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  1. #31
    gainer's Avatar
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    "Therefore, they state that sulfite addition accelerates HQ and Metol development."
    I saw no such statement. I saw no place where they even implied such a statement. They did no tests that could be interpreted in that way. Those who produced the graph I sent did not present any evidence that HQ adds to the development by Metol, either synergistacally or simply. They did present evidence that sulfite accelerates development by Metol without HQ. I see no place where these researchers stated that sulfite accelerates HQ and Metol development.

    The graph clearly shows that there is not even an additive let alone superadditive effect between Elon and hydroquinone without the presence of either a sulfite or ascorbic acid. The activity of Elon is approximately doubled by the addition of either sulfite or ascorbate.

    My own experiments, which anyone can repeat, show that either sulfite or ascorbate at the same molar concentration stimulate the same degree of superadditivity between Metol and HQ, and at the same pH. The pH of a 10 g/l borax solution is bountifully sufficient for either an MQS or an MQC developer. The molar concentration of S need only be the same as that of the C. If you do not want stain, you can substitute as much sodium ascorbate as you want for the Q.

    At any rate, I learned what I set out to learn. Ascorbic acid, which is soluble in glycol or TEA, can be substituted for sulfite in such developers as the Pyrocat series and also in PMK in quite small amounts. There is no loss of activity if, OTH, sodium ascorbate is substituted for hydroquinone in the usual MQ or PQ developers.


    I doubt that Kodak had much interest in creating or promoting staining developers in glycol solution.
    Gadget Gainer

  2. #32
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    Patrick, the comment I reference is at the bottom of Page 366, right column which describes the experiment in figure 16.21 in detail. "oxidation products.... retard development" and then "activity returned by addition of sodium sulfte".

    This is the problem with a non chemist reading an argument on chemical reactions. This is A + B = C where C buildup retards development.

    If C has nowhere to go the reaction can virtually cease, but if C + D = something else, the reaction speeds up.

    Now, lets write Silver halide + HQ = Quinone + Silver metal. Silver metal is a solid, but quinone is in solution and blocks up the furhther reaction of HQ, all by itself or by making Quinhydrone.

    If you have Q + sulfite = HQ monosulfonate, then the reaction speeds back up again. QED.

    PE

  3. #33
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    The problem I have is that your QED doesn't follow from the experiment, however true it may be in general. The speeding up shown on the graph is of Metol without hydroquinone. Metol with hydroquinone but without sulfite shows no speeding up. Metol with either sulfite or ascorbic acid shows speeding up due to the formation of a Metol sulfonate by sulfite or to the reduction of the oxidized form back to Metol. Hydroquinone was not present at the same time as either sulfite or ascorbic acid. Therefore, any speeding up of the development in these experiments could not have come from formation of hydroquinine monosulfonate. I quote from the conclusion drawn from the experiment. "This evidence clearly suggests that the oxidized form of Metol retards development, in contrast to the behavior observed with hydroquinone." On page 366 you see the evidence that the oxidation products of hydroquinone clearly accelerate development and that the addition of sulfite retards development by the hydroquinone solution.

    I would have been a chemist if I had not switched from chemical engineering to aeronautical after three years. Beside, logic is the same for all who learn to use it. Logically, you should have seen that the experiment dealt with only the one agent. The usually quoted theory that hydroquinone regenerates the Metol in MQ synergism does not apply unless sulfite or ascorbate is present. It certainly does not apply when hydroquinone is not present.
    Gadget Gainer

  4. #34
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    The experiment on the precending page plus the other data show that the oxidation product of metol inhibits further development. Cross oxidation to remove the oxidation product of Metol speeds up the reaction. Either sulfite or ascorbate can act in this capacity.

    This is stated clearly in that paragraph. (At least to a chemist). Sorry Patrick, but that is my professional read on it. You are misinterpreting the data.

    PE

  5. #35
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    Maybe I didn't make my interpretation clear. Your statements until this one have implied that hydroquinone's reaction products are what make the MQ synergism work. The experiment in question does not investigate that synergism in the presence of sulfite. In fact, hydroquinone has practically no reaction at pH 8.7. What reaction it has at high pH is accelerated by its own reaction products when sulfite is not present. Addition of sulfite retards development by hydroquinone. OTH, Metol is capable of development without sulfite, but development is retarded by its own reaction products. The explanation for the accelerating effect of sulfite added to a Metol developer was the formation of a Metol sulfonate, not a hydroquinone monosulfonate. Ascorbic acid had the same effect, mole for mole, but by a different mechanism. Hydroquinone, I repeat, had no bearing on the experiments because it was not present in any test where sulfite or ascorbate was present. If hydroquinone had been present, the results could not hav unequivocally supported the conclusion that was drawn, that the reaction products of Metol, in contrast to hydroquinone, retarded development by Metol.

