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  1. #11
    gainer's Avatar
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    Quote Originally Posted by Kirk Keyes View Post
    Pat - Hardy and Perrin aside, a pinch of sulfite, added before the metol is added to the solution, will consume the small amount of oxygen dissolved in the water. (Cool water will have only about 8-10 mg/L of dissolved oxygen.) Since there is very little oxygen left in the water after the sulfite dissolves, there will be nothing there to oxidize the metol.

    So which approach is better?
    The oxidation to be concerned about here is that which may have been present at the start. It is not the oxidation that might occur in solution. Granted, it might be quite small in today's product, but who knows? It is the fact (not mine, but what I read in The Theory of the Photographic Process) that whatever amount of Metol may already have oxidized before starting the preparation may be fixed as the sulfonate that I have assumed was the reason for the recommendation by Hardy & Perrin for that deviation from the usual practice of a pinch of sulfite added with the Metol. It's not really much of an inconvenience. It may be that the Q will later revive even the sulfonate. I'm just guessing that it does not . I measured the pH of the solution of Metol in water to be about 5. I will measure it again with the pinch of sulfite. I just thought it a curiosity that Hardy & Perrin used that order of mixing without explaining why, as if everyone else already should know.
    Gadget Gainer

  2. #12
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    PS. A small pinch of sodium ascorbate would be even better, as it restores oxidized Metol to its original form without forming the sulfonate, according to what I have read. Anyway, it might be worth considering if the Metol is very old.
    Gadget Gainer

  3. #13
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    Quote Originally Posted by gainer View Post
    PS. A small pinch of sodium ascorbate would be even better, as it restores oxidized Metol to its original form without forming the sulfonate, according to what I have read. Anyway, it might be worth considering if the Metol is very old.
    Good idea! Thanks for the suggestion.

    just to make sure I understand correctly, you're suggesting the following order (e.g. for D76)...
    1) a pinch of ascorbate (would Ascorbic acid from the health food store also work?)
    2) the metol
    3) the Hydroquinone (?)
    4) sulfite (or, Borax...or does it even matter at this point?)
    5) borax
    Last edited by BradS; 06-05-2009 at 01:21 AM. Click to view previous post history.

  4. #14

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    Quote Originally Posted by Lee L View Post
    0.5 g of Sodium Bisulfite rather than 0.5 g Sodium Metabisulfite
    Lee
    One hundred grams of sodium sulfite. One half gram of
    either of the two above. Must be a misprint. Dan

  5. #15
    Ian Grant's Avatar
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    No it's correct. Sodium Metabisulphite is often used in small quantities in developer formulae. In theory if you use bisulphite instead you should add slightly more as it's not quite the same. I found a Kodak research article recently in a BJP Almanac (late 40's/early 50's) that compared the two and gave the suggested equivalents, the book's in the UK but I may have scanned the article. The difference is generally around 3-4% more Bisulphite is need compared to Metabisulphite.

    I have 6 other film developers in my database using 0.13 up to 1 gram per litre of film developer, these are Ilford, Crawley and Agfa Ansco developers, (4 are 0.5g or less).

    The importance of the metabisuphite is the free SO2 it gives off, it's often used to stabilise commercial powdered developer - used in Part A with the developing agents.

    Ian
    Last edited by Ian Grant; 06-05-2009 at 05:44 AM. Click to view previous post history. Reason: typos

  6. #16
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    Quote Originally Posted by BradS View Post
    Good idea! Thanks for the suggestion.

    just to make sure I understand correctly, you're suggesting the following order (e.g. for D76)...
    1) a pinch of ascorbate (would Ascorbic acid from the health food store also work?)
    2) the metol
    3) the Hydroquinone (?)
    4) sulfite (or, Borax...or does it even matter at this point?)
    5) borax
    1/2 level teaspoon of ascorbic acid + 1/4 tsp baking soda in a little water. Let the effervescence subside. Add this to the Metol solution. You probably dont need all the ascorbate, but I doubt it will make a noticable difference.

    In fact, if you run out of hydroquinone, you can try this: multiply the required amount of hydroquinone by 1.6 to find the amount of ascorbic acid. Multiply that amount to get the required amount of baking soda. Mix these amounts in water , Use a big container,but not any more than half the water you're going to use to make the developer. It's going to fizz a lot. When it quits fizzing, dissolve the Metol, then anything else that needs to go in and enough water to bring the volume up to total. You can try this sometime when you have time to play. It will substitute about the same number of molecules of sodium ascorbate for the hydroquinone.
    Gadget Gainer

  7. #17
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    BIG BOO BOO!
    Multiply the calculated amount of ascorbic acid BY 0.48 to get the amount of baking soda. By baking soda I mean, of course, sodium bicarbonate like you take for bellyaches such as I sometimes give people.
    Gadget Gainer

  8. #18
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    Quote Originally Posted by Ian Grant View Post
    The pinch of sulphite first does help the metol to dissolve, but then with a commercially packaged developer like D76 everything is already mixed together before you dissolve them. So it's not essential.

    Ian
    I have not found any difficulty in dissolving 2 grams of Metol in 100 ml water at room temperature. If my explanation of the mixing instructions given in Hardy & Perrin is not the right one, what is? They gave none in that book, but may have in another publication.

    Maybe Metol available in the 30's did have a possible oxidized component. Oxidized Metol is a development inhibitor. Sulfite converts it to the sulfonate, which at least is a weaker developing agent. Hydroquinone + sulfite regenerates oxidized Metol, as does an ascorbate. If their method is no longer needed, it still might do some good and no harm. There is no appreciable increase in time required for preparation.
    Gadget Gainer

  9. #19

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    Quote Originally Posted by Ian Grant View Post
    Sodium Metabisulphite is often used in small quantities
    in developer formulae.
    The importance of the metabisuphite is the free SO2 it gives off,
    it's often used to stabilise commercial powdered developer -
    used in Part A with the developing agents. Ian
    SO2, sulfur dioxide, a gas. A bisulfite when moist, as it may
    become with powdered commercial developers, acts like any
    sulfite to preserve. Why the BIsulfite is still a mystery. Free
    sulfur dioxide, sulfite or bisulfite, is unlikely because it
    would take quite an acidic environment to cause it's
    release. Over acidic stop baths can cause it's
    release. Dan

  10. #20
    Ian Grant's Avatar
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    Metabisulphite is used to control the pH, the SO2 forms sulphurous acid in solution, in combination with Sulphite it also has a buffering effect.

    The Sulphite/Metabisulphite buffer range is between pH 8 and pH 6.5, becoming more acidic as the proportion of Metabisulphite is increased, this is compared to the Borax/Boric Acid buffer range of pH 9.2 to pH 8.

    As a preservative Metabisulphite is many times more effective than Sulphite., which is why it's used in the food trade and wine making.

    Ian

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