The Sulfite family: comparisons

Hi all:

Mixing formulas from scratch for years, I'm very familiar with sodium sulfite, but I realized that I now need to know about its other relatives. Could someone comment about these similar compounds, what they do, how they are similar/different from Sodium Sulfite, if they are also solvent, why you'd use them, etc:

sodium sulfate
sodium bisulfite
sodium metabisulfite

Thanks!

-Jarin

Sodium sulfite - primary preservative agent in the developer, after solution in water it creates slightly alkaline environment, so it can be used as the only alkaline agent required to start developing process. The preserving properties of sulfite are explaining it's oxidizing instead of developing agent to sodium sulfate;
Potassium sulfite - used as Sodium, but it is more soluble, so it's used in concentrates instead of sodium sulfite;
Sodium metabisulfite in water hydrolises to sodium bisulfite, so in photograpic solitions you can consider them as equivalent. But there are a lot of mess between these compounds in chemical dealers and the only way to find out what exactly you had buy is NMR analysis;
Sodium bisulfite - similar to sulfite, but it is an acid salt, so obviously it cannot be used as alkaline agent, it is usually used to get slightly acid environment in solutions;
Sodium sulfate - used in tropical developers, when it required to get temperature above normal. Do not have preservative properties, cause it it final oxidized form of sulfite. Not very usefull in photography.

Hm. Do sodium bisulfite and metabisulfite reduce stain in staining developers and give solvency effects like sodium sulfite? To they preserve developers by any means other than acidification (like sodium sulfite)?

J

Jarin Blaschke said:

Hm. Do sodium bisulfite and metabisulfite reduce stain in staining developers and give solvency effects like sodium sulfite? To they preserve developers by any means other than acidification (like sodium sulfite)?

Click to expand...

If you dissolve Sodium Sulfite or Metabisulfite in water, you get a mix of ions in solutions: Na+, HSO3-, SO3-- and, depending on solution pH, some free SO2. Obviously with Sodium Metabisulfite you get less Na+ and lower pH, but the general nature of dissolved ions is the same. Except for the effect of lower pH you should expect same behavior of Sodium Sulfite and Sodium Metabisulfite.

Sodium Sulfate is an entirely different animal, since it does not have the reducing power of Sulfite: it will not scavenge Oxygen, it will not protect developing agents, and it will not scavenge oxidized Metol or Hydroquinone. It does harden gelatin a bit, that's why it's used in tropical developers.

Bisulfite is an older term. The modern term being hydrogen sulfite which indicates that such sallts are sources of hydrogen ions. So sodium bisulfite is not interchangeable with sodium sulfite. You would have to neutralize the hygrogen ions first..

michael_r said:

A simplified way of thinking about this - whether you initially added sulfite or bisulfite/metabisulfite, in the working solution you basically end up with sulfite.

Click to expand...

It would be good to state that this simplification should be limited to developers, which are (almost) always alkaline (meaning a pH value higher than 7).

If the pH is lower, as is common in fixers, then substantial bisulfite ion can exist in solution along with the sulfite ion. It used to be a common industry practice when "regenerating" (desilvered) fixer or bleach-fix to correct "sulfite" levels by using a combination of both "bisulfite" and "sulfite" in order to get closer to the final aim pH. This minimizes the final additions of either acid or alkali needed to correct the pH.

One other comment on "sulfate" (not sulfite): this is also a result of oxidizing sulfite. So if you started out with a lot of sodium sulfite, then the solution was significantly oxidized, you will end up with a significant amount of sodium sulfate, along with the remaining sodium sulfite. Normally, though, you are more concerned with the loss of sulfite ion than with the sulfate increase. Actually, to be blunt, few people on internet forums need to be much concerned about either one because volumes are too low to worry much about anything - if one has a chemical problem they can just throw it awake and start fresh.

https://archive.org/stream/cu31924031226065#page/n195/mode/2up
It has been known since at least 1902, the date of this book, that metabisulfite is a preservative of pyro and it is kept separate from carbonate to keep a high concentration of the hydrogen sulfite ion.
Offhand I cannot think of any developers based on hydroquinone that are two part.

Ok, I am adjusting pyrocat MC to try and exhibit more speed and a little less stain. So, I will be including 1g/L of sulfite (and more metol). I am not coming from concentrates and it will be mixed from scratch directly to working solution in large batches. Used this way, is there then any advantage to using bisulfite or metbisulfite rather than plain sodium sulfite? Or is the only real advantage to using bisulfite/metabisulfite in preserving a concentrate solution A of a developer?

michael_r said:

In the case of the pyrocat developer family, the only real real advantage to using bisulfite/metabisulfite is to lower the pH of "solution A" for storage. If you are mixing directly to working solution you can use sodium sulfite or sodium bisulfite/metabisulfite. In the end it will all be sulfite in the working solution which has a high pH (all pyrocat variants are loaded with carbonate).

Click to expand...

