If a solution of p-aminophenol in alkali is neutralized with acid, a precipitate ,almost certainly the free base, is formed.
I have done this.
Metol in alkali is like p-aminophenol with an extra CH2 group,it probably has similar chemistry.
It may be that metol will dissolve eventually but not a myth that sulfite greatly slows the process down,and that this is due to the formation of metol base.It would be easy enough to test the rates of solution with and without sulfite.
Sodium sulfite is sufficiently alkaline to release the Metol free base. Remember that D-23 works as a developer because the solution is still alkaline even after 7.5 g of metol have been added.
My objection was in the blanket claim that Metol will not dissolve in sulfite solutions. It WILL dissolve but at a slower rate. If it didn't then such developers as D-23 or D-76 could never be mixed no matter in what order the chemicals were dissolved for as soon as the sulfite was added the Metol base would precipitate out.
Last edited by Gerald C Koch; 02-01-2013 at 10:15 AM. Click to view previous post history.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.
The problem with Metol and Sulfite (or probably any alkali) is not that the latter causes the former to precipitate out. It doesn't and there are plenty of working developer formulas loaded with Metol and operating at high pH. The issue seems to be that Metol crystals are slow to dissolve when the solution is already alkaline.
And I really don't think Kodak's solution is as simple as writing in the manual to use hot water to mix D-76. Note Kodak holds patents for encapsulating compounds to make them go into solution later than they would do normally, and this gives them the option to dissolve different compounds in one powder in a preset sequence.
Trying to be the best of whatever I am, even if what I am is no good.
The "encapsulating" compounds are what I expected were involved in Kodak's single packaging. I assumed something like this kept the sulfite from dissolving before the Metol. It was just a guess though as I don't have anywhere near the chemistry knowledge required to make that claim with any kind of certainty.
Also interesting is the wording used by Haist when he talks about mixing practices and why Metol must be dissolved before sulfite. He says the Metol must be dissolved first because it precipitates in a sulfite solution. This seems an odd choice of words since in my mind "precipitation" is when a substance already dissolved comes out of solution. If Metol actually precipitated in sulfite solutions than as Gerald says, it wouldn't matter if the Metol went in before or after the sulfite. Again though, I'm in over my head as far as the chemistry goes so what I'm saying might be nonsense.
Last edited by Michael R 1974; 02-01-2013 at 10:43 AM. Click to view previous post history.
I always figured the pinch of sulfite was to neutralize the dissolved oxygen in the water. But since testing water for dissolved oxygen at work, I've learned that at 20C oxygen saturates in water at about 8 mg/L. That's not a lot of oxygen so it's really not that big of deal.