    Why are we arguing about these facts? How did I misinterpret the data? What difference does it make if I did? I got a working hypothesis out of it that did work as expected.

    All I can say is I'm glad you are not my physician. If you don't take this personally, I won't take your slurs on my logical thinking personally. You are the first person, other than my own father, who ever accused me of not thinking straight. I was about 6 years old at the time, and he was a Professor at St.Louis University. A close friend of his, and my sponsor at Confirmation, was Dr. Vernon J, Bourke, a noted Thomistic Philosopher.
    Gadget Gainer

  6. #36
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    Sorry about that. I think you think I'm trying to theorize about synergism. (We used that term at NASA as applied to human endeavors. Sometimes two persons can do more work together than the sum of what the two can do seperately.) All I wanted to know at first was whether it was reasonable to expect ascorbic acid to do the same job of promoting synergism between developing agents. The graph I sent did not satisfy me because it only dealt with one agent, considering that ascorbate is not much of an agent at pH 8.7
    but neither is hydroquinone. I have the answer. Thanks.
    Gadget Gainer

  7. #37

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    This discussion certainly makes me want to test a few of these compounds in my current developer. Photographer's Formulary sells Urea; any suggestion as to what amount to add to a liter of film developer as a start? They also sell ethylene diamine; here again any suggestions about starting quantity, and what effect on the film one might expect?

  8. #38
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    Patrick, your observations about the reaction are correct. The interpretation of the data is due to Kinetics and the nature of chemical equillibria, no more.

    Sulfite is NOT the cause of the synergism between HQ and Metol. As M&J says in the text, the rection of each is accelerated (they specifically refer to a Metol experiment as their major talking point).

    So, the bottom line is that what you say will work, but the reasoning is different to a chemist as to why. Thats all. Sorry if my comments seemed otherwise to yours.

    Superadditivity is an older word for synergy in some cases. It is still used in the MQ case.

    John;

    Urea is hit and miss. Remember, it softens film so be careful. I would start at 1 g/l and go as high as perhaps 20. Remember that it can cause reticulation. Ethylendiamine sulfate will cause fog if misused. I would use no more than about 10 g/l and that is it. It will change the pH too, IIRC.

    I am only bringing this up for experimenters to tinker with, so I'll have to say good luck. It is a chancy thing with both and that is why they are not used in production chemistry AFAIK.

    PE

  9. #39

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    Quote Originally Posted by Photo Engineer View Post
    Patrick;

    Sulfite also drags the oxidation of HQ to the right by scavenging the quinone by generating HQ monosulfonate which itself is a weak developer.

    But, as a number of people have said, the use of more than two developing agents is a real reach. I know that Haist has said that, and probably Henn and Lee as well.

    BTW, I have also made mention elsewhere of ETA developers. They are distinguished from superadditive developer combinations by having the pH adjusted to be optimum for the primary developer. The primary developer is present at very low concentrations. The other developer is not really active under these conditions except to regenerate the primary developer. These are unique and AFAIK there are not currently on the market.

    PE
    I am a chemist by training, though not an expert in photographic chemistry. However, I was reading about properties of developers one day and it occurred to me that an ascorbate/para aminophenol developer adjusted to pH 9 or so should activate the para aminophenol (perhaps weakly) but not the ascorbate, and that the ascorbate should regenerate the para aminophenol under these conditions. Does this sound something like what you are describing?

    One more thing. I understand that when ascorbate is oxidized it increases the acidity of the solution. If so would a developer such as I outlined above have a compensating effect by lowering the local pH in the gel in the areas of most active development, thereby inhibiting development in those areas?

    Alan

  10. #40
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    It certainly appears to work with phenidone and ascorbate in PC-TEA. At 1+50 dilution there will be almost 20 ml of TEA, which is about 17.8 grams, in a liter of working solution. There will be about 1.8 grams of ascorbic acid, which can make some kind of salt with about 1.5 grams of the TEA. With the 99% grade of TEA, the chart in the Dow Chemical manual for ethanolamines shows a pH of about 8.8 for the working solution. I have ordered some pH test strips that should help me be a little more specific as to pH in a week or so. This working solution is as active as D-23 full strength. P-aminophenol may require somewhat higher pH, but it should be in the range provided by some amount of borax. P-aminophenol and ascorbic acid are both soluble in propylene glycol or TEA. Higher pH could be obtained by using diethanolamine, but I have not tried it.

    In experiments I did today, the results from HP5+ developed in PC-TEA for 8 minutes at 70 F are no more grainy than those from D-23 full strength. This is hard to show in scanned images. There, the only difference I can see is a slightly greater sharpness in fine detail in the PC-TEA, but file size limitations here would make that hard to present.
    Gadget Gainer

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