Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,962   Posts: 1,558,318   Online: 1000
      
Results 1 to 7 of 7
  1. #1

    Join Date
    Sep 2010
    Shooter
    Multi Format
    Posts
    34

    Role of Aluminium Sulfate in Fixer

    I have a fixer that has the following composition:

    Ammonium thiosulfate, sodium bisulfite, ammonium bisulfite, sodium tetraborate, aluminum sulfate.

    My question is, is this a hardening fixer? If not, what is the role of aluminium sulfate? Thanks!

  2. #2
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,336
    Images
    148
    It is the hardening agent.

    Ian

  3. #3

    Join Date
    Sep 2010
    Shooter
    Multi Format
    Posts
    34
    Hi Ian,

    Thanks for your response. My follow-up question is, Why is the hardening agent not of the more common potassium/sodium alum form (i.e. potassium/sodium aluminium sulfate)? Do the components listed allow the formation of the more common alum form in the solution?

  4. #4
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,336
    Images
    148
    It's going to depend on what else is in the fixer. Sometime a formula is made up from components that react to form what's needed, Rodinal uses Potassium Metabisulphte and Potassium Hydroxide to form Potassium Sulphite (and water).

    So it's what the components form in equilibrium reactions in the final solution that's more important, without seening the entire list of components it's hard to be more precise.

    Ian

  5. #5

    Join Date
    Jul 2010
    Location
    Southern USA
    Shooter
    Multi Format
    Posts
    3,965
    It is the Al+3 ion which does the hardening. It really doesn't matter what salt supplies it. It can come from aluminum sulfate or from sodium aluminum sulfate. I suspect that the bottom line determines which one is used. Sodium aluminum sulfate is one of a group of compounds known as alums which are double salts. For example sodium sulfate plus aluminum sulfate. They exist as definite compounds in the solid state but dissociate in water into the component ions.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  6. #6
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,214
    Images
    65
    Quote Originally Posted by geyes30 View Post
    Hi Ian,

    Thanks for your response. My follow-up question is, Why is the hardening agent not of the more common potassium/sodium alum form (i.e. potassium/sodium aluminium sulfate)? Do the components listed allow the formation of the more common alum form in the solution?
    Alum is Potassium Aluminum Sulfate.

    http://en.wikipedia.org/wiki/Alum

    The hardening action of Alum is reversible.

    PE

  7. #7
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,336
    Images
    148
    When Aluminium Sulphate is used instead of Potassium Aluminium Sulphate (often called Potassium Alum) the hardener often contains some Sulphuric acid.

    It is possible as Gerald states to use an Alum like Sodium Aluminium Sulphate (Sodium Alum) in a harening fixer.

    The term Alum itself is used in different trades to signify quite different compounds so is quite unspecific.

    Ian



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin