So i have a farm and we burn quite a bit of fire wood. I was wondering how to measure the concentration of the potash if i made it. I understand the boiling down of it to concentrate it, but how do you plug it into a recipe?
Being a bit of a prepper at heart, I was interested in this process - until I started reading up on it. All the floating egg/potato nonsense! Why can't any of those things just give a specific gravity? I've got hydrometers!
Most of the write ups on this method are from the old days or based on old methods -- I don't see too many science-y types getting into making lye from wood ashes. (Have you noticed it's almost always guys who have never made soap or are newish soapers who ask these questions about making wood ash lye, and when they don't get a quick, straightforward answer, they generally disappear? I'm not saying this to be snarky -- just a trend I've seen.)
Anyways, most rural/backwoods/pioneer types didn't carry hydrometers, but they did have chicken feathers and eggs. I have a letter written in 1742 from a soap maker who did use a hydrometer of the day to measure the strength of his lye, but he noted that he was the exception to the rule. He was using slaked lime to convert the carbonate lye into a hydroxide lye, separating the clean liquid from the residue by filtering, evaporating the liquid to concentrate the lye, and then measuring the density.
"...An hydrostatical Balance, a Water-poise, and other Instruments, might also give this Degree [of concentration]; but in the Country they are not at hand, and I judged it best to point out only what is most easy. Soapboilers use for this End a fresh Egg; if one half of it sinks into the Lye, they judge the latter to be of the first Strength, that is to say, that this is the Lye which they ought to employ last of all in their Manufacture; if the Egg sinks in to Two-thirds, the Lye is called the Second; and, lastly, if the Lye covers the whole Surface of the Egg, it will be called the First, and will be that with which they begin their Operation or Boiling. But this way of trying has not all the Exactness which can be desired, because all Hens Eggs have not the same specific Gravity...."