Hi rr, I've fooled with these myself and can share what I've done so far. Technical grade flake KOH is often available from custom (hobby) leather-hide tanning equipment suppliers. I'm pretty sure this is pure enough for the job, check it out for your self if you have doubts. I got mine from braintan in southern Oregon but you could find a closer 'hobby' supplier.
The article was in Homepower # 15 and you can download the issue from their website for a few bucks. The electrolyte concentration is listed in the homepower article; I'd give you a table from Utility Free, but right now my paperwork is totally scrambled, I'll try to get it to you later.
You can use a typical battery hydrometer, the kind with a scale, to measure your solution's concentration, but you will be urged by all concerned to go get a BRAND NEW ONE! They are pretty cheap from the local auto parts store, it's hardly worth it to poison your electrolyte or risk having the thing blow up in your hand. There's a way to calibrate your new hydrometer by making a saturated solution of salt - plain ol' sodium chloride, but no "iodized" or alumina for "easy pour" additives. Basically a saturated sodium chloride solution varies very little in specific gravity over a 5 degree celsius range, < 0.001. Again I'll have to resurrect my paperwork to give the details, and you'll have to very thoroughly dismantle and rinse the hydrometer after this procedure.
LiOH is getting expensive but can be found on the web, I got mine from Kyantec, good folks, Hazmat shipping on all these chemicals, BTW. And that brings up the points of safety and disposal. When you are mixing these things up into your distilled water, wear protective clothing like you had to in chem lab and for Pete's sake wear safety glasses, a respirator and do your mixing outside with the wind blowing any fumes away from you; the LiOH is particularly nasty. Wear nitrile gloves or go without fingerprints for a while. I kept a gallon of vinegar and another of lemon juice right there so I could take a sour shower if I needed to. This stuff is mean and it keeps on eatin'.
When I dumped my old cells, I made a rack that would hold them in place while I sloshed them back and forth to loosen the mud on the bottom, then tipped them upside down and drained the stuff into a plastic barrel, rinsed them with distilled and dumped that into the same, let it settle, then after a few weeks decanted the clear fluid off the solids. This is pretty much straight KOH in solution, and if you can test it you can titrate it with plain old sulfuric acid - lead-acid battery acid - and make potassium sulfate, a common fertilizer; the rest of the stuff, the mud, is definitely evil, and you'll have to talk to the hazardous waste people of your area about that.
What you do though is entirely up to your own good judgement so you will have to figure out for yourself what is prudent and lawful. Take care,
