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  1. #1
    gainer's Avatar
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    Experiments with Metol and ascorbic acid.

    The factors affecting developer activity are temperature, pH,
    concentration, products of aerial oxidation, products of silver halide
    reduction, and the orientations of the heavenly bodies.
    According to some experimental results reported in "The Theory of the
    Photographic Process" as little as 0.05 moles (6.3 grams) of sodium sulfite in
    a liter of Metol developer will double the rate of development that is
    obtained when no sulfite is present, pH being held at 8.7 in both cases.
    It is explained that oxidation products of Metol restrain development, and
    that sulfite counteracts these products by forming the sulfonate.
    Ascorbic acid will do the same degree of acceleration without sulfite, also at pH 8.7. In this case the oxidized Metol is reduced back to its original form. The ascorbate is itself oxidized and pH is decreased in the process. The decrease in amount of active Metol in the one case or the decrease of pH in the other may not cause much difference in capacity and storage longevity between a Metol-sulfite and a metol-ascorbate developer. However, it would seem that a well buffered working solution might tip the balance in favor of the ascorbate.
    I will explore first a 0.05 molar concentration of Metol, which is
    approximately that of D-23, together with a 0.05 molar concentration of
    ascorbic acid. It remains to formulate the alkali needed to make the pH less
    than that at which an ascorbate becomes a developer and great enough to ensure activity of Metol.
    I calculate that 0.1 moles of sodium hydroxide will neutralize the 0.05
    moles of sulfuric acid attached to the Metol base plus the 0.05 moles of
    ascorbic acid, leaving 0.05 moles each of sodium sulfate and 4-(methyl-
    amino)phenol and 0.05 moles of sodium ascorbate. The net pH thus far is still
    not alkaline enough to develop film in a reasonable time, nor does it have the
    necessary buffering action to keep the pH from going lower yet. A few grams of borax should bring the pH up to about 9.2 but even 20 grams will have little
    more effect on pH and should give a cushion against reduction of pH during
    developing.

    The resulting recipe is:
    Metol.............8.5 g
    Ascorbic acid.....8.8 g
    Sodium hydroxide..4 g
    Borax.............20 g
    Water to 1 liter.

    The concentration of Metol is about 13% greater than in D-23 and the
    concentration of sodium sulfite is nil.
    The pH of this mixture, which I measure with test strips to be about 9, is
    below that at which the ascorbate is a developer of any consequence. The
    initial activity of the mixture is about that which could have been obtained
    with sulfite in place of the ascorbate, so it does not seem that synergism
    between Metol and ascorbate is the explanation.
    The ratio of borax to caustic in this formula is quite close to the
    effective ratio in sodium metaborate. 14.5 grams of sodium hydroxide and 69
    grams of borax in a liter make a solution that is often used as a substitute
    for 10% sodium metaborate. 276 ml of such a solution, or 27.6 grams of Kodalk if you prefer, will contain the equivalent of 4 grams of sodium hydroxide and about 20 grams of borax. It may be easier to get sodium metaborate than sodium hydroxide through the UPS. The recipe then becomes:
    Metol..............8.5 g
    Ascorbic acid......8.8 g
    Sodium metaborate..27.6 g or 276 ml of 10% sodium metaborate solution.
    Water to 1 liter.

    All ingredients are quickly dissolved in room temperature water. HP5+
    developed for 8 minutes at 68 F gives normal contrast, showing that the
    solution could be diluted. In fact, diluting with an equal part of water
    increased development time by only 25%, probably because the pH of this
    solution does not change much with dilution. 125 ml diluted with 125 ml of
    water did a 36 exposure roll of HP5+ to normal contrast in 10 minutes, which
    means of course that a liter of the above formula will do 16 standard rolls
    without reuse. As a matter of interest, twice the above recipe can be squeezed into one liter.
    By the way, don't be confused by the fact that there exist 4 mol and 8 mol
    metaborates. A gram of one has the same number of atoms of sodium, boron,
    oxygen and hydrogen as a gram of the other. At 53.6 C, without losing any
    water, Na2B2O4.8H2O becomes NaBO2.4H2O which is stable to 105 C. In other words, the distinction between 4 mol and 8 mol sodium metaborate is academic, not practical when we specify solution strength in terms of weight per unit volume. You may see this for yourself at www.borax.com.

    I am attaching a scan of a 10x print from FP4+ developed 8 minutes, 68 F. This is not of very high resolution, but may serve to illustrate gradations. I have also attached a higher resolution scan of a small part of the same print. If you print the high res. scan to 6x9 inches, you will see about a 50X magnification of that part. I have no idea how these will show up, but you can imagine that the originals are better.

    As it turned out, the attachments showed up at the end of the thread on superadditivity started by PE. My fault.
    Last edited by gainer; 06-03-2007 at 10:23 AM. Click to view previous post history.
    Gadget Gainer

  2. #61

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    Quote Originally Posted by gainer View Post
    The basic guidelines of Technical grade borax powder are well known,
    Well known? - didn't you just point out that there are two different specs for the same grade of borax? Granular and powder - both called Technical Grade, have differing specs?? That's pretty precise!

