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Article: Borax Project

  1. #1
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    Borax Project

    My Borax Project
    Borax is useful in many ways. Some of us worry about the purity of the commonly and cheaply available 20 Mule Team Borax. There is another concern in cases where accuracy of weight is important. Borax has 2 possible states of hydration, decahydrate and pentahydrate. If a 100 gram sample of pure borax has pentahydrate and decahydrate mixed, the assay will show a greater weight than 100 grams. If 5 grams of a 100 gram sample are the pentahydrate and the rest the decahydrate, no matter how purely the saple is composed only of sodium tetraborate and water of hydration, the assay will show 101.5 grams of the decahydrate. There is no way you can tell at time of collecting a sample from a large batch of pure mixture how much of each hydrate you are getting.
    A common solution to both problems is literally a solution. A saturated solution of borax at a given temperature contains a known weight of borax expressed as the decahydrate, whether the solid used to make the solution was penta- or decahydrate. If the solution was made saturated and separated from the solid at a low temperature, it will have a constant weight of borax per unit weight of solution at any (reasonable) higher temperature. The weight per unit volume will stay constant enough for most uses.
    A simple way to purify a large quantity of borax at the expense of a smaller amount is to make a concentrated solution in boiling water, allow it to crystallize at a temperature below that desirable for keeping, and decant the clear liquid and discard it or use it for cleaning. The soluble impurities in the original borax are presumed to be uniformly distributed in the liquid, so that if, say, 90% of the liquid is removable by decantation and/or fitering, the remaining impurities will be reduced by 90%.
    656 grams of borax decahydrate are soluble in a liter of solution at 100 C. If the temperature is reduced to, say, 15 C, there will remain only 37.9 gram in the discarded solution. The remaining 618 grams of borax has been cleansed of about 90% of its original soluble impurities and is sufficient to make 16 liters of borax solution.
    When I first proposed this approach it was considered by certain of our resident chemists to be a complicated alternative to paying the money for analytical reagent grade of borax and weighing it to the milligram, even though it is well known among other chemists and for the same reason I stated above that such a degree of precision is not warranted by the uncertainty of the state of hydration of borax. Then, to top it off, I had a senior moment and recommended the use of 10 times more of my borax solution than was proper for D-76. That was seen as proof that I knew not whereof I spoke. Furthermore I made the assertion that 10 times too much borax was not as bad as it might seem. In the process of defending my assertion, I found a variation of D-76 that I may (or may not) call "serendipitol". Serendipity is exemplified by the fellow who accidentally walked barefoot through a certain kind of animal excrement and discovered it to be an excellent cure of athlete's foot. I seem to remember that the animal was of the male bovine type.
    I made 3 liters of D-76, two with 10 times the prescribed amount of borax in the form of 425 ml of a 4.71% solution. To one of these were added 20 grams of boric acid crystals. The third liter was made as old-fashioned D-76, using 42.5 ml of the 4.71% borax solution. The rule of this game was to pretend I didn't know about the extra borax and treat it the same as store-bought. I shot 36 exposures of HP5+, bracketing plus and minus 1/2 stop. Any consecutive 4 frames had all three exposures. As it turned out, the nominal exposure was quite good in all three cases.
    I have three cases to show. Each one shows a low resolution scan of an 8x10 print to show its chiaroscuro and a high resolution scan of a portion of that print to show resolution and granularity. The one labeled "D-76" is Metol, 2 grams, hydroquinone,5 grams, 42.5 ml of 4.7 % purified borax solution, and demineralized water to make 1 liter. "D-76 B+" is Gadget's mistake with 425 ml of the borax solution. As cure of the resulting high contrast, I took a cue from more recent D-76 and added 20 grams of boric acid crystals per liter of the mistake and called it "D-76 BB". I used VC paper. I had the contrast turned all the way down for the D-76 B+ negative and no filtration for the other two. I set printing exposure for each print to make the whitest part of the fuzzy stuff in front of my great granddaughter's teddy bear the same.
    I got the expected high contrast from Gadget's Mistake, but grain and resolution were not seriously affected. Adding boric acid to make D-76 BB brought contrast back to near normal.
    Would there be a technical reason for making D-76 BB? Its pH is lower initially than that of traditional D-76 but its activity is nearly the same, at least on short strips. Its buffering capacity should be greater, both locally and overall, which should make a difference in the effect that different types of agitation make on gradations, but the effect may not be what one is looking for. In any case, it is another possible pictorial control.
    Gadget Gainer

