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  1. #1
    Ian Grant's Avatar
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    Modern Rodinal Substitutes Part II

    Apologies for having to start a new thread but I can't read or even access the first to reply to posts.

    So with a bit of telepathy

    Quote Originally Posted by Kirk Keyes View Post
    Well, there's a problem there, as it's really hard to measure pH accurately when it gets much above 12.5 or so. You have to start getting special electrodes and the like.

    But for MSDS work, it doesn't have to be too precise.
    __________________
    Kirk

    A point that's being missed is that A&O give a figure of 2.7% Potassium Hydroxide not 3% in older Agfa MSDS.

    The pH is around 14 sure, but the actual requirement is the pH of the working dilute solution rather than the concentrate which is given elsewhere as pH 11.55, which I commented on in the first post of the thread.

    Way back Ron (PE) mentioned adjustments to Rodinal before bottling, the question we need to ask is are they adjusting on the basis of the concentrate, or also doing some tests on a dilute sample, as this will be a far more accurate indicator.

    Can someone please post a link to this continuation on the original post.

    Ian

  2. #131

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    Quote Originally Posted by Kirk Keyes View Post
    Ray - if you've been following along for the last couple years, you would have remembered that pX is useless when there is a mixture of halides in the system. What does that number tell you when there's a mixture?

    Thus, pAg is measured instead.
    Yes.
    pX is used only as a placeholder...
    It indcates only that we could be talking about any halogen,
    even mixtures.

  3. #132
    Photo Engineer's Avatar
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    Kirk;

    Regardless of the halide ratio, the absolute Ag+ in solution is the item of concern. With that in mind, pAg or vAg then becomes the measure of choice. With mixed halides or between Cl/Br/I and mixtures thereof the pX can be just about anything, but equimolar Br and I for example alone will give nearly the same pX or vX, but the vAg or pAg may be different by a huge amount. Therefor it is easier to measure Ag+ with precision by use of the Silver ion in solution regardless of halide type or mix thereof. This then determines excess halide, of whatever type, in the coating at the start of the process, and also helps with keeping.

    Of course, I like to prewet which normalizes vAg to be about that supplied by city water which actually seems to do nothing with D-76 or HC-110. Now, I have to try Rodinal.

    PE

  4. #133
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    Quote Originally Posted by Photo Engineer View Post
    Patrick;

    I won't laugh, but one operation I will not do is filter a concentrated KOH solution. Too much chance of an accident, and the KOH usually ends up dissolving the filter paper. The CaCO3 is colloidal and can go through the filter paper.

    Best use a sintered filter for this one, if it even works.

    PE
    Yes, some not only goes through the filter, but very soon clogs it so that not much of anything goes through. I don't try filrering any more. I stir vigorously, let it settle, and stir again. After it settles, I decant most of the clear liquid as slowly as possible so as not to stir up the settlement. It's not the best way to prepare a really concentrated KOH solution, but I think it will be good enough for Rodinal. A gram molecular weight each of Ca(OH)2 and K2CO3 will produce 112 grams of KOH . I don't need more than 30 grams, which should be easilly gotten if I use enough water to make a 30% solution. It's theoretically more wasteful than filtering, but the ingredients are not very expensive and can probably be more easilly bought in some places.
    Gadget Gainer

  5. #134
    gainer's Avatar
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    P.S.- Any thing that will filter my coffee will surely stand KOH.
    Gadget Gainer

  6. #135
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    Quote Originally Posted by Kirk Keyes View Post
    Have you collected some and done some spot tests to see what it is? Does it burn after drying? What's the pH if you dissolve it in some more water? If you can dissolve some in water, does it form a precipitate with calcium ions?

    There are 3 simple tests to get you headed in the right direction for identifying the precipitate.
    It does dissolve when I add more water.
    My tap water is eminently suited for drinking because of its good taste and calcium content. It forms a precipitate in most developers that contain carbonate. I don't see that with this version of Metolal, but I have been using demineralized water. If I were to substitute an equimolar amount of p-aminophenol and reduce KOH accordingly, I would see no lingering precipitate. I can try that as soon as my shipment of p-aminophenol arrives.
    I hate to try filtering the K2SO4 out of the precipitated metol freebase, but if everything else dissolved, that should tell me something. At the moment, I'm also fresh out of Metol.
    Gadget Gainer

  7. #136
    gainer's Avatar
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    Quote Originally Posted by Kirk Keyes View Post
    Looking at your photo, it looks like you have more than me!
    Some say I have the bulging forehead of a genius. Others say I have a receding hairline. The largest brain recorded is said to have belonged to an imbecile, the smallest to a genius.

    When I played the Baroque Oboe with the Governor's Palace Orchestra at Colonial Williamsburg I had the advantage of wearing a wig, so nobody could tell about anything but my music. The oboe has been described as "the ill wind that nobody does good."
    Gadget Gainer

  8. #137

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    Kirk,

    Somewhere, you described for Bill the calculation of pH of... (I think)
    a KOH solution.

    Do you know where it is?

    My searches are mute...

    Ray

  9. #138

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    Quote Originally Posted by gainer View Post
    The oboe has been described as "the ill wind that nobody does good."
    Just had to say that I LOVE that quote!!

    Following this thread with rapt interest - but nothing to add 'cos it's way over my head. Have a son whose just started his doctoral programme in Chem. Maybe he can explain (some of) it to me!!!


    Bob H
    "Why is there always a better way?"

  10. #139

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    Quote Originally Posted by Ray Rogers View Post
    Kirk,

    Somewhere, you described for Bill the calculation of pH of... (I think)
    a KOH solution.

    Do you know where it is?

    My searches are mute...

    Ray
    Ray - that's near the end of Part I of the original thread that spawned this thread. There's a link near the beginning of this thread that links to the first part. Then it's on the last page or two.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  11. #140

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    Quote Originally Posted by Kirk Keyes View Post
    Ray - that's near the end of Part I of the original thread that spawned this thread. There's a link near the beginning of this thread that links to the first part. Then it's on the last page or two.
    Thanks found it.
    Unfortunately, I replied there, somewhat akwardly too.
    It should have been here but I am confused with the two threads...

    Respond where ever seems most .....

    Ray



 

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