    Also, you say,
    Quote Originally Posted by gainer View Post
    Let me point out that the highest grades I have seen specified by Rio Tinto and others guarantee the sodium tetraborate decahydrate equivalent to be between 99.9 and 105 or even 110 %.
    That's not the highest grade that you have seen. Technical grade is usually considered the lowest grade. Surely you read the assay that Mick listed for the results of his ACS Analyzed Reagent Grade Borax - it listed "Assay = 99.101%". http://www.apug.org/forums/forum37/4...tml#post556946

    Let's think about that for a second to let it sink in... One grade has a precision of 5 digits, the other grade has a precision of 10%. Now which one should we consider to be the higher grade? I hope you answered this one by saying "AR Grade" to yourself.

  3. #62

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    Now if you are really determined to purify your own technical grade borax into the equivalent of reagent grade, then I would suggest incorporating the following suggestions:

    First, boil your solution. And do it for a while, like an hour. It does not have to be saturated while you boil it - that would be a pain as the solution would want to crystallize out as you are boiling it. And it doesn't have to be a hard boil, just keep it near boiling for the hour. The reason is that you want to try and use the high pH and temp of the boiling borax solution to hydrate any silicates in the borax. This will help them drop out of solution and make them easier to filter out.

    Second, filter your solution to remove insoluble matter. Get yourself a large (like a 20 or 30 cm diameter) Buchner funnel and some glass fiber filter paper. The Buchner funnel can readily be found on ebay for less than $20. Get a glass filber filter paper like Whatman GF/C which has a pore diameter of about 0.45 um. This will remove all particulate.

    Third, after you've done your leach to remove the chloride and other things that are more soluble than borax, use enough water to dissolve your remaining borax so that it makes a saturated solution at a temp of about 80 to 100F. This way, after you've boiled your borax solution, you can let it cool down some to make it safer to handle, and then filter it with the Buchner and a vacuum to help it pull through the filter. So filter it when it reaches about 125F and the borax will stay in solution and not clog the filter.

    So now you have a filtered solution of borax, with no insoluble solids. Since we dissolved enough borax into the liquid so that we would reach saturation at about 80F, we will get some crystals of borax precipitatating out of our solution when we get below 80F. Go ahead and cool it and hold the temp at your 63.6F. That's the hard part of your procedure - hitting that temp and holding the solution there until all the borax drops out of solution. Constant agitation from a magnetic stirrer would be good here. Let it sit at that temp for a significant period with the excess crystallized borax in the bottom of the container. When you think it's been long enough at 63.6F, then decant the solution into another bottle and store it at a temperature that is higher than 63.6F.

  4. #63
    gainer's Avatar
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    Chemically pure sodium tetraborate powder will assay as almost 200% chemically pure sodium tetraborate decahydrate because it can make that much decahydrate by absorbing water. You can look up the NF grade which has practically no soluble or insoluble impurities and you will find that as the decahydrate it will assay as between 99.9 and 110%. I don't know where you learned your chemical engineering, but I hope you didn't learn all they were teaching. Most reputable schools would be better than that.

    You will not precipitate any water insoluble solids from technical grade borax decahydrate powder.

    You are saying that if I don't filter my borax solution, it will have insoluble solids in it.
    Gadget Gainer

  5. #64
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    First, Virginia ham is cured with Sodium Nitrate and Sodium Nitrite, not with Borates! Again, chemicals are being mixed up and this mixup can cause a deadly accident if someone tries to make their own cured ham.

    Second, Patrick, I read your posts, you did not read mine. I said that you could concentrate impurities in BOTH the solid Borate that does not dissolve and in the saturated liquor.

    Kirk has described a sound laboratory method above. I described a scenario which you obviously did not read or understand in any way. It is a hypothetical case illustrative of what I'm saying to you.

    PE

  6. #65
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    Quote Originally Posted by Kirk Keyes View Post
    We all know where to find the specs. We just don't have a copy of it. Perhaps you do, Neanderman?
    Try a library. That citation came from the Illinois State Library on-line catalog. I live in Cincinnati, my public library has some of the ANSI/ISO standards.

    Ed

  7. #66
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    Quote Originally Posted by Photo Engineer View Post
    First, Virginia ham is cured with Sodium Nitrate and Sodium Nitrite, not with Borates! Again, chemicals are being mixed up and this mixup can cause a deadly accident if someone tries to make their own cured ham.

    Second, Patrick, I read your posts, you did not read mine. I said that you could concentrate impurities in BOTH the solid Borate that does not dissolve and in the saturated liquor.

    Kirk has described a sound laboratory method above. I described a scenario which you obviously did not read or understand in any way. It is a hypothetical case illustrative of what I'm saying to you.

    PE
    I didn't say Virginia ham, I said Smithfield Ham. If you've never seen one, there's no use trying to describe it. I wasn't talking about the particular substancesto be removed, but about the method of removing...washing, in essence.

    I know you can concentrate insoluble substances in the remaining solid and soluble substances in the saturated liquor. That is the purpose in making the liquor. When you dispose of the liquior, that disposes of most of the soluble impurity, leaving only that in the liquor adsorbed by the undissolved borax. When I make the SECOND batch of saturated liquor, It will have less soluble impurity than the first, in the example I provided, by a factor of at least 16.

