Citric acid stop bath crystals

Discussion in 'B&W: Film, Paper, Chemistry' started by Alessandro Serrao, May 23, 2009.

  1. Alessandro Serrao

    Alessandro Serrao Member

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    I think I've got gremlins in my cellar...
    Now I've got a problem with stop bath: I just mix Kodak Sb-8, that is 15g citric acid in 1lt of plain water. The day after I got many crystals of citric acid floating freely in the bottle and there's not any conceivable way of getting them back into solution...

    What the hell is this?

    It happens with distilled water and tap water with edta alike...
     
  2. amuderick

    amuderick Member

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    make the water warmer.
     
  3. Alessandro Serrao

    Alessandro Serrao Member

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    It's at 22°C
     
  4. Nathan Potter

    Nathan Potter Member

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    Heat it 50C and stir vigorously. How pure is your citric acid?

    Nate Potter, Austin TX.
     
  5. Alessandro Serrao

    Alessandro Serrao Member

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    It's reagent grade.
     
  6. john_s

    john_s Subscriber

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    A google search showed a couple of sites that say that approx 600g of citric acid is soluble in 1 Litre of water at 20degC.

    Something else is happening if 15g doesn't seem to be dissolving.
     
  7. Alessandro Serrao

    Alessandro Serrao Member

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    The weird thing is that those crystals keep coming back after all the citric acid is dissolved.
    It's like citric acid re-precipitates.

    However, to cut a long story short, I'll mix stop bath on a per session basis (3g/250ml)...
     
  8. tim_bessell

    tim_bessell Member

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    I regularly mix a 3% citric acid (30 g/1 Liter) clearing bath for Kallitype prints in room temperature (~20°C) distilled water and never had a problem. It dissolves fast and easily. I have never seen any crystals or precipitation.

    According to Wikipedia, the solubility of citric acid in water is 133 g/100 ml (22°C)

    What is the quality of you water?
     
  9. Ole

    Ole Moderator Staff Member Moderator

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    It can't be citric acid crystals, so it must be something else. I can't remember if there are any likely candidates among the citrates, but my guess is that something carried over from the developer is insoluble in acid solutions. Or something in your bottle...

    In other words, you're not giving us enough information.
     
  10. RobertV

    RobertV Member

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    15g/1 ltr is a quite normal (1,5%) stop bath. And indeed the solubility of Citric Acid in a liter water is very high so that can not be any problem at all.
    Somewhere there must be a contamination.
    Put those Gremlins back in the box where they can not disturb you. :D
     
  11. Alessandro Serrao

    Alessandro Serrao Member

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    I think you're right but I still cannot trace back the problem.
    Maybe it's some kind of bacterial growth, I've washed the bottle with quaternary ammonium salt and I've rinsed it well. Will see if it has solved the problem.
     
  12. dancqu

    dancqu Member

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    In the kitchen it is known as Sour Salt. Dan