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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.
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    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. #111

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    Quote Originally Posted by gainer View Post
    If all dissolves, the solution will contain 28.8 grams K2SO4.
    Why is there 28.8 grams K2SO4 in there? I get 21.2 g by my calcs.
    The MW of metol is slightly less (172.19) vs that of K2SO4 (174.3), but there is only 1/2 mole of sulfate for every mole of metol free base, so you should get just a bit more than half of what you started with. Metol, the source of the sulfate ion, is the limiting reagent, and there is an excess of KOH.
    Last edited by Kirk Keyes; 09-02-2009 at 07:18 PM. Click to view previous post history. Reason: my calculator is on crack...
    Kirk

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

  3. #112

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    By the way, Cole-Parmer sells 45% w/w potassium hydroxide for $44 for a 1 L bottle. And that's AR grade, really pure stuff! That will have 655 grams KOH per liter. 500 g of ACS Certified KOH pellets (really pure in solid form) will cost you $76.

    It's worth buying it in liquid form in my book. And a lot safer...
    Kirk

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

  4. #113
    gainer's Avatar
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    The MW of Metol is listed as 344.39, which includes 1 MW of H2SO4, 98.08. I used 1/8 MW of Metol, so 0.125 MW H2SO4 went in and were neutralized by 0.25 MW of KOH leaving 0.125 MW of K2SO4 and some water. I calculate now 22.01 g K2SO4. I must have slipped a cog sometime about 2 AM. I'm close to you, but not for the same reasons. There are TWO molecules of the Metol base for each molecule of H2SO4, so each MW of Metol requires 4 MW of KOH to completely free two MW of the base, which is (344.39 - 98.08)/2 or 123.16. Since I'm using 1/8 MW of Metol, I need 28 g KOH.
    Gadget Gainer

  5. #114

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    Quote Originally Posted by gainer View Post
    There are TWO molecules of the Metol base for each molecule of H2SO4
    Ha! There's one half sulfuric acid molecule complexed with every N-methyl-p-aminophenol! :^)

    By the way, 41.8/344.38= 0.121 moles, and not 0.125 moles. So you don't actually have a full 1/8th mole.

    Even then, 0.125 moles of K2SO4 (MW = 174.26) should equal 21.78 grams.

    But we're splitting hairs.
    Kirk

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

  6. #115
    gainer's Avatar
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    I wasn't splitting my hair. I just used the round numbers for most of them. I can't afford to lose too many hairs.
    Gadget Gainer

  7. #116

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    Quote Originally Posted by gainer View Post
    I wasted a lot of time trying to dissolve it by bringing the pH up to 14.5 (stupid meter didn't know any better).
    I think I mentioned earlier in this thread or in Part I that pH meters just are not up to measuring above about pH 12.5 unless you have special electrodes and suitable standards. You should really take any pH meter reading above that level with a really big grain of salt unless you konw what you are doing and have the right equipment...

    By the way, why not stop at pH 14?
    Last edited by Kirk Keyes; 09-03-2009 at 01:24 AM. Click to view previous post history.
    Kirk

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

  8. #117

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    Quote Originally Posted by gainer View Post
    I wasn't splitting my hair. I just used the round numbers for most of them. I can't afford to lose too many hairs.
    Looking at your photo, it looks like you have more than me!
    Kirk

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

  9. #118

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    Quote Originally Posted by gainer View Post
    In any case, something is not all dissolving that I thought ought to.
    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.
    Kirk

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

  10. #119
    Photo Engineer's Avatar
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    Many pH meters come with an electrode correction table for temperature and pH values that deviate too far from the norm. I used to use that when I made up high pH solutions or when I ran processes above 75F.

    PE

  11. #120
    Photo Engineer's Avatar
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    An important note regarding old and new emulsion types has been bothering me regarding the evolution of the Rodinal developers and several other formulations.

    Old style emulsions were washed to a given conductivity, and this was done after the treatment with sulfur. Later emulsions were still washed to a given conductivity, but some had sulfur + gold added, the sulfur being in the form of thiocyanate.

    Modern formulas are untreated with sulfur, washed to a given vAg, treated to balance the final salt content at a fixed figure, and then sulfur + gold finished in a manner in which the sulfur may be in the form of some quite exotic compounds. They are then surface treated for spectral sensitivity with some dyes quite different than those used 50 years ago and are treated with agents to preserve the emulsion that are quite different than the early chemistry.

    So, today's emulsions are vastly different in precipitation but also in workup prior to coating, and in such a way that the silver solubility is quite different.

    Just some thoughts from someone who has worked on each side of the silver curtain.

    PE
    Last edited by Photo Engineer; 09-03-2009 at 12:51 PM. Click to view previous post history. Reason: changed developers to emulsions as pointed out.



 

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