    I have accomplished two things by this rather simple procedure: I have a solution with less soluble impurity than if it had been made by dissolving the raw borax, whatever grade it started as, and I know the weight percentage of borax decahydrate with a certainty greater than you know the weight percentage of the dry powder, no matter what its grade, for the simple reason that sodium tetraborate could be in any of three states of hydration in the powder, but only one in the saturated solution. You can buy the NF Powder grade, which has as its only impurity =<20 ppm heavy metals and you will see that the guaranteed percent of Borax Decahydrate is 99.0 to 105.0. That uncertainty is due to the uncertainty of the water content, not the borate. Thus, if I have a saturated solution whose weight percentage I know to be between 3.95 and 4.05, I know as much about my measure of borax decahydrate as you would by weighing the powder directly. The slope of the curve vs temperature in that vicinity is about 1.6 wpc/decree C. How do you know the water content of the batch of AR you got after you've had it a while?
    Gadget Gainer

  8. #67

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    Quote Originally Posted by Neanderman View Post
    Try a library.
    I've tried the local state university. Nothing. I guess I need an interlibrary loan.

  9. #68

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    Quote Originally Posted by gainer View Post
    I didn't say Virginia ham, I said Smithfield Ham.
    Pat, I'm a Yankee. I'm not familiar with one of these hams. It was too obscure of a reference. I see they are dry cured and need to be rehydrated so they are fit for human consumption.

    You said:
    Quote Originally Posted by gainer View Post
    Come to think of it, people in Virginia use it on Smithfield hams. The ham must be soaked in water for quite some time, the water removed and replaced by fresh, and the process repeated several times to get the salt to the point where a person can safely eat the ham. And you pay a lot for the privilege of doing it.
    Your statement is unclear in respect to the previous dicussion. It's really easy to assume you are talking about "it" being borax.

    When I make posts, I type them out as I would when speaking, and then I go back over them and reread them to look for where I can make them more clear and precise. I replace a lot of "it"s with the actual item name or decription so it reads more clearly.

    By the way, Borax was used as a "bug killer" in the production of hams beginning in the 1880s or so - it keeps the "skippers" out, some kind of fly that spoils ham. The FDA does not allow this use, as we all know and with your propensity for talking about borax as a home remedy, who can tell what you are talking about?!

  10. #69
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    Both Viginia and Smithfiled hams are salted and cured in the Sodium Nitrate/Nitrite solutions. They may or may not be dried, I don't remember which is and which is not. Prosciutto hams are made much the same way by salt curing and air drying with no other treatment.

    One type is soaked in water before cooking or is cooked in water that is discarded. The other can be eaten directly if properly cured and or smoked during the curing process. They may be 'cold' smoked or 'hot' smoked just as fish is often smoked both ways.

    As for your procedure with Borax, yes, it requires repeated recrystallizaations to work properly and does depend heavily on the types of impurities present, but I stress REPEATED recrystallizations as you stressed. One sequence will often not work and this is what you have to understand. This involves so much extra labor and uses so much water (as I said in previous posts) that the user is well advised to buy pure product to start with or the cost will soar.

    I think that this is going quite astray by trying to prove that lower quality materials can be used. They can work, but you can also pay a price in terms of quality that can bite you in many different ways as I have pointed out before.

    I should add that not knowing the starting purity of an impure substance often leads one to using an incorrect number of recrystallizations. I had to run purity tests after each recrystallization that I ran in graduate school to prove the purity before I sent it out for analysis to get the 'final' purity verified. We did much the same at Kodak.

    I remember one chemical that was so difficult to make and purify that they used the largest reactors to run it and ended up with a tiny bottle of photograde material at the end which was worth thousands of dollars, just to get the purity level needed. It was an ingredient that went into an emulsion.

    PE

  11. #70
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    I have to apologise for being unclear about what happened to the first batch of saturate. I thought I had said "Throw it out or use it for drain cleaner". As for rewriting, you shold have seen the first three versions.

    I know that you are doing things with home made emulsions that require much more precise measurements than does film development, where much of the time we do not know for sure what contrast we need in the negative, and in roll film, we must often strike an average and do the rest in printing. The use of borax, metaborate, carbonate qnd many other chemicals can often be done as a chef does his favorite recipes..a dash of this and a pinch of that. To my knowledge, I have never in over 65 years used borax where a measurement error of 5 or 10 % would make a noticable difference. As for the guaranteed limits of chloride, sulphate and iron in technical grade powdered borax, a fingerprint on a mixing utensil might have as much effect. I know for a fact that I cannot see enough diference from adding 50 grams of sodium chloride to a liter of D-23 to make it worthwhile, so I cannot see how 700 ppm in 2 grams of borax would do any damage, nor 600 ppm of sulphate when 2 grams of Metol carries more than that into a liter of working D-76. Insoluble particles are specified <400 ppm in granular tech grade but none in powder tech grade. I suspect the insoluble particles are sand, but who knows? If so, it's not one of those things a production line would want to grind to powder.
    Gadget Gainer



 

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