Potash has been an important item of commerce for centuries. Until recently, its use was restricted to the manufacture of soap, glass, and black gunpowder. The salt was obtained by leaching ashes of wood and other vegetative wastes tn large iron pots-hence, the name "potash," It became the principal product of the chemical Industries in America before 1850 as a byproduct of clearing the virgin forest lands for agriculture. The total annual supply for these chemical uses, however, never amounted to more than a few thousand tons for the entire world. (p.123)As far as the production is concerned, the American Academy of Sciences ran a short article in 1793 that may be relevant to this, Aaron Dexter, Observations on the Manufacture of Pot Ash [sic!], in: Memoirs of the American Academy of Arts and Sciences, Vol. 2, No. 1 (1793), pp. 165-170.
First of all, the book repeats the information given by Mark L. Staker in his Whitney in Ohio article for BYU Studies 42.1 (2003), pp.75ff. So this makes it likely that when Staker speaks about "manuals", he had something this information in mind.
Dexter argues that quality of the potash needs to be improved (p.165) and that this low quality is not the fault of either the equipment or the impurities (p.166), but rather of the technique.
Too often, not all of the salts are extracted from the ashes.
For this purpose, rain or river water ought always to be preferred. The ashes should be saturated, and remain with about an inch of water over the top of them for twelve hours at least. (p.166)By straining the leach out of the tub, either with a small hole or a false bottom, so that none of the ashes can escape, water can be continuously replenished. The lies needs to be boiled
... until they are so reduced in strength, as they will no longer pay the expense of boiling. The ashes however, still to be preserved; and fresh water applied as before. And when drawn off, they may be used with profit on fresh ashes, as long as there remain in the lies any salts, which may be discovered by the taste. (p.166-167)Next, Dexter recommends double-filtering the lie, as it exits the tub and as it enters the receiver. Then it needs to sit for 24 hours. When transferred into the kettle, the sediment needs to be left behind in the receiver (p.167).
Every precaution should be taken to let nothing fall into the lies previous to, and whilst boiling. Therefore, that injurious practice of laying wood on the kettles for drying must be avoided. (p.167)[[RCK: it is hard to believe that putting wood on the kettles did dry them instead of steaming them.]]
The first drawn lie should be boiled down to half; later lies even more so. At that point, lime can be added, though mixing the lie into the ashes is fine too.
The lie should now cool off to the point that it is body temperature ("to the state of blood heat" (p.167)), and again there will be sedimentation, a "chalky earth", which needs to be detained. Once the earthy matters and the common salt (p.168) have been removed, using the same process as salpeter production uses for the common salt, the lie is ready to be fluxed. This involves boiling the lie down completely (p.168). Then the fire is increased to "for the purpose of destroying the inflammable substance" (p.169). Dexter provides a sliver-based test for evaluating the quality of the potash, which is re-dissolved in water and then a silver coin turned dark or black with it if the "inflammable substance" has not been removed. If the potash contains the "inflammable substance", then either re-dissolving in pure water and re-fluxing is required; or the potash is turned into "pearl ashes ... by calcination" (p.169).
Dexter knows that the process is discouragingly long, believes that the cleaned lie not only fluxes faster, but that the superior quality of the potash with fetch a better price (pp.169-170).
Dexter closes with the observation (p.170), that the importance of the subject matter, since potash production is even discussed by legislatures, and the need to be comprehensible to the business people and workers who produce the chemical, have led him to write the article in the straight-forward language chosen. (As an example, on (p.169), Dexter uses the term "oily substance" as an analogon for his "inflammable substance", because that is the term the workers use.)