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Thread: Chemistry

  1. #61
    b.e.wilson's Avatar
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    Don't bother. Umas hypothesis is wrong. CO2 does not, and cannot increase the pH of any solution into which it is dissolved; it can only decrease the pH of a solution if it is greater than 5.6 (carbonic acid is formed when carbon dioxide dissolves in water).

    I don't know what is meant by oxidation: is CO2 supposed to oxidize something, or is it oxidized? I'm certain CO2 is already as oxidized as it can be, but have no idea what might be in a developer/fix that would be oxidized by an oxidant as weak as CO2.

    As for the test, if your fix has a pH less than 5.6, then CO2 should work nicely as a protectant. For most developers it will lower the pH and render them unusable.

  2. #62
    Flotsam's Avatar
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    What Luck!
    I just ran across a mini bonanza of 4 long forgotten cans of Beseler XDL. I must have bought them long ago when it was becoming hard to find. I've been happily using Butane since reading the discussion here.
    That is called grain. It is supposed to be there.
    =Neal W.=

  3. #63
    Shmoo's Avatar
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    At one point in time, I posed the question of using "Private Preserve" on photo chemicals to the company. The response from Scott Farmer at PP was as follows:

    "Good Morning!

    Our photographer here in the Napa Valley (Robert M. Bruno Photography)
    has used our product for about 17 years in his darkroom. The only
    molecules in our can are inert nitrogen, carbon dioxide and argon...

    You should always start with fresh bottles, as nothing will reverse the
    oxidation process.

    Regards,
    Scott Farmer

    ps- We have had wine opened, and preserved with "PP" for as long as 4 1/2
    years."

  4. #64
    Flotsam's Avatar
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    Thanks Shmoo,
    Long ago, in another thread I wondered about using products that are meant to displace air in wine bottles for photo chems. It apears that the only consideration might possibly be expense.
    That is called grain. It is supposed to be there.
    =Neal W.=

  5. #65
    b.e.wilson's Avatar
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    Quote Originally Posted by Flotsam
    Thanks Shmoo,
    Long ago, in another thread I wondered about using products that are meant to displace air in wine bottles for photo chems. It apears that the only consideration might possibly be expense.
    ...and pH.

    I've said it before in this thread, but it doesn't seem to be taking, so here's the acid-base chemistry of carbon dioxide:

    CO2 dissolves in water to form carbonic acid (CO2 + H2O = H2CO3).

    Carbonic acid reacts with any base to neutralize the base if the pH of the solution is higher (more basic than) 5.6, which it is for most developers.

    Once the neutralization has happened, the concentration of carbonic acid drops, so more CO2 dissolves, neutralizing more base, lowering the carbonic acid concentration, so more CO2 dissolves.

    This process continues until one of two things happens: either all the base is neutralized and the pH of the solution is 5.6 or lower, or you run out of CO2 gas above the solution. The latter is more likely, since there are fewer molecules in a gas than in solution.

    So, during the dissolving/neutralization cycle, the pressure of the gas over the solution is dropping. What happens when it drops below the ambient pressure? Any leak will inspire air, thus oxygen. In the end you have only delayed the problem you have when storing a developer with air: the oxygen in the trapped air reacts with the develper, leaving a vacuum over the solution that will then draw in more air.

    If you want to preserve a developer (and what else would you want to preserve?) don't use CO2. With the exception, as I've mentioned, of ascorbic acid; it isn't a basic solution and won't react with carbonic acid.

    Concerning the statement by the wine protectant company, I can make only two things of it: either it's a lie, or the amount on CO2 is so low that it has no effect on the solution pH. I'd like to believe tha latter.

  6. #66
    dr bob's Avatar
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    Quote Originally Posted by b.e.wilson
    ...and pH.
    > lot of cutting here<
    Concerning the statement by the wine protectant company, I can make only two things of it: either it's a lie, or the amount on CO2 is so low that it has no effect on the solution pH. I'd like to believe tha latter.
    I believe you have it correct. We use a similar technique and material(s) in removing CO2 from submarine atmosphere. As far as the wine industry: my memory (such as it is) says that CO2 is a natural by-product of fermentation. I know that my wine making apparatus used a water seal (bubble) to vent the gas. You can tell when the reaction is “complete” when the bubbles slow down. So I guess that industrial wine comes out pretty much saturated with CO2 so a little added to the void area wouldn’t hurt.

    Agree: using CO2 around developer(s) is NOT recommended.
    I love the smell of fixer in the morning. It smells like...creativity!
    Truly, dr bob.

  7. #67
    Jorge Oliveira's Avatar
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    Quote Originally Posted by b.e.wilson
    Carbon dioxide will react with a basic solution (which most developers are) very quicky to neutralize it. Avoid CO2 at all costs. It will react and leave a negative pressure in the bottle, which will suck air in.

    Might be OK for ascorbic acid developers, though.
    Ascorbic acid devs (Xtol and the like) are alkaline, as any other devs.
    Could you pls elaborate on why would it be Ok to use CO2 with them?

    Thanks,

    Jorge O
    Curitiba - nice place to live, if you don't care about the weather...

  8. #68
    Flotsam's Avatar
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    Thanks to the informed discussion here this has been a very a helpful thread.
    I was not educated enough to understand why using inert gas to displace air in a wine bottle would differ from doing the same thing in a developer bottle. The discussion of CO2 has been fascinating.

    Thanks to all who took the time to contribute.
    That is called grain. It is supposed to be there.
    =Neal W.=

  9. #69
    b.e.wilson's Avatar
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    Quote Originally Posted by Jorge Oliveira
    Ascorbic acid devs (Xtol and the like) are alkaline, as any other devs.
    Could you pls elaborate on why would it be Ok to use CO2 with them?

    Thanks,

    Jorge O
    Being a color man, I haven't used ascorbic acid developers, and wasn't aware they were alkaline.

    CO2 will lower the pH, then.

  10. #70
    jnanian's Avatar
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    ed -

    you can probably get argon at a place that sells welding gas - the same places that sell tanks of helium. you could also find a sign company that does neon & cold cathode work. argon, one of the non-reactive "noble gases" ( its outer shell of electrons is full so it will not react with anything else ) is used like neon & other gases and sometimes phosphors to make colored lighted signs. neon (gas) without any phosphor additives has the characteristic color of red and the sign makers usually add a tiny bit of argon to it to make it electrify brighter. argon can also be used alone like neon (gas) and it has a characteristic color of blue.

    http://www.sign-makers.com/listings/USA/MA.html
    has a listing of sign-a-rama and they are in danvers & tewksbury ... if you are still looking for a tank of argon, you might give them a call

    good luck!
    john

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