Dilution problem of sodium sulphite in water

[Clement Apffel]

Hi everyone,
I have a very dumb question I think. I browsed the forums a bit for the answer but it seems nobody is as dumb as I am !

I've recently started to do pyro processing with Tanol with some success.
But I encounter a problem with the sodium sulfite solution.

I use anhydrous sodium sulfite and I dilute 10g in 1L water for that 1% solution at the end of the pyro process.
And I have big troubles actually diluting the sodium sulfite completely.
It seems to always have residues of undiluted crystals in the solution no matter what I tried :
Dilute in cold water, in hot water, dilute it in a small volume then add more water, dilute in the full volume from the start, trying to give it time, sometimes almost 48h with agitation every couple of hours, etc...

And it is pretty annoying because the crystals of course kinda stick on the film. So much that even after extensive washing, some residues will still be found on the surface of the film.

The very awkward solution I have adopted so far is to do a last wash under the sink as you would wash a plate, gently brushing both film surfaces with my hand, to remove the crystal residues.

I am obviously doing something wrong about that sodium sulfite solution and dilution, and I'd really like to read more experienced users about that !
It would help me a lot.

Last piece of information that might have some impact on dilution (I don't know), the water I have at disposal is rather hard, if not very hard. Would that be an obstacle to proper sodium sulfite dilution ?

Thank you in advance !

[Andrew Tymon]

I use distilled water for mixing up chemistry as my tap water varies, this way I'm assured consistancy.

[LabRat]

10gm/liter is a low dilution compared to other developers, and should dissolve well into solution, so I think there is an issue with the batch of SS you have, like it has too much moisture or something...

Try mixing with a magnetic mixer in hot water, and if still not mixing completely, it surely is a bad batch...

Steve K

[PRJ]

I've had issues with SS in the past when it ages. Can't remember specifically the chemistry of it, but it definitely changes and becomes hard to dissolve. Ruined a batch of Rodinal with some once. You'll have to replace it.

[Doremus Scudder]

Likely impurities in your sodium sulfite that are insoluble. 10g/liter go into solution quickly and easily at room temperature. I mix my own wash aid with sodium sulfite at 20g/l at processing temperature and never have a problem. The sulfite dissolves in a couple of minutes or less.

Maybe filtering your solution after mixing to remove the particulates will work for you, if you can filter fine enough so that you have no particles to adhere to the film. Good coffee filters or lab filter paper.

Best,

Doremus

[Drew Wiley]

How hot is your water? You need at least around 110F for consistency. Very small volumes might dilute lower, but I don't recommend it.

[Clement Apffel]

Thank you everyone for you advices and insights !

It made me feel less dumb haha.
I'll try to dilute my next batch in very hot water. I don't think I tried 45°C water yet.

But from what I read, my ss batch might have a problem indeed.

[Greg]

Years ago acquired dozens of white plastic 1 and 5 pound cans of Kodak Sodium Sulfite from our state's surplus store for pennies on the dollar. I'm guessing they were from circa the late 1980s. Bottles do not have (unopened) seals on them but just black screw on caps. One time I went to mix the powder from one of the bottles that I had started to use, also had some particulate grains that did not want to dissolve. At the time next to my office was a lab that did tox screenings. Asked one of the lab personnel and he told me to just throw that jar out since I did not know where the jars came from nor how they were stored. Since then when I start using a new jar I pay attention to how easyly the sodium sulfite dissolves. Sidebar: I also acquired a case of packets of Kodak XTOL again probably dating from the 1980s. Found that in maybe half of them the powder had caked up (I'm guessing from poor storage) and ended up throwing all of them away.

[tgtaylor]

I mix SS and ST (fix) in transparent 1L beakers stirring, while holding up to a window, with a paddle until every particle is completely dissolved and the solution is clear throughout. If you stop stirring and allow the solution to slow to a stop, you'll see the undissolved particles gather into a cloud. At that point I've found a more aggressive stirring accompanied with reversing the flow, will force many of the undissolved particles into solution. At that point continue "twirling" the paddle and stopping the flow to see the status. Stop when there are zero particles seen floating in the solution. When the cloud decreases in size, you can also let the solution sit for a few minutes and the particles will dissolve into solution without further agitation. However all check by stirring with the paddle up to the light that there are no particles floating around. The whole process doesn't take that long.

The process with XTOL is the same although I use a floating-lid tank that isn't transparent. Instead I have a large flashlight that uses 2 C cells batteries and shine the light through the mixture to observe the status of dissolution. XTOL has the tendency to cake-up on the bottom of the tank - especially if to pour it too fast while stirring - so you have to look out for that. But the process is the same as above only that there are 2 powders to dissolve. The whole process takes me 45 minutes to a hour to mix a 5L tank.

[Bernice Loui]

During the years when mixing B&W chemistry from powder, a good solution to this problem was to use a magnetic stirring plate with a magnetic stirring bar in a mixing beaker or Kodak glass graduate. Warm up the filtered water or distilled water to no less than 100 degrees F, not more than 150 degrees F (Kodak Graduated are made of thick glass that helps hold heat) put the glass container on top of the magnetic stirring plate with the magnetic stirring bar inside. Adjust the mixer speed to get a reasonable water tornado inside the glass container then gradually add the powdered chemistry. Run the magnetic stirring bar until all powdered chemistry is fully dissolved.

Works good with not a lot of work or fuss.


Bernice