Making Crystalline Potassium Carbonate

Saganich · Aug 21, 2008

After playing with D23 with borax, Sodium carbonate, Kodalk, glycin, for some time now I plan to mix-up some Crawley FX-2 and try some of the variations cited for solution B.

I read that I can make potassium carbonate crystalline by dissolving potassium carbonate anhydrous in seltzer and drying it out in low heat, thus reforming into the crystalline which will include Potassium bicarbonate. Is this correct.

Thanks

Ian Grant · Aug 21, 2008

Saganich said:
I read that I can make potassium carbonate crystalline by dissolving potassium carbonate anhydrous in seltzer and drying it out in low heat, thus reforming into the crystalline which will include Potassium bicarbonate. Is this correct.
Thanks

It's rather stupid because Crawley suggests using anhydrous Potassium Carbonate. Some US authors converted the formulae to the Crystalline form.

Just use the anhydrous form. The ratio is 1 anhydrous : 1.13 crystalline, so just divide a crystalline weight by 1.13

Ian

Saganich · Aug 21, 2008

From the 1961 article, "The use of potassium carbonate (crystalline) as in FX2 deserves comment. Potassium carbonate (cryst) B.P. K2CO3 1½H2O gives an individual type of alkalinity not matchable with any direct equivalent of potassium carbonate (dried)- as was observed by Dalzell in the twenties; the B.P. crystals must therefore be used in these formulae when specified. The type of alkalinity provided is useful, as it is in practice less energetic than the other carbonates (due to the formation perhaps of some restraining bicarbonate?) and therefore allows a fairly large concentration to be present, which stabilises the activity of the solution."

But that wasn't the question. I just want to know if the seltzer thing would get me a hydrate of some sort.

I did find some interesting substitutions for the Potassium Carbonate 1.5-Hydrate:

Sodium Carbonate, Mono 7g (Dignan Formula) [seems low to me]
Kodalk 112.5g (Anchell and Throop, film development cookbook pg 60)
Kodalk 150g (Bill Throop)
Potassium Carbonate, anh. 66.4g [crystal/1.13 as stated above]
Potassium Carbonate, anh. 62.7g [crystal/1.196 (calculation using formula weights)]
Potassium Carbonate, anh AND potassium bicarbonate (2%-10% ratio speculation)

dancqu · Aug 21, 2008

Seltzer? Schweppes? Dan

Photo Engineer · Aug 21, 2008

At equal molar concentrations and at the same pH value, it really does not matter whether you use Sodium or Potassium Carbonate. When you adjust the pH, the balance of Carbonate-Bicarbonate will be the same with either Na or K. And, with equal molar concentrations, then the amount of hydration is totally unimportant.

Early workers failed to record the moles used or the pH and thus make things like this impossible to figure out and reproduce. This makes the art of photography become a very fragile thing as we move into the future and the art is lost or the methods are lost.

Many things from 50 - 100 years ago are not able to be replicated today in the field of analog photography.

PE

eclarke · Aug 21, 2008

Saganich said:
From the 1961 article, "The use of potassium carbonate (crystalline) as in FX2 deserves comment. Potassium carbonate (cryst) B.P. K2CO3 1½H2O gives an individual type of alkalinity not matchable with any direct equivalent of potassium carbonate (dried)- as was observed by Dalzell in the twenties; the B.P. crystals must therefore be used in these formulae when specified. The type of alkalinity provided is useful, as it is in practice less energetic than the other carbonates (due to the formation perhaps of some restraining bicarbonate?) and therefore allows a fairly large concentration to be present, which stabilises the activity of the solution."

But that wasn't the question. I just want to know if the seltzer thing would get me a hydrate of some sort.

I did find some interesting substitutions for the Potassium Carbonate 1.5-Hydrate:

Sodium Carbonate, Mono 7g (Dignan Formula) [seems low to me]
Kodalk 112.5g (Anchell and Throop, film development cookbook pg 60)
Kodalk 150g (Bill Throop)
Potassium Carbonate, anh. 66.4g [crystal/1.13 as stated above]
Potassium Carbonate, anh. 62.7g [crystal/1.196 (calculation using formula weights)]
Potassium Carbonate, anh AND potassium bicarbonate (2%-10% ratio speculation)

Just curious, do you know the ph of your water??..EC

Saganich · Aug 21, 2008

So there isn't anything going on mystically with the Hydrated Potassium Carbonate? The more I read about the water of crystallization the more voodoo like it starts to sound. The one issue I still have is that the Bicarbonate speculation is just that, could there be something else going on here, perhaps the bonding in the crystal making for some reaction in the mix?

Photo Engineer · Aug 21, 2008

There is no mystery in the mix. Get the pH right and the molar concentration right and all will be identical for all practical purposes. But, to do that, you need the original, exact, and precise chemical formula used.

For example, from s statement you might use: " I used 27.6 grams of Na2CO3.2H2O / liter of water", I can exactly duplicate your result, but any vague hand waving with non-chemical terms render the formula less than precise and will be difficult to duplicate when that imprecise terminology goes out of style.

Today, many people cannot duplicate these types of formulas. It is becoming hard to find people who know that Oleum is the old word for concentrated sulfuric acid, and that Muriatic Acid is Hydrochloric Acid. I hope you see what I'm driving at.

