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  1. #201
    Photo Engineer's Avatar
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    Go here: http://en.wikipedia.org/wiki/Ascorbic_acid and here: http://en.wikipedia.org/wiki/Sodium_ascorbate to see the structures of AA and Sodium Ascorbate. Your equation is not correct, as you cannot get free Boron and free Oxygen from this reaction.

    Sodium Metaborate + AA = Sodium Ascorbate and Boric Acid which lowers the pH. By lowering the pH, if there is enough Borate or Metaborate and if the pH is high enough, the equillibrium shifts and the buffering ability of the ingredients kick in to maintain the pH as much as possible. That is a simple explanation of what is going on.

    And, BTW, Borates are banned in many US Citrus states as Borates are toxic to Citrus trees.

    PE

  2. #202

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    Quote Originally Posted by Photo Engineer View Post
    Sodium Metaborate + AA = Sodium Ascorbate and Boric Acid
    I analyzed the above equation, and got this:

    3C6H8O6(AA) + 3NaBO2(metaborate) => 3C6H7NaO6(ascorbate) + H3BO3(boric acid) + B2O3
    Notice the extra 2 B's and 3 O's, which I combined into boron trioxide, which I doubt we'll actually get. Am I closer this time?

    Do you know if this reaction would occur when mixed in the PG? Or does it only occur in water? I'm wondering if we actually get ascorbate in the PG.

    Thanks as always,

    Mark Overton

  3. #203
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    Mark;

    This is a very complex reaction due to the presence of Borate which can make a variety of resultant anions. Don't worry about it. It is difficult for met to solve. I like easier equations. You are coloser, but the mixture will contain Ascorbates, Borates, Metaborates and the PG even makes some salts and esters with the materials present. You see, the Boric Acid will react with some of the metaborate and also with the OH ion present (being alkaline).

    Just measure the pH and be reassured that if you adjust it to where you want it to be, things should work out.

    Don't forget the toxicity of Boron containing salts to Citrus plants. IDK where you are located, but some of these salts are restricted in CA and FL.

    PE

  4. #204

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    Quote Originally Posted by Photo Engineer View Post
    Just measure the pH and be reassured that if you adjust it to where you want it to be, things should work out.
    Ron, Then that's what I'll do. I picked up the pH meter today.

    The formula I posted recently has a pH of 8.05. The test-strips said 7.8-7.9. You were right: They're significantly off.

    Quote Originally Posted by Photo Engineer View Post
    Don't forget the toxicity of Boron containing salts to Citrus plants. IDK where you are located, but some of these salts are restricted in CA and FL.
    With that encouragement, I decided to try removing the borate. The sulfite becomes the sole alkali, and I added ascorbic acid until the pH dropped to 8.0. Without the PG, here's the resulting simple 1-liter formula:

    Sodium sulfite ................ 90 g
    Phenidone ..................... 0.15 g
    Ascorbic acid ................. 3.5 g
    Target pH = 8.0. 7.5 min for TMY at 20C.
    That's it! And with a brief exam, I can't tell the difference between this formula and XTOL. I'm surprised. Has anyone before tried this simple PC-plus-sulfite formula?

    Mark Overton

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    Re the test strips and the pH-meter :
    Test strips 7.85 +- 0.20
    pH meter 8.05 +- 0.15

    Your test strips was definitely NOT significantly off, there is not anything in the whole world that is an EXACT measure, especially when it comes to pH measurements, electrode, exact mix, temperature.... a lot of stuff enters the equation here.

    I'd say your reasoning from the start based on the test strips was sound, and that you was in the ball park all the time.

  6. #206
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    Mark;

    The pH meter has some compensation for temperature and high salt content and therefore is more accurate than the strips which do not (obviously) have any means of compensation. The results of this measurement are as I suspected and the results are excellent. Congratulations.

    I'll bet the results make you very happy too! That is how I feel when something works out well. Enjoy.

    PE

  7. #207

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    Quote Originally Posted by albada View Post
    Ron, Then that's what I'll do. I picked up the pH meter today.

    The formula I posted recently has a pH of 8.05. The test-strips said 7.8-7.9. You were right: They're significantly off.



    With that encouragement, I decided to try removing the borate. The sulfite becomes the sole alkali, and I added ascorbic acid until the pH dropped to 8.0. Without the PG, here's the resulting simple 1-liter formula:

    Sodium sulfite ................ 90 g
    Phenidone ..................... 0.15 g
    Ascorbic acid ................. 3.5 g
    Target pH = 8.0. 7.5 min for TMY
    That's it! And with a brief exam, I can't tell the difference between this formula and XTOL. I'm surprised. Has anyone before tried this simple PC-plus-sulfite formula?

    Mark Overton
    The formula type is new to APUG as far as I know.
    But it is unbuffered, see posts #25 and #26 in this thread.
    It may oxidize to the more acidic(I think) dehydroascorbate and fall in pH.
    But one would have to do a long term comparative test with Xtol, both in contact with air,to see.

  8. #208

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    Quote Originally Posted by Photo Engineer View Post
    Mark;

    The pH meter has some compensation for temperature and high salt content and therefore is more accurate than the strips which do not (obviously) have any means of compensation. The results of this measurement are as I suspected and the results are excellent. Congratulations.

    I'll bet the results make you very happy too! That is how I feel when something works out well. Enjoy.

    PE
    How can you say that? Both measurements fall in roughly the same range; a couple of tenth's off which is insignificant is this context....

    He could have done just as well with a 15$ chinese pH meter, and changed it every year, ikf one was afraid that the *unusual environment* would eventually do in the cheap meter.....

    I don't think much was achieved here but demonstrating a tour-de-force that means nothing for the rest of us readers of this thread, this is supposed to be of value to rank amateurs and one need to have feet planted solidly on the ground.

    Sorry, but I have spent years around appartus like this in my work life, running everyday tests IRL...............
    Last edited by analog what is that?; 12-29-2011 at 12:55 PM. Click to view previous post history. Reason: typos

  9. #209
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    Quote Originally Posted by analog what is that? View Post
    How can you say that? Both measurements fall in roughly the same range; a couple of tenth's off which is insignificant is this context....

    He could have done just as well with a 15$ chinese pH meter, and changed it every year, ikf one was afraid that the *unusual environment* would eventually do in the cheap meter.....

    I don't think much was achieved here but demonstrating a tour-de-force that means nothing for the rest of us readers of this thread, this is supposed to be of value to rank amateurs and one need to have feet planted solidly on the ground.

    Sorry, but I have spent years around appartus like this in my work life, running everyday tests IRL...............
    With the exception of $ task-specific items, pH "test-strips" are a poor choice for any truly meaningful quantitative work. The investment in a quality meter will pay for itself by providing trustworthy accurate readings.
    - Ian

  10. #210

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    Well that is true, but NOT in this case, just look at the numbers............................

    If you think an expensive pH meter is a necissity or a requirement for doing this, you are doing your readers a disservice, given the state of "analog" photography, we most assuredly needs every experimenter and anyone willing to use film, to keep this thing alive.



 

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