V.I.T.R.I.O.L.
A famous alchemical acrostic of seven words forming the Latin sentence:
"Visita Interiora Terra Rectificando Invenies Occultum Lapidem"
Which (Adam McLean)translates into English as:
"Visit the interior of the earth, in purifying you discover the hidden stone".
The word vitriol was chosen for this 'task' because of its caustic nature, for how else can one penetrate the hardness of stone?
For details on this process see tabula smaragdina hermetis.