Sodium Sulfite, Sodium Bisulfite, and Sodium Metabisulfite

Discussion in 'B&W: Film, Paper, Chemistry' started by Donald Miller, Mar 24, 2006.

  1. Donald Miller

    Donald Miller Member

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    Are any of these chemicals interchangeable in developer formulations? If so what are the relative amounts used in substitutions?
     
  2. john_s

    john_s Subscriber

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  3. sanking

    sanking Member

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    Yes, to some extent. Both sodium metabisulfite and sodium bisulfite are acidic and are used as a preservative in many two part developers (PMK, Pyrocat-HD, Rollo Pyro, etc.) In this application plain sodium sulfite is not interchangeable with metabisulfite and bisulfit.

    However, when dissolved in water (as in a working solution) both sodium metabisulfite and sodium bisulfite release sulfite ions. On a per gram basis, in this type of application, the ratio is about 13:10 sodium metabisuflite to sodium sulfite.

    But see Ryuyji's web page mentioned above for a more detailed discussion of the subject.

    Sandy



     
  4. Donald Miller

    Donald Miller Member

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    Thanks for the information. I will check it out.
     
  5. dancqu

    dancqu Member

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    They are all interchangeable only if the formula
    so states. Other wise only the two bisulfites
    are interchangeable.

    The two bisulfites are acid salts and the same save
    for the meta form being short one molecule of H2O.
    That is due to the loss of one H2O at the time of
    crystallization. Just add water and you've the
    bisulfite; Na2S2O5 + H2O = 2, NaHSO3.
    Strictly speaking the meta is a bit
    more of a concentrate.

    The sulfite is moderately alkaline while the bisulfites
    are moderately acid. They are all sulfites and so do act
    as preservatives. I've some phenidone concentrate
    using sodium bisulfite. Generally, an acid solution
    of a reducing agent will preserve better than
    an alkaline solution of same. Dan
     
  6. dancqu

    dancqu Member

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    The meta is not a bi nor a sulfite; Na2S2O5. Meta means
    a form more nearly anhydrous or lacking some water. Similar
    are the acids of boron, ortho, meta, and tetra. We use
    the sodium salts metaborate and tetraborate.

    By weight 190 parts of the metabisulfite equal 208 of the
    bisulfite. In solution the meta will hydrate, absorb H2O,
    and transform into a bisulfite.

    IIRC there seems to be some question as to what is
    in the bottle. Some years ago I read Ryuji's writings on
    the subject. He covers the subject in more detail. Dan
     
  7. sanking

    sanking Member

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    I have visited Ryuji's site and am aware of the the meta versus bisulfite issue.

    As for the ratio of sulfite ions released by sodium metabisulfite when dissolved compared to sulfite ions from sodium sulfite when dissolved, I believe that is correct.

    Sandy
     
  8. Ryuji

    Ryuji Member

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    Since my web site got mentioned... I'm in process of converting old static html based technical info pages to Wiki system similar to wikipedia. It's a lot easier for me to edit and update articles this way. (It's also easy to start writing something and expand later.) So when the link for old stuff goes away, try to search by keyword in the wiki page.