sodium bisulfite precipate in fix

Discussion in 'B&W: Film, Paper, Chemistry' started by SHO.Z-S, Nov 11, 2012.

  1. SHO.Z-S

    SHO.Z-S Member

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    new to mixing my own chemistry

    mixing some f24

    sodium thiosulfate 240g
    sodium sulfite 10g
    sodium bisulfite 25g
    1 L

    everything goes fine until i add the sodium bisulfite which precipitates and doesnt seem to dissolve very much at all.
    happens with both tap water and distilled

    will the precipitate dissolve eventually or is there something wrong?

    thanks!
     
  2. Gerald C Koch

    Gerald C Koch Member

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    The first two ingredients should be dissolved in 800 ml of 150oF water The bisulfite should be dissolved in about 100 ml of cold water. When the thiosulfate mixture is cool slowly add the bisilfite solution with vigorous stirring. The solution is then made up to 1 liter. This method should be use when adding any acidic component (bisulfite, alum, acetic acid, etc) to a thiosulfate solution.
     
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  3. SHO.Z-S

    SHO.Z-S Member

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    so mix the hypo and sodium sulfite at 125-150ºF and then allow this solution to cool
    and mix the sodium bisulfite alone at 68˚

    and then mix both solutions together.
    correct?

    -i am currently working in low-temperature conditions.

    and thank you gerald!
     
  4. Gerald C Koch

    Gerald C Koch Member

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    Yes you qare correct. Unfortunately formulas often don't give mixing instructions and they can be important.
     
  5. SHO.Z-S

    SHO.Z-S Member

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    dear gerald,

    mixed again as per your instructions. now its cloudy. no more precipitate, but oddly milky.
    i did test a film leader and it cleared fully in under 45 sec, so it does work, but is questionable in 'consistency', all fixers ive used in the past are clear and one can see through them...

    thanks again for all your help man!
     
  6. Gerald C Koch

    Gerald C Koch Member

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    Sounds like there was a bit of sulfurization. This can happen when an acidic chemical is added to a thiosulfate solution. The thiosulfate/sulfite mixure must be cool and the bisulfite solution added slowly with constant stirring to prevent any local pockets of low pH from forming. The cloudy bath is still useable however.