> pharmacist: that's not true - there are usually coloring
> agents, ketones and other more or less reactive stuff
> added as denaturants.
Not always. The stuff I can easily buy is colourless and contains only a small amount of denaturant. I don't know exactly what is used in the cheap OTC stuff, I assume some pet ether fraction, bitrex, MEK or IPA and traces of pyridine. I never bothered to clean it up and used it straight out of the bottle with good results.
If you order denatured EtOH from a chem supplier you can often decide which denaturant will be present. Fluka for example used to offer EtOH with all kinds of different and known denaturants. But compared to the €1.50 OTC stuff that EtOH is way overpriced.
> I have never been able to clean gas station ethanol into
> something usable for chemistry, not even by fractional
> distillation.
That's the whole point of denaturing, making it absolutely impossible (or at least too damn difficult and costly) to clean it up so that nobody will ever be able to drink it without getting seriously sick. Many have tried so far, but most if not all never succeeded. It's the state protecting its tax revenue. That's why clean EtOH is so expensive even though it's dirt cheap to produce it industrially.
I'm not fat just horizontally disproportionate.