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  1. #11
    Ole
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    A quick check is to heat the substance - nothing much happens to the anhydrous, while the pentahydrate will melt (actually dissolve in its own crystal water) at around 80 C.
    -- Ole Tjugen, Luddite Elitist
    Norway

  2. #12

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    I had a good experience with them as well. The nice thing about anhydrous is you are not paying to ship water. No problems dissolving to make my solution.

    Quote Originally Posted by Claire Senft
    I just bought a 30 pound pail of hypo from The Chemistry Store. The total cost including shipping was 69.00 USD and change. This is my second order from them and each order was handled very nicely. If there are two items a darkroom user is likely to use quite a bit of it would be sodium sulphite and fixer. I believe it makes economic sense to but these items in good size quantities.

    I checked my local pool supply store before ordering from TCS and they were not particularly competitive and the product included approximately 25% of other ingredients.

  3. #13

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    Quote Originally Posted by Ole
    A quick check is to heat the substance - nothing much happens to the anhydrous, while the pentahydrate will melt (actually dissolve in its own crystal water) at around 80 C.
    I just tested. I put a couple teaspoons of the sodium thiosulfate from The Chemistry Store in a microwave oven and heated it for close to a minute. The result was that part of it turned into a slushy mess and another part started looking awfully powdery. So, despite listing "sodium thiosulfate, anhydrous" as a synonym for what they're selling, I don't think TCS is really selling that variant -- or at least, what I got was pretty clearly the crystalline form. They've still got the best price on it I've seen on the Web, at least for the sorts of quantities amateur photographers are likely to need. If somebody else has definitely gotten the anhydrous form from them, then it seems that they're not being very consistent in what they ship.

  4. #14

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    You can melt metal in a microwave. Not a good test for melting point IMHO.

  5. #15
    Ole
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    Quote Originally Posted by avandesande
    You can melt metal in a microwave. Not a good test for melting point IMHO.
    That's what I was going to say - "testing" something in a microwave is close to worthless. You have absolutely no control over the temperature, even heating it over a candle is more predictable!

    You are not trying to melt it, but to allow it to dissolve in the water that is already in the crystal. So it's important that you don't heat it too much or you will boil off the water!

    Another way is to grind it in a mortar, or between two spoons, or similar. Sodium thiosulfate pentahydrate won't turn to powder, but to liquid!
    -- Ole Tjugen, Luddite Elitist
    Norway

  6. #16

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    Quote Originally Posted by Ole
    ...don't heat ...
    Cool it! Cool a spoon full in a small glass of room
    temperature water. Real Cool!
    While the penta will chill the solution the anhydrous
    will not. Dan

  7. #17
    Ole
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    Quote Originally Posted by Ole
    don't heat it too much ...
    No boiling, not room temp...
    -- Ole Tjugen, Luddite Elitist
    Norway

  8. #18

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    Quote Originally Posted by dancqu
    Cool it! Cool a spoon full in a small glass of room
    temperature water. Real Cool!
    While the penta will chill the solution the anhydrous
    will not. Dan
    FWIW, I just made some fixer (the citric acid variant of F24) with the sodium thiosulfate I got from The Chemistry Store. It chilled the water quite substantially when I added it, to the point that the originally room-temperature mixing vessel, holding what had been room-temperature water, ended up with condensation forming on it. Thus, I'm quite certain it's the crystalline form, although "anhydrous" is mentioned as a synonym on the TCS Web page.

  9. #19

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    What TCS sells is the pentahydrate. They are not unique in supplying a MSDS for the anhydrous form of a chemical while they sell a hydrated form. I have found that other suppliers do the same. In fact some suppliers of chemicals aren't sure just what they are selling. Part of the general dumbing down of the public as far as I am concerned.

  10. #20

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    Quote Originally Posted by Gerald Koch
    In fact some suppliers of chemicals aren't sure just
    what they are selling.
    That's easy to believe. I do feel safe buying from
    Photographer's Formulary. They are many years in the
    business of being a specialty supplier to darkroom workers.

    They have the anhydrous and the penta thiosulfates.
    Pay for three pounds of the penta or two pounds of the
    anhydrous. With the penta a pound of water is
    included at no extra charge. Dan

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