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  1. #21

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    Quote Originally Posted by Relayer View Post
    not agree - you forget about hydrolyze.
    You can certainly try mixing sodium carbonate and borax together in water but speaking as a chemist it's not going to make sodium metaborate.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  2. #22
    Photo Engineer's Avatar
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    During the war, Agfa used a Kodalk substitute. I would have to go back over a lot of notes to find this, but if you need it, I might be able to find it. A simple solution exists. I know that, but it is hidden in reams of notes. sorry.

    PE

  3. #23
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    Quote Originally Posted by Gerald C Koch View Post
    You can certainly try mixing sodium carbonate and borax together in water but speaking as a chemist it's not going to make sodium metaborate.
    There is little chance that sodium metaborate is actually present in substantial amounts at pH of 8.2. Let's look at an excerpt from this table of buffers:

    Buffer pH range
    Sodium tetraborate/ Hydrochloric acid 8.1 - 9.2
    Sodium tetraborate/ Sodium hydroxide 9.3 - 10.7
    Sodium carbonate/ Sodium hydrogen carbonate 9.2 - 10.8

    This table suggests that below pH of 9 there is an equilibrium between borax and boric acid, no matter which borate compound you started with, and that the carbonate won't interfere all that much. I seriously doubt that there would be a noticeable difference between NaOH+Borax and Na2CO3+Borax once the remaining compounds are added to make pH of 8.2.

    So, yes, you may be right in theory, Na2CO3+Borax don't make metaborate in aqueous solution, but they do make something which behaves very very similar to metaborate once pH is set below 9. Let's face it: all these recipes list metaborate because it is much easier to dissolve initially than borax or boric acid, not because of its pH buffer range.
    Trying to be the best of whatever I am, even if what I am is no good.

  4. #24
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    the darkroom cookbook3rd ed shows another substitution on page 329as sodium carbonate multiplied by 0.59. i never tried it though.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  5. #25

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    Quote Originally Posted by BradS View Post
    I had this same question some years ago....I'm not a chemistry person so, it took me several hours to figure this out but, here's the way I see it....

    2NaOH + Na2B4o7(10H2O) + 5H2O <-->> 4NaBO2(4H2O)

    2 mols lye + 1 mol Borax (in water) is equivalent to 4 mols Kodalk in water

    80g lye + 381.37g Borax (in water) is equivalent to 551.42g Kodalk in water.

    divide each of these by 5.5142 and we have:

    14.5g Sodium Hydroxide (Lye) + 69.2g Borax dissolved in water is equivalet to 100g of Kodalk (dissolved in water.


    Of course, you may wish to divide by 55.142 to get...

    1.45G Lye + 6.9g Borax (dissolved in water) is the equivalent of 10g of Kodalk dissolved in water.


    The difficulty with this whole approach is always measuring out the Lye accurately. It suck water out of the air so fast you can actually watch it gain weight on a scale.

    (EDIT: or, do as Ian suggests above!)
    You're NOT a chemistry person? Fooled me.

    Jon

  6. #26

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    Quote Originally Posted by Photo Engineer View Post
    During the war, Agfa used a Kodalk substitute. I would have to go back over a lot of notes to find this, but if you need it, I might be able to find it. A simple solution exists. I know that, but it is hidden in reams of notes. sorry.

    PE
    I'm very interested, too, if you could find your notes on that, please. Once we already touched this issue, but never came to exact formulas. Maybe the following quote will help you:

    http://www.apug.org/forums/forum37/5...-others-3.html

    "Quote Originally Posted by Photo Engineer View Post
    In den Begiebezustatze ist Borax-Ersatz je nach Saure bestimmung oder Borax mit Natrium Carbonate.

    During the war, Agfa could not get Borax from the US easily so they made a substitute. This quote above is directly from what I copied from an Agfa formula many years ago. It was published (AFAIK) in the FIAT reports.

    I hope I got that right.

    PE
    My quote is incorrect above due to my poor rememberance of German. The exact information was on two pages and I had to combine the two.

    Basically, they used Ersatz Borax or acid to adjust pH in solutions and the ersatz Borax was made from Sodium Carbonate and Bicarbonate or with Sodium Bicarbonate and Sodium Hydroxide. The acid used depended on the solution being adjusted.

    I looked up my notes again today to see if I could clarify this and use English which is a bit better than my German.

    PE "
    Last edited by Igor Savchenko; 07-21-2012 at 07:34 AM. Click to view previous post history.

  7. #27
    Rudeofus's Avatar
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    Igor: borax allows you to go acidic or caustic, see my table above. And as it just so happens, in caustic direction direction you cover about the same pH range as with carbonate/bicarbonate. For pH levels below 9, though, you will be out of luck, this borax ersatz will not help Relayer.
    Trying to be the best of whatever I am, even if what I am is no good.

  8. #28
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    Igor;

    After reading my posts, I remembered enough to say that Agfa used a mix of Carbonate + either bicarbonate or hydroxide, and they finalized the pH adjustment with an appropriate acid. So, knowing the pH was critical here as that was the aim point. The rest was merely the addition of carbonate to get close and then tweaking the pH. Once they had the pH right, they could then record how much of each ingredient they added and make that the starting point for the next run.

    This was not an exact science back then. In fact, their starting materials varied quite a bit and their description was quite vague. so is my memory, but this description and my two posts above that you refer to summarize things well.

    PE

  9. #29

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    Quote Originally Posted by Relayer View Post
    just make some experiment: in 1l of water at 32C dissolve 1.92g of Sodium carbonate. then add 6.92g of borax - its dissolved very quickly! solution is muddy, but clear after 2-3min. check pH - 9.2 at 24C. now put this solution in open bottle and will be recheck pH later
    recheck pH after 24 hour - still 9.1-9.2. any comments?

  10. #30

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    Quote Originally Posted by Rudeofus View Post
    ... he wants a buffer at pH 8.2 for a photographic developer.
    NO, he wants a substitute for sodium metaborate in DK-50 and DK-76 neither of which has a pH this low. It's interesting how threads veer off from the original post.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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