superadditivity phenidone/citric acid

Discussion in 'B&W: Film, Paper, Chemistry' started by RalphLambrecht, Jul 15, 2012.

  1. RalphLambrecht

    RalphLambrecht Subscriber

    Messages:
    8,255
    Joined:
    Sep 19, 2003
    Location:
    Florida
    Shooter:
    Multi Format
    is anyone aware of research conducted about the super aditivity between phenidone and citric acid. the knowledge would be importznt if one wants to substitute m an q developwrs with p and c. thanks in advance.
     
  2. Gerald C Koch

    Gerald C Koch Member

    Messages:
    6,337
    Joined:
    Jul 12, 2010
    Location:
    Southern USA
    Shooter:
    Multi Format
    I believe you mean ascorbic acid since citric acid is not a developing agent.

    Phenidone and ascorbate ion do form a super additive mixture. However what is envolved is not a simple substitution of ascorbic acid for hydroquinone. As has been mentioned several times on APUG the resemblence between these two developing agents is superficial and several adjustments must be made to a hydroquinone developer to convert it into an ascorbate developer. To mention a very important difference between the two developing agents, hydroquinone is a is an uncharged molecule while ascorbic acid in solution is a negatively charged ion. This has a important effect on the adsorption of the developing species on the silver halide grains. To explain what occurs is very complex and anyone interested should read up on the development process in particular the Charge Barrier Effect.
     
    Last edited by a moderator: Jul 15, 2012
  3. RalphLambrecht

    RalphLambrecht Subscriber

    Messages:
    8,255
    Joined:
    Sep 19, 2003
    Location:
    Florida
    Shooter:
    Multi Format
    indeed, i meant ascorbic acid, thanks for the correction.
     
  4. Alan Johnson

    Alan Johnson Subscriber

    Messages:
    1,536
    Joined:
    Nov 16, 2004
  5. RalphLambrecht

    RalphLambrecht Subscriber

    Messages:
    8,255
    Joined:
    Sep 19, 2003
    Location:
    Florida
    Shooter:
    Multi Format
    THAT'S WHAT I NEEDED. THANKS A BUNDLE!