dissolving Ammonium Thiosulphate

Discussion in 'B&W: Film, Paper, Chemistry' started by don sigl, Sep 21, 2006.

  1. don sigl

    don sigl Member

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    I saw that the PF now carries ammonium thiosulfate in powdered form. Purchasing the powder is much more economical than shipping a gallon of 60% solution. Des anyone know if I will run into issues when mixing my own 60% solution? How easily does the powder form dissolve in water?

    Regards,
     
  2. Ole

    Ole Moderator Staff Member Moderator

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    It dissolves very easily. Just remember that a 60% solution is super-saturated: It's full of gunky undissolved stuff. Just like TF-4 concentrate, in fact...

    My main use of the powder has been in the "addon processing" - develop in very dilute developer (Rodinal 1+100 or more, Neofin, Beutlers, 1/2 strength FX-2 and similar), then instead of stop and fix, I just dump in a few teaspoons of ammonium thiosulfate dissolved in a little water. Works like a dream, and is great when I need to cut down on processing times.
     
  3. Robert Hall

    Robert Hall Subscriber

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    I get the stuff in 50kg containers. (about 105lbs) It saves me a fortune on fix.

    I warm up the water to around 25C and just keep mixing until it wont mix anymore. I store that in gallon containers until needed. ( I add a couple buffers to it as well, but it's fairly unnecessary)
     
  4. Roger Hicks

    Roger Hicks Member

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    The classic trick is to put the thiosulphate in a cloth bag suspended in the top of the vessel and leave it overnight; it will have dissolved in the morning. I have to admit this is hearsay only so I do not know if it works, but it should for any reasonable concentration.

    Where 60% is a reasonable concentration or not is another matter. I assume you dilute the stuff for use so why not mix it at working strength?

    Cheers,

    Roger (www.rogerandfrances.com -- look at the free 'hints and tips' module in the Photo School for other idea).
     
  5. Photo Engineer

    Photo Engineer Subscriber

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    Remember that when you add it to water, it will get cold. Hypos in general are endothermic, or that is, they absorb heat. That is why you start with warm water to mix hypo from scratch.

    PE
     
  6. Gerald Koch

    Gerald Koch Member

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    I seem to remember that the anhydrous thiosulfates are slightly exothermic when being dissolved. This is in contrast to sodium thiosulfate pentahydrate which is definitly endothermic. However, it has been a long time since I used any anhydrous ammonium thiosulfate. I do remember that this salt will absorb water from the air and harden like concrete. It is very important to keep it well closed.
     
  7. Photo Engineer

    Photo Engineer Subscriber

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    Gerald, from my experience, no thiosulfate is truly anhydrous! Open the bottle of "anhydrous" hypo and it is hydrated to the extent of the humidity of the packing plant.

    Fortunately, it is rather dry in Montana, where the Formulary is located.

    PE
     
  8. Ole

    Ole Moderator Staff Member Moderator

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    Even in wet and humid Western Norway, I haven't had any problems with the anhydrous thiosulfates clumping. The sodium thiosulfate pentahydrate, however...

    I think Gerald's correct, and it's the pentahydrate that's endothermic on dissolving. Anhydrous ammonium thiosulfate seems to be slightly exothermic, although I have no measurements to back this up. Just that it seems about "normal" when I mix a little of it in a little water.
     
  9. don sigl

    don sigl Member

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    Hmmm .... working srength is 4:1. I guess I could just mix it by the gallon that way.
    Good idea

    Thanks
     
  10. TonyPeers

    TonyPeers Member

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    ammonium thiosulphate powder, here in the UK?

    Hi, I'm looking for some ammonium thiosulphate powder - does anyone know of a supplier here in the UK?
    Kind regards
    Tony