Re: Potassium Oxalate

From: Sandy King ^lt;[email protected]>
Date: 09/15/04-04:34:41 PM Z
Message-id: <a0602040dbd6e72730677@[]>

Hi Marek,

Thanks for your comments, and thanks to all the
others who responded today to my questions about
potassium oxalate and oxalic acid.

The potassium oxalate solution that I mixed is
about pH 5.4 and in printing works exactly like
the old solution that I have been using in terms
of speed, exposure scale and tone.

But what about long term storage of potassium
oxalate solutions? Does the pH change over time?
I ask because I have an old bottle of the stuff,
stored partially full in a glass bottle, and
when I checked it the pH was over 8. Is it to be
expected that the pH increases with time, and if
so, should this be of concern?


>By using your recipe you have a fair excess of oxalic acid (about 17%),
>which is not that soluble. You can add some more potassium carbonate (as I
>noted, 10 maybe even 15 grams) and still have about 5% excess oxalic acid.
>Typical POTA solution should be on the acidic side.
>By adding some sodium carbonate you have created mixture of potassium and
>sodium oxalate, with really a small amount of sodium, inconsequential for
>Pd development (that would be my guess, I have not tried that trick yet).
>Sodium oxalate is not very soluble, especially in cold solution. If you
>have added more then a few grams it might crystallize from the solution.
>> I separated the clear potassium oxalate solution
>> from the undissolved stuff at the bottom and put
>> it aside. I then added about 100 gs of water to
>> the undissolved junk and stirred. But it still
>> did not dissolve, so I then added some sodium
>> carbonate (by mistake since I meant to add
>> potassium carbonate). There was a lot of fizzing
>> and when it stopped everything was in solution.
>> But what do I have? Sodium Oxalate, or a mixture
>> of sodium and potassium oxalate?
>> Sandy
>>>I used the anhydrous variety of potassium carbonate.
>>>Thanks for the information about concentration.
>>>I will add some water to the solution and see if
>>>the stuff at at bottom dissolves.
>>>>What form of potassium carbonate did you use? If it is anhydrous, then
>>>> you
>>>>are about right, you can still add another few grams of potassium
>>>>carbonate, say 10 grams. If you used hydrated potassium carbonate, then
>>>>your proportions are off. By my estimation your solution is about 1.0M.
>>>> I
>>>>don't find any benefits using solutions more concentrated then 0.9M (im
>>>> my
>>>>practice, pritning Pd), so you can add some water to it (50-100cc).
>>>>You should not have any undissolved stuff.
>>>>Marek Matusz
>>>>> I mixed up a solution of potassium oxalate
>>>>> following directions provided by Nzé Christian. I
>>>>> added 130 gs of oxalic acid to 500 ml of water,
>>>>> mixed until dissolved, and then added 100 gs of
>>>>> potassium carbonate, and finished by adding
>>>>> another 15 gs of potassium carbonate, and finally
>>>>> I topped off the solution to one liter. Distilled
>>>>> water was used.
>>>>> The solution works fine for printing but there is
>>>>> still some junk at the bottom of the container
>>>>> that has not dissolved. What did I do wrong? Do I
>>>>> need to add more water, increase the temperature
>>>>> of the mix, or other?
>>>>> Sandy King
Received on Wed Sep 15 16:35:07 2004

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