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  1. #1
    Bruce Osgood's Avatar
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    Sodium Bisulfite > Sodium Metabisulfite

    I'm mixing a formula that contains 5g sodium bisulfite as a buffer to hydroquione. I don't have bisulfite but I do have metabisulfite. Is this apples and oranges or is there a conversion?

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    They are the same thing.

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    I've used the metabisulfite as a direct gram to gram substitute with no problem. Maybe a chemist can tell us the real story.
    juan

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    Bruce Osgood's Avatar
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    Quote Originally Posted by juan View Post
    I've used the metabisulfite as a direct gram to gram substitute with no problem. Maybe a chemist can tell us the real story.
    juan
    Thanks Juan,
    I'll go with 1 to 1 until I hear otherwise. Thank you,

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    Robert Hall's Avatar
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    They are not the same and the ph is different. I would ask Gerald Koch about this.
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    Why do you say that? When dissolved in water, metabisulfite forms bisulfite ion and they are the same thing. In amateur darkroom formulae I doubt anyone ever used pure sodium bisulfite in dry form as an ingredient; it's a misnomer.

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    Ole
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    In solution, they're identical.

    There's a difference in the crystal structure, but that doesn't matter at all as soon as it's dissolved.
    -- Ole Tjugen, Luddite Elitist
    Norway

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    Robert Hall's Avatar
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    Thank you for the clarification. It was my understanding that Metabisulfite had a lower ph, is this not true?

    thx
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  9. #9

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    When Kodak sold chemicals a mixture of sodium bisulfite and sodium metabisulfite was sold as sodium bisulfite. If you look at the MSDS for sodium bisulfite it is listed as 58 - 99% sodium bisulfite and 0 - 42% sodium metabisulfite. Pure sodium bisulfite is sold as a 40 - 45% solution rather than as a solid.

    Kodak recommended using the same amount regardless of which chemical the formula mentioned.

  10. #10
    Bruce Osgood's Avatar
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    Quote Originally Posted by Gerald Koch View Post
    ..............

    Kodak recommended using the same amount regardless of which chemical the formula mentioned.
    Works for me. Thanks to all who contributed.

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