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    Quote Originally Posted by Murray Kelly View Post
    And presumably glycerol doesn't affect the buffering ability of borax like glycol?
    At 1:50 my scratchings on an envelope indicate there's 5g Borax - 0.4g Phenidone - 0.4g AA per litre (working). My maths has been known to err in the past but is there a decimal place wrong in there?
    Long ago I made up some PC-glycerol and it appears to keep just fine. I had no glycol.
    Murray
    I don't know. If you made a solution in water with 5g Borax - 0.4g Phenidone - 0.4g AA I think you would find the usual 9.5 or so borax pH. This working solution is much lower, and the only reason I can see for it is the glycerol. I'm working on a second batch with much less heating. I'll let you know.
    Gadget Gainer

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    Quote Originally Posted by gainer View Post
    Here is an interesting fact. 526 grams of borax decahydrate will dissolve in a liter of glycerol. I dissolved 120 grams in 500 ml, added 10 grams each of Phenidone and ascorbic acid, used 1+50 dilution of this solution to develop Arista Premium 400 for 16 minutes at 70F with excellent results. I think this might be a good stand developer. The pH of the working solution was about 8.5. The borax brings with it the water of crystallization, but at most that would amount to about 56 grams of water. If you have time for such frivolities, it's fun to play with. Even with heat it seems it will not all dissolve, but give it some time.
    Is it a stable solution?..Evan Clarke

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    Quote Originally Posted by eclarke View Post
    Is it a stable solution?..Evan Clarke
    Seems to be quite stable once it all dissolves. The first batch has been sitting at room temp for a few days with no settling or discoloration. Even diluted 1+25 it's quite slow. I'm about to go to my chamber of horrors to try some more stand development.
    Gadget Gainer

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    I have learned that there is a glycerol borate. This is probably (I'm guesing, of course) what causes the sudden apparent change in solubility of borax in glycol as temperature reaches a certain point. The glycerol is no longer just a solvent. Is that good or bad or indifferent? Its formula is (C3H5BO3)n.
    Gadget Gainer

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    I am enjoying this and will try some of this but my interest is that I have a couple friends who are just dabbling in homebrew and want to make D76 but don't have good stirring capability. A water solution probably isn't consistent enough for them but this might be the ticket. I could just make them each a half liter of glycerol/borax. What's the pH of the glycerol/borax?..Thanks..Evan Clarke

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    If you can stir a teaspoon of sugar into a cup of tea (the kind you drink) you have all the stirring capability you need to mke D-76. Now for the chemicals, assuming you have a scale or balance:

    add 2 grams of Metol to a cup of water. It will dissolve right away. In a separate container, mix 5 grams of hydroquinone with 25 grams of sodium sulfite in a cup of water. Add this solution to the first in a container large nough to hold a liter. Bring the volume to 750 ml with water. Add 75 grams of sodium sulfite and 2 grams of borax and stir with a stainless steel or plastic spoon until it dissolves. Add water to make 1 liter. Voila! D-76 home brewed!
    Gadget Gainer

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    Maybe that will help them, I have good heated stirring equipment and just mix it in order and have no problems and like some other developers better. I will pass this routine on to them, thanks..Evan Clarke

  9. #58
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    Stand developed 30 minutes.

    The attached photo is a scan from an 11 power photo print of a negative stand developed for 30 minutes in 1+25 dilution.
    Attached Thumbnails Attached Thumbnails PCB-GLYCEROL-ST30.jpg  
    Last edited by gainer; 07-08-2009 at 09:43 PM. Click to view previous post history. Reason: No photo.
    Gadget Gainer

  10. #59

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    Quote Originally Posted by gainer View Post
    Here is an interesting fact. 526 grams of borax decahydrate will dissolve in a liter of glycerol.
    I think if you imagine glycerol as a chain of 3 carbon atoms linked together, with each carbon atom having one hydroxide group connected them you can see why.

