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  1. #121
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    Rudi;

    With a straight reaction which is what takes place, you get 1 equivalent of AA and 1 eq of Phenidone. If it were catalyzed you might see 100 AA to 1 PD and the PD might be regenerated entirely. This is the case of AA + Iron + Oxygen. You get an Iron catalyzed decomposition of AA which is the bane of all AA developers.

    Unless you have a secret ingredient that stops this reaction.....

    PE

  2. #122

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    But in the end it has the effect of a catalyst.
    NO, in a catalytic readtion the catalyst remains unchanged. In the catalytic converter of a car the platinum catalyst can be extracted unchanged when the unit is discarded. It is not used up. Super additivity is NOT a catalytic reaction, the Phenidone or Dimezone does get used up. The regeneration of the Phenidone by the ascorbate is not 100% effective.

    When used alone ascorbate ion has a long induction period where no development appears to takr place. This is because it is a negative ion and other negatively charged developer ions behave the same. (An example would be the hydroquinone monosulfonate ion produced by the oxidation of hydroquinone in a sulfite solution.) Given time ascorbate will produce an image. Phenidone and its derivatives have no charge and act more quickly because they are not effected by the charge barrier of the silver halide grains.

    I might note that years ago I went around and around with Pat Gainer on this notion and was never able to completely dissabuse him of this idea. I finally gave up.
    Last edited by Gerald C Koch; 08-06-2012 at 03:55 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

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  3. #123
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    I should say right away that I am no chemist so what I say shall be taken with a big load of salt. Quoting straight from Wikipedia:
    Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself.
    Even if some of the Phenidone gets used up in the reaction, this is not a key feature of the reaction, and in fact we would all be a lot happier if the Phenidone would not get used up at all. Fact is that lots of silver ions get reduced per active molecule of Phenidone and fact is also that platinum catalysts in cars don't last forever.

    But anyway, if Jerry kindly provided me with a link to his exchange with Pat, we might save this forum from a pointless reiteration of arguments that have already been beaten to death. Maybe real chemists have a more precise definition of catalysts that I am not aware of and that would not cover a reaction like reduction of light exposed silver grains with Ascorbate in the presence of traces of Phenidone.
    Trying to be the best of whatever I am, even if what I am is no good.

  4. #124

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    What happens in a car and also with other metal catalysed reactions is that the catalyst eventually becomes poisoned and no longer works. It does not get used up.

    In metal catalysis the catalyst provides a substrate on which the reacting molecule is adborbed. During this adsorption the geometry of the molecule is changed making it more reactive. One can think of the process this way. Consider two muggers, the first (the catalyst) holds the victum down so the other one can get at his pockets more easily. The same thing happens in biochemistry with enzymes. They alter the shape of a molecule causing it to be more reactive.

    Fact is that lots of silver ions get reduced per active molecule of Phenidone
    This is true only because the ascorbate regenerates the Phenidone by reducing the oxiidized product back to Phenidone. As a result the ascorbate gets oxidized and used up. If you look in a book such as Mason the reactions involved are explained. If Phenidone were a catalyst there would no need for it to be reduced.

    Metol also forms a super additive mixture with ascorbate but is less effective since less of it is regenerated than Phenidone.

    Chemists don't hold a different definition of catalysis than other people they hold the only definition.
    Last edited by Gerald C Koch; 08-06-2012 at 06:29 PM. Click to view previous post history.
    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

  5. #125

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    Quote Originally Posted by Rudeofus View Post
    if Jerry kindly provided me with a link to his exchange with Pat, we might save this forum from a pointless reiteration of arguments that have already been beaten to death
    After so many years I have no idea on which thread(s) the exchange occurred. Gainer's argument always returned to saying that it looked like catalysis. Of course looking like something is not the same thing a being the thing.
    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. #126
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    Jerry is correct.

    My example is correct but misleading. I said "PD might be regenerated". Well, it is regenerated but not 100% due to possible alkaline ring opening so I picked a bad example. IDK the amounts of ring opening and regeneration. If you had Dimezone S there, it would be 100% regenerated. PD is partly regenerated and partly hydrolyzed upon oxidation.

    That is why I like Dimezone S. It is easier for me to predict.

    PE

  7. #127

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    Exciting stuff! And just what i need. Wonder how it works on delta 3200?

    Mark, once you get a formula with 99% tea, i think i will jump aboard and start doing some testing of my own. I just dumped over 3 liters of dead xtol.

  8. #128

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    Quote Originally Posted by Alan Johnson View Post
    Your precipitate may be glycol-borate complex ,we will never know.I don't think esters are formed at the mixing temperatures you use:
    http://www.chemicalforums.com/index.php?topic=41216.0
    For other PC developer PC-TEA when selecting development times for different films I have used a simple multiplier of Xtol time,is there any reason not to use this with one of the concentrates?
    Alan, thanks for the above link. Interesting! His symptoms are identical to mine, even though he's using a different glycol and borate. This gives me more motivation to replace the borate with TEA. BTW, that's what PE told me to do months ago. But I stayed with metaborate because it boosts the solubility of ascorbic acid in propylene glycol. Maybe I shouldn't have...

    The single multiplier will probably get you close, but I suspect that films will respond differently to the lower pH, resulting in a different multiplier for each film.

    Quote Originally Posted by AlbertZeroK View Post
    Exciting stuff! And just what i need. Wonder how it works on delta 3200?
    Mark, once you get a formula with 99% tea, i think i will jump aboard and start doing some testing of my own. I just dumped over 3 liters of dead xtol.
    I have the same motivation as you: I hate to discard aging XTOL. The 99% TEA arrives today, so I'll soon be trying it.

    Mark Overton

  9. #129

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    Quote Originally Posted by Rudeofus View Post
    I would like to know to which extent variations in composition have a visible effect on characteristic courve, grain, sharpness, etc. Since you have obviously done lots of experiments before you came up with your final result, could you comment on that? Would a 10% variation make a big difference or does it take much more before you saw anything different?
    An interesting question. I've found that 15% variation in sulfite makes little difference. But 10% too much Phenidone/Dimezone can increase grain noticeably. For a concentrate, it would be helpful if both sulfite and concentrate could be measured by volume, preferably with a set of kitchen measuring spoons (teaspoon/tablespoon) or perhaps a medicine measuring cup. Either way, the sulfite would be less accurate than the liquid due to variations in compaction and fineness of the powder. I think that if a formula can give good results within a +/- 15% error in sulfite, it'll be acceptable.

    Medicine measuring cups can be purchased in a 100-pack (!) for under $5 as in this example at Amazon. One advantage of these cups is that you can draw fill-lines at the correct levels with a black felt-tip marker, making measurement of arbitrary quantities easy.

    Mark Overton

  10. #130
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    Measuring viscous liquids by volume becomes tricky! Best to use a syringe from a pet store or vet, or use weight.

    As for the variations, you may see little visible difference with Sulfite unless you look at Grain or Sharpness. Things like that can change quickly.

    PE



 

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