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
Originally Posted by Kirk Keyes
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.
BTW, Guys going through all this posts, I also tried to mix some Rodinal.
I used this recipe:
potassium metabisulfite 150g
Sodium hydroxide 100g
Potassium Bromide 5g
Sodium benzenesulfonate 0.3g
This recipe comes from Soviet Union the most known book, and states this as Foma R09 Rodinal recipe. The only difference - the formula asks for p-aminophenol hydrochloride or hydrosulfate), but looking at your discussion this is definitely the mistake. It must be the base.
The principle is almost the same as usual - slowly add Sol B into Sol A, until precipitate almost dissolved.
The add Sol C, and water to make 1l.
Sodium benzenesolfonate is used to prevent oxigen diffusion into the solution. Greatly extends it life. Has no effect on the developer.
Looks it is very similar in it's activity and properties to Agfa modern Rodinal, what is different - the color, it is very light when fresh.
Of course pH goes up like that. But you're entirely missing the point.
Right from day one when Agfa began making Rodinal (until the major shift in 1964) the important part of manufacture of it or the substitutes was that there was just enough Hydroxide to convert the metabisulphite into Sulphite and react with the p-Aminophenol. See the 1910 "Agfa" Book & remember who wrote Agfa's German handbooks - Dr Momme Andresen, who discovered p-Aminophol and designed Rodinal. To quote "Agfa-Rodinal contains only an alkaline salt of Paramidophenol, but no excess of caustic alkali". Later when they manufactured with Potassium Sulphite the level of Hydroxide dropped substantially as would be expected due to the reactions taking place.
Whether there's a trace of excess Hydroxide in Calbe R09 or not is immaterial what's important is that the bulk of the hydroxide has reacted to form that "alkaline salt of p-Aminophenol, that itself will increase the pH.
What's certain is that the pH is significantly lower than it should be from the amount of Hydroxide in the formula.
Yes your right it's the same basic Andresen formula, I THINK there's not enough Hydroxide though to convert all the Metabisuphite into Sulphite, I'd have to go back & find the calculations which I have somewhere. If not all the Metabisulpte is converted it'll have far better keeping properties as there will definitely be no free Hydroxide.
It's the fact that there's the Sodium benzenesulfonate is used that's interesting and needs checking out.
Originally Posted by pavelt2tk0
Correct me if I'm wrong, but I seem to remember learning that pH=14 does not necessarilly mean that the solvent that is causing that pH is saturated. In the case of strong alkalis, pH=14 may occur far below saturation, but cannot increase as more alkali is added. An acid-base reaction may occur in a strong solution of KOH and go to completion, leaving the pH at 14, with capacity remaining for more such reactions.
What happens to pH when we add just enough KOH to an amount of paraminophenol to form the potassium paraminophenolate? It seems to me that pH>7 implies that more than enough KOH was added, but even pH=14 does not tell us how much more.
Sponsored Ad. (Subscribers to APUG have the option to remove this ad.)
What is certain is that KOH + pAPH = KpAP + HOH which is a neutralization.
But, KpAP + HOH is an equillibrium reforming KOH + pAPH which is present as K + OH. Also, if you look at the molar equivalents used above, 100 g of NaOH in this case is over 2 moles of hydroxide and less than 1 mole of pAP. Even if it were the sulfate the pAP would be overwhelmed by the caustic. The Metabisulfite contributes little to this reaction in terms of OH, merely introducing the SO3= ion.
As a result, regardless of what is said, if the pH is above 7, the solution is alkaline and contains OH ions. This is fundamental chemistry. If it were acidic, then there would be H+ ions. At 7.0, there would be equal numbers of H+ and OH-. Thats fundamentally just water. That is the only place on the pH scale where there is no excess of acid or base, and that is called neutrality.
The caustic may even be equimolar to pAP or its salt, but the equillibrium causes an excess of OH- to form in the solution and that is a chemical fact. That is why the pH is so high, due to an excess of OH-. Dr Andresen may have been in error or trying to mislead people, IDK, but his statement is certainly misleading in the face of the formulas and pH values I have seen.
Originally Posted by gainer
You are quite right. It also tells us though that an alkaline solution has so many moles / liter of hydroxide ion present.
Spot on Patrick, you understand what I'm getting at.
Originally Posted by gainer
It's the fact that the "potassium paraminophenolate" in a high concentration Potassium Sulphite solution has a pH of around 11.8 and when we have excess of hydroxide as in the more modern Rodinal formula we go to pH 14
pH 14 is in fact listed as being reached by 5.6% KOH solution, the MSDS's for A&O Rodinal show the KOH is only 2.7%. But 0.5% KOH is pH 13 and the Sulphite is pH 9-10 anyway so every thing there seems as expected.
When you say that Potassium Sulfite solution is alkaline, what you are really saying though is that there is an excess of OH- created when you add Potassium Sulfite to water. Again, the alkalinity comes from the equillibrium which causes OH- to break off from water and form an excess of hydroxide (or alkali) and thus, KOH is present in solutions of Potassium Sulfite.
BTW, I have no electronic pH meter, but used indicator paper, it shows pH about 11,5-12.
Originally Posted by Ian Grant
And the thing - I just took the bottle of original Agfa Rodinal (produced 2006-2007) - it has large (5-10mm) transparent crystals in the bottle. I tried to mix rodinal many times, but I always had only very small crystals (less than 0,5mm).... And one more thing I can't understand - if I add more NaOH, crystals will dissolve, yes, pH will reach 14, but where are the crystals, which are in Agfa's developer?
The crystals dissolve when more alkali is added. The pAP is a weak acid and needs a large amount of "excess" hydroxide to force the salt to dissolve by forming the Phenolate.