Clean up "Liquid Fire"

Currently it's the only source of sulfuric acid I have, so I'm fairly apt to use it. If you've never seen it, it's sold as a drain cleaner (incidentally, besides my source for hydroxides), and is a brownish liquid with a rank smell.

It's the brown I'm not liking here, if I react something with the acid (that consumes it) it appears as a sticky, tar-like substance on the walls of the vessel. It comes off with scour and some added soap, and appears to not affect what I've been doing, so far, which happens to be testing it -- it might be more inert than I think.

Any ideas as to what I could use to remove this? I'm fairly blank.

[Edited on 17-1-2010 by R0b0t1]

Obviously, distill it. Oh, and use heavy glassware...

If you're not feeling so adventurous, you might try heating it not as much with a small amount of oxidizer (permanganate and peroxide come to mind). I would limit the amount of oxidizer (i.e., make a solution and add slowly), since such mixtures are well known to run away and do much worse things than you're already trying to do. That means adding water to acid, and if that ever sounds like a better alternative, you know you're doing something dangerous.

Even hot sulfuric is a moderate oxidizer (e.g., copper metal is oxidized in boiling sulfuric acid, much as in room temperature nitric -- the result is SO2 gas instead of NO2). It may work just boiling it, with the bonus of increasing the concentration somewhat (H2O evaporates preferentially). The downside is, phenolic compounds may be sulfonated rather than destroyed, so it won't be as pure.

We've had plenty of threads on the subject, give it a search.

Tim