[SquipSquop]

     I need potassium hydroxide for mycological reasons. It will be useful both as a contrasting dye for microscopy and as a chemical test to help identify various species of fungi. I think that synthesizing KOH instead of buying it will be a wonderful learning experience.

     My plan is to use a metathesis reaction of potassium carbonate and calcium hydroxide. I am under the impression that K₂CO₃ is a fair portion of wood ash and is water soluble. My plan to obtain K₂CO₃ is to mix wood ash with water, then filter everything that doesn't dissolve. I have yet to actually do that however, as I planned to obtain Ca(OH)₂ first and that is proving difficult.

     To obtain Ca(OH)₂ my plan was to heat ground seashells to at least 825° Celsius, which I believe contain calcium carbonate, yielding calcium oxide that I might then slake in water to get Ca(OH)₂. Sounded pretty good on paper, but I'm having a bit of trouble with the execution.

     So, to grind the seashells I used two steel spoons and a massive accomplice. So far so good, I can get just over 3 grams of a decent powder with a lot of very fine dust and some larger shards (none larger than 2mm in diameter). I could crush more finely with more work if needed. I then heated the powder from below for 10 minutes in the steel spoon with a propane torch. I then poured the spoonful of powder into a bowl of water. To my chagrin, none of the powder dissolved, and no measurable mass was lost to carbon dioxide during heating.

     I've tried and retried this process a few times, with similar results and so I've come here. I've tried heating from above and below using another spoon on top, and I heated the spoon as hot as I dared without melting it. I was originally only heating until the spoon had been glowing red orange for a few minutes, but extended the time when I learned of calcium carbonate's relatively high heat capacity. I've put in a fair amount of work trying to figure this one out, but frustration has driven me to create an account and post here in the hope that someone with some greater insight will tell me what I'm doing wrong.

     Thank you, any help is greatly appreciated be it with my calcium based conundrum or the other parts of my plan I have given.

[Arkcon]

Ok, there's lots here in the wall o text.  I'm on M hone, and I'll do what I can.

Ahem.

You should buy KOH.  There, that's over with.  Now, back to work for me, here at the chemical forums.

Please write out your metathesis reaction, and be ready to try to under stand it.  If the reactants aren't water soluble, the reaction will be slow.  If all products ducts are soluble,then you will not isolate much of the desired product.  Investigate this critically, and abandon this project is this is the case.

[Arkcon]

We have another thread about roasting sea shells.  Calcium carbonate is a refractory material,we use it to make furnaces, because it is very resistant to heat.  You are not converting much of the seashell material, in a spoon, over a candle sized flame, even if its hot enough.  It would take hours in a silica brick kiln.  Ps calcium hydroxide is very slightly solube.  You can buy lime, CaO, at the garden store.  It is also practically insolube.  But you will get as much CaOH this way as with your process.

[AWK]

K₂SO₄ may be also in garden store (the best potassium fertilizer for roses).

[Enthalpy]

A charcoal oven (not a spoon over a candle) decomposes calcium carbonate to CaO which reacts violently with water to give Ca(OH)₂ used in hydraulic lime and Portland cement.

So while buying lime is obviously easier and cheaper, making it would still be low-tech and a funny re-enactment of historic processes.