> Piglia vitriolo Romano on iiij salnitrio on iij limatura achi > on. 1. et destilla alanbicco et piglia della prima aqua on 1/2 et po- > nili in essa 3 on de canfora et con questa fregate la faccia
> Take 4 parts [vitriolo Romano], 3 parts saltpetre, and 1 part > (iron?) filings, distill in an alembic, take half the resulting > liquid, mix (?) it with 3 parts camphor, then rub it onto the face.
I second your guess "on." = "oncia" (ounce).
I can't figure out "achi"; could it be a typo?