Here's something I read on usenet lately:
"Hi,
I'm going to be doing an extraction soon and I was wondering something.
My local shop doesn't sell rock salt, which is what I normally use; I live in quite a remote area so I won't be able to get rock salt until I next go to the Big City to marvel at the clockwork radios and get some wick for my lanterns.
The shop here does sell lo-salt, which it says is 60% potassium chloride, 40% sodium chloride (or something close to that). No anti-caking agent like normal table salt. Will this do the same job?
If you can answer this question, explaining why or why not would make it immeasurably more useful.
The last few extractions I've done, I add rock salt to my water before the lye as a matter of course. I can then mechanically stir the solvent (very vigorously, for a full 10 minutes) into the base with an electric drill and plaster paddle. It separates fine.
A bucket or tub with a tight-fitting lid and a hole just big enough for the plaster paddle works well for this.
FWIW I think that's the way to go; you have a real sense that you aren't leaving anything behind in your basic solution.
I also found a mixture of Sodium Hydroxide and Sodium Carbonate around here somewhere; would that be strong enough as a base? The pack doesn't list the proportions.
Thanks."