Did I just re-compound separated hypo?

Discussion in 'B&W: Film, Paper, Chemistry' started by Tom1956, Aug 21, 2013.

  1. Tom1956

    Tom1956 Inactive

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    So I have this big jug of off-brand rapid-fixer concentrate. Concentrated to be mixed 1:3-4 for film and 1:7 for paper. The big jug of concentrate is quite old and has a pretty fair amount of sulfur-depositing on the inside of its plastic jug. And it smells pretty "stinky". Not totally ripe, but still smelly. Anyway, I had tried diluting some, and each time it wold precipitate what I guess was pure sulfur. And the diluted solution still smelled stinky.
    So I followed a tip I saw here and bought a 2 pound bag of tech-grade sodium sulfite and mixed 18 grams of it into 16oz of the concentrate. Then I poured in 48 ounces of water. Next I poured in 1 1/2 ounces of the hardener that came with it.
    And guess what? It's clear as a bell and smells like any other fresh fixer I ever smelled. Seems perfect. I'd be interested to know if I forced separated compound components back into compound? In other words, did I drive the sulfur back into sodium thiosulfate again? I can't recall enough of my college chemistry to figure it. But I do think I've re-claimed several gallons of free fixer, otherwise destined to be thrown out.
     
  2. Gerald C Koch

    Gerald C Koch Member

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    An acidified solution of thiosulfate is unstable and will eventually throw down a precipitate of sulfur. This reaction is called sulfurization. To slow this process down sodium sulfite is added to the mix. It will combine with the sulfur and produce thiosulfate ion.

    SO3-2 + S --> S2O3-2

    While it appears that you have resurrected the fixer for now remember all the sulfur on the sides of the container. Fixer is cheap but film and paper is expensive so this is really a false economy. The chemical balance of the fixer has been compromised. I would toss it.
     
  3. clayne

    clayne Member

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    I've used sulfured out fixer before. It does nothing negative as long as the fixer still has capacity.
     
  4. Gerald C Koch

    Gerald C Koch Member

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    It is fallacy of logic to base a conclusion on negative results and yet we see it over and over again on APUG. In fact this practice even has a name argumentum ad ignorantiam. No offense, but never personally having a problem with using spoiled fixer does not mean that there cannot be problems.
     
  5. Tom1956

    Tom1956 Inactive

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    Well I guess I'll have to look at it this way--I'm just going to be fooling around with X-Ray film, and the little bag of sulphite I got off EBAY SEEMS to have worked a miracle on this old smelly fixer concentrate, so I'm going to use it. I'll just go by the old rule of fixing for twice the time it takes to clear, and that'll have to be that. My little machine shop still hasn't had that "summer of recovery" I've heard about. Sure does look and smell like a fresh batch of Kodak Fixer as I remember it. We'll see.
     
  6. clayne

    clayne Member

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    Okay so explain with theory what the excess sulfur (that has solidified) is actually going to do.
     
  7. Tom1956

    Tom1956 Inactive

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    As the OP, I'm happy with GCK's explanation as I seem to be with any of his posts. But since I'm just tinkering around with x ray film, I'm confident this fixer will get me by. When I get tired of it, I'm liable to play with my RC planes or restore another radio or something.
     
  8. Gerald C Koch

    Gerald C Koch Member

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    The most obvious problem would be if some of the sulfur adhered to the emulsion. To avoid this the solution would have to be carefully filtered using laboratory grade filters. A slow and tedious process since their action is slow. Using something like coffee filters will just not work, they are just too porous.

    Adding sodium sulfite works best when the sulfur is in a colloidal state appearing as a white milkiness. When the particles appear yellow they are much larger in size and conversion back to thiosulfate is much slower. Once fixer starts to sulfurize things get worse very quickly.

    Two things favor sulfurization. The pH of the fixer and the ambient temperature where it is stored. The lower the pH the faster the reaction. Fixer should be stored in a cool but not cold place.

    As I said the risk of ruining an important film or a print is just too much of a chance to take. If the film is not important then there is no problem.
     
    Last edited by a moderator: Aug 22, 2013
  9. Tom1956

    Tom1956 Inactive

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    Thanks Gerald. The thing that struck me and drove me to start the thread is how totally crystal clear the working solution ended up being--and smelling. Not a hint of sediment. Like a miracle, because before I stirred the sulphite into the concentrated stock, it had a fair amount of (sulfur?) floating around. And if I tried making a working solution out of it ,the bottom 25% of the working solution would cloud up, and if I filtered it, it would just do it again, and again, till the whole gallon was gone. Now it's like brand new, and smells perfect. I just didn't expect such a drastic change.