PE

Saganich · Aug 21, 2008

Yes I see what your getting at but I'm just really curious about the statement

"Potassium carbonate (cryst) B.P. K2CO3 1½H2O gives an individual type of alkalinity not matchable with any direct equivalent of potassium carbonate.."

I mean it seems Crawley really thought something different was going on in the mix with the 1.5 hydrate versus the anhydrous equivalent.

Photo Engineer · Aug 21, 2008

Once it dissolves in water, it is totally hydrated and the formula is a mix of K+ ions, CO3= ions and HCO3- ions, totallly devoid of the relationship he describes. It is the pH that was unique here and he didn't know that, or didn't care. Using the right molarity of chemistry, Na+ ions could substitute for K+ ions and make no measurable difference all things being equal. Potassium vs Sodium does make a tiny difference in ionic strength, but this can be ignored for development. It usually cannot be ignored when making the emulsion.

PE

Saganich · Aug 21, 2008

So it would be useless to to spend $30 for 500g of K2NO3+1.5H2O because we don't know the pH he was working with. I see, oh well.

Photo Engineer · Aug 21, 2008

You could buy that, and pay the price, and if you duplicated his work, gram for gram, then it would work the way he described. Making it though is probably futile.

The reason is that if you use exactly what he specified, then it will work the same way.

PE

df cardwell · Aug 21, 2008

On the other hand, there is certain forgiveness in most developers, and FX2 is one of them.

It IS a remarkable developer, the balance with metol brings out a splendid potential for acutance, tonality, fine grain, and all that other stuff. But I think it is more important you find the way to work with FX2,than to worry about crystals vs anhydrous.

Saganich · Aug 21, 2008

Indeed, with two youngsters who has the time anyway! I still have a few months before my D23 supply exhausts. Marbles, I'll need marbles to keep the air out of the bottles, that glycin just loves the oxygen. Anyone have experience making marbles?

eclarke · Aug 22, 2008

Saganich said:
So it would be useless to to spend $30 for 500g of K2NO3+1.5H2O because we don't know the pH he was working with. I see, oh well.

Crawley is still around and some here can contact him. Why not just ask him?..EC

Photo Engineer · Aug 22, 2008

Bill Troop is in touch with him last I heard. Give Bill a shout. I just talked to Bill yesterday.

PE

Saganich · Aug 22, 2008

Fortunately I don't have trouble getting the 1.5H20 version of potassium carbonate so I'll likely mix up a batch as originally published and compare it with the other Part B versions...man sounds like allot of work. Keep me busy till the spring.

gainer · Aug 23, 2008

If you really feel you must have crystalline K2CO3, you can make a hot, saturated solution of any K2CO3 and let it cool. Crystals of (guess what?) crystalline K2CO3 will precipitate. Filter those and let them dry. However, your best accuracy in weighing would probably come from freshly dehydrated anhydrous K2CO3. As PE has tried to explain, one molecular weight of anhydrous K2CO3 and one molecular weight of the crystalline variety contain the same number of K2CO3 molecules. The molecular weights, of course, are different. Divide the molecular weight of the crystalline K2CO3 required by Crawley by its formula weight and multiply that number by the molecular weight of K2CO3 to get the formula weight of the anhydrous salt. I cannot see the mistery of the crystalline salt unless it is beacuse its molecular weight is more consistent. If your anhydrous carbonate is suspected of having become somewhat hydrated, put a stainless or pyrex saucepan of it on the stove and heat the bejesus out of it.

Photo Engineer · Aug 23, 2008

Yes, Patrick is right about heating to dry the carbonate, but be careful. Overheating will drive off CO2 and leave Potassium Hydroxide behind. I have known people to do this and the developer is very very over reactive.

PE

gainer · Aug 23, 2008

There is probably a temperature below which it is safe. I should think the temperature of decomposition would be in the CRC handbook. If I hadn't had a lapse of IQ, I would have looked it up. I'll be back in a minute.

gainer · Aug 23, 2008

I didn't find what I thought I was looking for. It seems to me that a double boiler with strong table salt solution in the bottom would produce a high enough temperature for the purpose without getting high enough to decompose the carbonate. Maybe the best way would be the silica gel packets, a gentle warming and a little shaking. Frankly, I don't believe that FX-2 is that critical, nor that the pH of a carbonate solution will change enough with small changes of concentration to be important. I think there is a borax-hydroxide buffer that will meet the requirements. Was Crawley trying to sell FX-2 by any chance?

gainer · Aug 23, 2008

I see that 1.5 times as much Kodalk has indeed been suggested as a substitute for the crystalline potassium carbonate. That in turn can be exactly replaced by a borax-hydroxide buffer which could be "tweaked" by more or less hydroxide.

In one table, the CRC handbook identifies a trihydrate, 2(K2CO3).3(H2O), which is obviously the crystalline form referred to.

Saganich · Aug 26, 2008

I would have to test it to make sure I end up with the 1.5H20 rather then the 3.0H20 variety. But, I just ordered some from fisher they have an inexpensive lab grade available. It will be interesting to see if there is any difference between the anhydrous and 1.5-hydrate. In theory there shouldn't!

Thanks for all insight.

dancqu · Aug 26, 2008

Saganich said:
I would have to test it to make sure I end up with
the 1.5H20 rather then the 3.0H20 variety.

Very likely the one rather than the other is dependent
upon the temperature of crystalization. If you've
not already, check for those temperatures.
Great purity may be possible. Dan

Making Crystalline Potassium Carbonate

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