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  1. #1
    skahde's Avatar
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    Quote Originally Posted by jdef
    Anyone know what adjustments were made?
    May I guess? The Phenidon in the original formula limits the shelflife of the developer once dissolved. They may have replaced it with something more stable like Dimezone-S or found out how small the speed-loss is when using Metol instead of Phenidon.

    Stefan

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    Quote Originally Posted by skahde
    May I guess? The Phenidon in the original formula limits the shelflife of the developer once dissolved. They may have replaced it with something more stable like Dimezone-S or found out how small the speed-loss is when using Metol instead of Phenidon.

    Stefan
    I doubt that they would use metol since it's expensive and needed in 10x the quantity of phenidone.

  3. #3
    ann
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    why not just call and ask. they are always very helpful

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    As long as the batch to batch consistency is there, I'm just happy the stuff works so well. Much better than PMK, especially with minimal agitation. Don't worry, be happy. tim

  5. #5
    skahde's Avatar
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    Quote Originally Posted by john_s
    I doubt that they would use metol since it's expensive and needed in 10x the quantity of phenidone.
    John, is that why Kodak doesn't sell D76 anymore ? Seriously, the difference would make 40 ct per 10l working solution if the Phenidone was free. Getting a stable liquid product that is more readily accepted by clients as there is no need to handle dry pyrocatechin would more than make up for that.

  6. #6

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    Quote Originally Posted by jdef
    I saw this at Photographers Formulary's website:


    Anyone know what adjustments were made?

    Jay

    My original formula for Pyrocat-HD called for adding 100 grams of potassium carbonate to 100 ml of water to mix Stock Solution B. That produced a total amount of Stock B of about 135 ml, which amounted to a 75% potassium carbonate solution.

    The original Formulary dry kits made a mistake and called for mixing 100 grams of potassium carbonate in water to make 100 ml of Stock B solution. This would be a 100% solution of Stock B. This made the working solution slightly more energetic, a minor problem. But a bigger problem was that some people had trouble getting the potassium carbonate into solution.

    Formulary corrected this discrepancy in the liquid kit. They were also alerted to a change in the formula I made in substituting sodium metabisulfite for sodium bisulfite, and presumably made that change as well.

    I doubt very much they would have substituted metol for phenidone without my knowledge since this substitution is far from inconsequential, and I have stated many times that I consider the metol formula a variant.

    Sandy

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    Donald Qualls's Avatar
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    Umm. Sandy? Wouldn't those carbonate solutions be 7.5% and 10% respectively? Equivalent to 75 g/L vs. 100 g/L?
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

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    Quote Originally Posted by Donald Qualls
    Umm. Sandy? Wouldn't those carbonate solutions be 7.5% and 10% respectively? Equivalent to 75 g/L vs. 100 g/L?
    There is a mistake in that it should have read 100 grams of potassium carbonate in 100 ml of water! I will go back and edit the message.

    Sandy

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    From Sandy, above....Formulary corrected this discrepancy in the liquid kit. They were also alerted to a change in the formula I made in substituting sodium metabisulfite for sodium bisulfite, and presumably made that change as well.

    It's probably a typo, but the liquid kit I got from them a few weeks ago didn't list either bisulfite or metabnisulfite in the formula on the included instruction sheet.

  10. #10

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    Quote Originally Posted by sanking
    My original formula for Pyrocat-HD called for adding 100 grams of potassium carbonate to 100 ml of water to mix Stock Solution B. That produced a total amount of Stock B of about 135 ml, which amounted to a 75% potassium carbonate solution.

    The original Formulary dry kits made a mistake and called for mixing 100 grams of potassium carbonate in water to make 100 ml of Stock B solution. This would be a 100% solution of Stock B.
    I've always wondered about the % values you've mentioned with these solutions, so I finally got around to looking it up.

    According to both my CRC Handbook of Chemistry and Physics, 32nd Ed., and Lange's Handbook of Chemistry, 8th Ed., they are both in agreement in their descriptions of % solutions of Potassium Carbonate.

    Sandy, what you have been calling a 75% solution of K2CO3, the CRC and Lange's both call a 50% solution. If you think about how you have taken 100g of K2CO3 and then added 100 ml of water, which weighs pretty close to 100g, can be thought of as taking 1 part and then adding another part to it, giving a total of 2 parts. So that solution, which has 1 part of solid in it, would be a 50% solution, not 75%.

    As you described, with your 100 g of K2CO3 and 100 ml of water, you ended up with "about 135 ml" of solution. If we take the 100 grams K2CO3 and divide it by our 135 ml solution volume, you will get a concentration of 0.74 g/ml. The CRC says that a 770g/L solution, which is nearly equivalent to our 0.74 g/ml (which equals 740 g/L) solution, is a 50% solution. This pretty much confirms the calcs in the previous paragraph.

    I'm sure that's where you're getting confused, but the nomenclature for percent solutions is not equivalent to g/L solutions.

    So your original instructions of 100 g K2CO3 dissolved into 100 ml water is actually a 50% solution (1 part + 1 part), and not a 75% solution - even though it has a concentration of about 0.75g/ml.

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