    The hydroxyl groups are hydrophyllic - that's what accounts for the solubility in water of glycerine and for its hygroscopic nature. I suspect it's also what's responsible for its ability to dissolve numerous inorganic salts. It's kind of like having a molecule that's half water, and half organics.

    Quote Originally Posted by gainer View Post
    It turns out that the high solubility of borax in glycol is accompanied by formation of boronate esters that will be completely useless as bases. This is most likely to happen when heat is used to hasten solution.
    My understanding is that you will not make esters of borax this way, it merely makes a glycerol-borax complex. To make an ester, you'll need to drive off the water to push the reaction along. That means lots of heat - pretty much to the point of boiling. About 240°-280° C - now that's hot! And then at that point, you've made an glycerol boriborate ester, which will be useless for your purposes.

    Quote Originally Posted by gainer View Post
    I have learned that there is a glycerol borate. This is probably (I'm guesing, of course) what causes the sudden apparent change in solubility of borax in glycol as temperature reaches a certain point. The glycerol is no longer just a solvent. Is that good or bad or indifferent? Its formula is (C3H5BO3)n.
    OK - to make esters, you usually have to have an acid (often an organic acid), an alcohol, and a catalyst. For example, the esterification of acetic acid in excess ethanol (which also will act as the solvent for the reaction) will take place in the presence of concentrated sulfuric acid (the catalyst) and heat. This results in an ester, ethyl acetate.

    Quote Originally Posted by gainer View Post
    It explains why I thought my pH meter had gone bonkers.
    The reason you are getting lower than you expected pH values for borax dissolved in glycerol is that you are releasing boric acid when the glycerol-borax complex is formed.

    Glycerol forms a complex with the borax, forming monomeric or dimeric complexes with the glycerol. In borax, the sodium atoms are surrounded by borons atoms connected to other boron atoms with hydroxides bonded to the borons as well. The glycerol complex liberates som eof those boron atoms to form boric acid as it complexes. This free boric acid is what it lowering the pH of your solutions.

    In fact, I once used this reaction as the basis to determine the amount of boron (I was looking for borax) in an industrial product that I was hired to deconstruct - I think there was a bit of industrial espionage going on with that project... Anyway, you can titrate a solution of borax (which is basic) with sodium hydroxide (also basic), using pH 7 as the endpoint.

    Think about that for a second - you have a solution of borax with a pH of 10 or so, and you titrate it with sodium hydroxide with a pH of 13 or so - how do you get an endpoint of pH 7? (Isn't chemistry fun!?)

    The simple way is to add an excess of mannitol (a sugar alcohol with a structure rather similar to glycerol) or glycerol to react with the borax. The borax releases boric acid as a result of the excess glycerol or mannitol. (Neither glycerol or mannitol have much effect on the pH of the solution.) You add some methyl orange or phenolphthalein indicators and titrate to the endpoint of the indicator. The amount of sodium hydroxide used in the titration is proportional to the amount of boric acid liberated in the complexing reaction. You can then calculate how much borax was present in the original sample.

    I can list the chemical reaction equation if you like.

    So I'd say by dissolving borax into glycerine, you are liberating boric acid and consuming your borax. Probably not what you are really trying to accomplish by using the glycerol as a "solvent".
    Kirk

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

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    Quote Originally Posted by gainer View Post
    The onset of my interest in purifying borax was instigated by the assertion, made by PE and Kirk Keyes, that the 20 Mule Team borax from the supermarket is not pure enough for photo work, even though many of us have been doing so for years.
    To set the record straight, I suggested that 20 Mule Team may contain impurities that would interfere with photgraphic uses, and that photo-grade borax gives one some assurance that your reagents are suitable for photographic uses.
    Kirk

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



 

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