Is this how I do it?
Stock solution, 50% (by weight): Add 100 mL of distilled water to 100 g of reagent grade sodium hydroxide (NaOH) pellets and stir until solution is complete.
Yes. Except that you better
add the NaOH (slowly and in several steps) into the water, and not the other way round (
Don't trust everything in teh interwebz! Spills of boiling, concentrated lye, splashing around are no fun.). And 200 g solution is quite some wasted NaOH, except when you're planning to use it further on.
Sodium carbonate (one major decay product of lye with extended air contact) is easily soluble in water and dilute NaOH solution, but hardly soluble in concentrated lye. The old-fashioned way to get pure lye solution is to dissolve as much NaOH (of unkonwn purity) into water as possible (saturated lye). Possible Na₂CO₃ impurities first dissolve, but then precipitate the more NaOH dissolves and “grabs” the water off the carbonate to stay in solution. Then you can filtrate the (turbid) solution, and determine the concentration by titration,
density, or
temperature.
In inversion of this argument, the presence/absence of turbidity points to soda ash. On the other hand, the carbon dioxide bound in the soda ash should have appeared during titration already (fizzing) – but probably, the 6% solution that
@DeeAnna recommends (for good reasons: dilution = precision, and to keep heat of neutralisation under control) is just too dilute for visible bubbling to occur (CO₂ is reasonably soluble in water and dilute solutions).
What I'm wondering rn is what the 22% of your lye are, that aren't NaOH. It can't be mainly water, since then it'd be very sticky. Soda ash? Not sure, it would help to see bubbles, or crusty bits of white stuff floating in concentrated solution.
Point is, I don't know if someone has a definitive answer if sodium carbonate eventually (during months of cure) might or might not take part as an active base in saponification, i. e. if one has to count the carbonate as active (but slow) lye – or it's just some “ballast” in the soap (like glycerol, or salt in salt bars). Sodium carbonate gives a slightly positive result in the zap test. On the other hand, zappy soaps can lose their zap over time, when surplus hydroxide catches CO₂ from the air, to form (milder, but still irritant) carbonate.
My largest batch so far was from some 11 oz of oils. Guess I'm an impostor all the way down.
), but you have gained a bit more headroom with lye purity in question.
