Kodak HCA formula

Discussion in 'Kodak' started by Alessandro Serrao, Aug 13, 2005.

  1. From the Kodak MSDS for HCA there is:

    Weight % Components (CAS-No.)
    75-80 Sodium sulphite (7757-83-7)
    15-20 Sodium metabisulphite (7681-57-4)
    1-5 Sodium citrate (68-04-2)
    1-5 Ethylenediaminetetraacetic acid tetrasodium salt 64-02-8)

    and this refers to the package. So the quantities must be divided by 5
    to obtain the quantites for the working solution so:

    20g sodium sulphite
    4g sodium metabisulphite
    1g sodium citrate
    1g EDTA
    1l water

    so my question is this: what is the function of sodium citrate?
    Can I omit it and only use the first two chemicals in my home made hca
    working solution as well?
     
    Alessandro Serrao, Aug 13, 2005
    #1
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  2. Alessandro Serrao

    nailer Guest

    buffering and complexing. you can use sulfite with EDTA salt only.




    On Sat, 13 Aug 2005 11:45:09 GMT, Alessandro Serrao

    * From the Kodak MSDS for HCA there is:
    *
    *Weight % Components (CAS-No.)
    *75-80 Sodium sulphite (7757-83-7)
    *15-20 Sodium metabisulphite (7681-57-4)
    *1-5 Sodium citrate (68-04-2)
    *1-5 Ethylenediaminetetraacetic acid tetrasodium salt 64-02-8)
    *
    *and this refers to the package. So the quantities must be divided by 5
    *to obtain the quantites for the working solution so:
    *
    *20g sodium sulphite
    *4g sodium metabisulphite
    *1g sodium citrate
    *1g EDTA
    *1l water
    *
    *so my question is this: what is the function of sodium citrate?
    *Can I omit it and only use the first two chemicals in my home made hca
    *working solution as well?
     
    nailer, Aug 13, 2005
    #2
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  3. Alessandro Serrao

    dan.c.quinn Guest

    The citrate, today's Calgon, and the EDTA complex
    with impurities in tap water. I've very hard tap water
    but use distilled for processing.
    Sulfite alone will do for a somewhat more alkaline
    HCA. Meta or just bisulfite, same thing. Dan
     
    dan.c.quinn, Aug 13, 2005
    #3
  4. You can probably leave out the EDTA and Citrate if the
    working solution is used only once. Both are there to
    prevent deposits of minerals on the emulsion. The research
    paper does not discuss this.
    KHCA is a buffered solution of Sodium Sulfite. It is
    buffered to neutral pH, according to the Kodak research
    paper describing it the pH point was chosen to be:
    1, Above the isoelectric point of photographic gelatin.
    2, To minimise swelling and hense the diffusion path.
    3, A point where the hardening of white alum is not
    destroyed by where the binding effect of the alum on hypo no
    longer takes place.
    The first is important because when the gelatin is on the
    acid side of its isoelectric point it tends to bind hypo and
    fixing complexes.
    The approximate formula for KHCA is:

    Sodium Sulfite, dessicated 100.0 grams
    Sodium bisulfite 20.0 grams
    Sodium citrate 5.0 grams
    EDTA 5.0 grams
    Water to make 1.0 liter

    For use add 1 part working solution to 4 parts water.
    A plain 2% solution of Sodium Sulfite works where the pH
    buffering is not important.

    Note that the proportions given in MSDS are very
    approximate and that some ingredients may not have to be
    listed. An MSDS can give you a clue about what is in a
    material but not its exact formula, in fact, it can be
    misleading about this. Keep in mind that an MSDS is a
    _legal_ not a technical or scientific document.
     
    Richard Knoppow, Aug 13, 2005
    #4
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