are all identical in their essence; they only differ by
their form. The form depends on accidental causes which the
artist must seek to discover. The accidents interfere with the
regular combinations of sulphur and mercury; for every metal
is a combination of these two substances. When pure sulphur
meets pure mercury, gold results sooner or later by the action
of nature. Species are immutable and cannot be transformed
from one into the other; but lead, copper, iron, silver, &c.,
are not species. They only appear to be from their diverse
forms.
ALBERTUS MAGNUS:--“De Alchemia.” (About 1250.)