Saturday, December 22, 2012

Potash 1

I was on the verge of just buying some firewood and burning it in a convenient fireplace (rather a waste because it's summer, and quite warm) when I was struck by an idea: I wonder if that wood-fired pizza place down the street does anything with their ash? Indeed they did not, and while I did get a strange look or two, I walked out with about 35lbs of ash and charcoal ends.
  • I filled a big stainless steel (not aluminum!) pot with 8lb of the mixture (about 1/3 full)
  • I topped it to 2/3 with water.
  • I stirred it thoroughly with a wooden spoon
  • Immediately large chunks of charcoal floated to the surface, and I picked them out and discarded them
  • I left the rest to sit for a while, coming back to stir it occasionally
  • After an hour, the top was covered with small unburnt wood & charcoal, which I strained off and discarded.
  • I used a ladle to dip out the clear fluid from the top of the container
  • I added more water, stirred, and repeated the process after another hour.
  • After 2 more repeats of the process, I had about 2L of potash solution
  • I discarded the wet ash
  • I put the liquid in some glass oven trays and dried it
The potash liquor (direct from the ash) is a honey-to-dark-brown color, and the potash is light brown (more like sand than salt).

Since potassium carbonate and sodium carbonate are both white crystals, I assume the brown stuff is some sort of impurity. I tried dissolving the potash in alcohol, to no avail. Neither the potash nor the brown component dissolved in it. Other people seem to have had the same problem:

at Caveman Chemistry
at Alchemy Forums

Some agricultural forums talk about "red" potash, containing iron impurities. Ferric sulfate has a sort of pinkish-brown color, but is "negligibly soluble" in water. Ferric nitrate is a very light pink. Iron carbonate is exactly the right brown color, but is totally insoluble in water (as are most carbonates). Ferric chloride has a variety of interesting characteristics (it's yellow, or green, or pinkish-purple) and it's soluble in water. So the mystery continues.

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