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.
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
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!
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
The attached photo is a scan from an 11 power photo print of a negative stand developed for 30 minutes in 1+25 dilution.
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.
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".