Alright, slowly I'm learning. So if I use bisulfite, that won't ultimately lower ph adversely in a working solution? Now, do you suspect I would have any adverse effects if I use sulfite and ascorbic acid (from both the M and MC versions)? I'm trying to see if I can make a staining developer work with replenishment in a motion picture machine.

I'm thinking:

Grams per liter of working solution:
.1 Metol
.5 Catechol
1.0 Sodium Sulfite
.05 Ascorbic acid
7.5 Potassium Carbonate

Any reactions as to what to expect?

J

Sandy King liked the Pyrocat series because they work well in the rotary Jobo machines.
Maybe you can consider if your motion picture processing device operates in a way giving agitation and aeration similar to a Jobo, in which case it may work.

Alan Johnson said:

Sandy King liked the Pyrocat series because they work well in the rotary Jobo machines.
Maybe you can consider if your motion picture processing device operates in a way giving agitation and aeration similar to a Jobo, in which case it may work.

Click to expand...

Agitation in a MP machine is much different - In the dark the 35mm film comes off of a 2000' roll (called a "flat"), and the long strand is pulled on rollers sequentially through all the solutions.

michael_r said:

Regarding replenishment, note that in most cases, you have to design a specific replenisher for a developer (assuming it can be replenished). It's not as simple as just adding more developer. So here again, we can only guess at what will happen as the developer is used, development by-products accumulate, oxidation takes place, and more fresh developer is added. You might also need an iron/copper sequestering agent to protect the ascorbate..

Click to expand...

Would EDTA do it? Or would I need Pentetic acid?
I'm very new to sequestering agents...

J

Yes, that thread - I started that one too!

The working solution needs to last 4 hours with replenishment. Presumably the motion picture lab uses filtered water. Still needed?

If so, where do I find Pentetic Acid and how much to use per liter of working solution?

J

Gerald C Koch said:

Bisulfite is an older term. The modern term being hydrogen sulfite which indicates that such sallts are sources of hydrogen ions. So sodium bisulfite is not interchangeable with sodium sulfite. You would have to neutralize the hygrogen ions first..

Click to expand...

Sodium Bisulphite is a less pureform of Sodium Metabisulphite and has some Sulphite present, JT Baker make and sell both, their MSDS sheets show their different intended uses.

Ian

Jarin Blaschke said:

I'm trying to see if I can make a staining developer work with replenishment in a motion picture machine.

I'm thinking:

Grams per liter of working solution:
.1 Metol
.5 Catechol
1.0 Sodium Sulfite
.05 Ascorbic acid
7.5 Potassium Carbonate

Any reactions as to what to expect?

Click to expand...

Hi, I don't know hardly anything about staining developers, but I CAN tell you that this "working tank" formula won't work in a replenished system. In a real system, the film will release byproducts which generally affect development. The most significant is probably bromide. So at a bare minimum your tank solution should start out with some amount of something like KBr. Then when you design the replenisher you use the incoming volume, the replenishment rate, to dilute the working tank enough to keep the bromide at a more or less constant concentration.

In order to test this in a real system you need to get at least a handful of tank turnovers to approach the final equilibrium. A tank turnover means that you add roughly one tank volume of replenisher. The general idea is that adding one tank's worth of replenisher actually flushes out only about half of the original solution. So one tank gets you about halfway to the final equilibrium, two tanks about three-quarters, etc. During this seasoning you will also need to be processing actual film with the same approximate exposure as your intended MP film.

You could rig up a small scale test system to mimic a cine processor but the rate of oxidation and evaporation would be higher; adjustments to the replenisher formula would likely be needed.

I'm just trying to point out the difficulties of something that looks fairly easy on the surface.

I think, during formula development, at the very least you would need: some sort of consistent method of exposing test strips (a sensitometer, for example), a way to measure the results (densitometer), and some chemical testing gear. I think, at minimum, perhaps a good pH meter and perhaps a hydrometer. It might be useful to have an analytic procedure for at least sulfite (the Kodak H-24 manual used to be online - it has a basic procedure, I think). The processing lab you use may already have these capabilities, and if so it's probably better to rely on their expertise than trying to learn it yourself.

Jarin Blaschke said:

The working solution needs to last 4 hours with replenishment. Presumably the motion picture lab uses filtered water. Still needed?

Click to expand...

That's all? Then maybe you could just flush through the same developer at a very high rate. No matter the rate, it's almost certainly cheaper than the cost of developing a proper replenisher. Your lab might have effluent issues to deal with, though; check with them.

How will you test preliminary film, though? A half day on a cine machine might be a couple miles of film; I hardly think you would be willing to shoot that and trust it to a process where you don't know what the final exposure requirement will be? If I were your lab, I'd be real hesitant about doing this.

I know these are not things you're asking about, but I think they should be real concerns to you. Fwiw my knowledge comes mostly out of experience, using manufacturer-supplied expertise, not internet research. But doing color neg studio photography, not b&w MP. But we did run miles of film every day on cine processors (and vastly larger amounts of print material). And a full time chemist.

michael_r said:

Maybe at 4 hrs you can get away without an iron/copper sequestering agent. Not sure if filtered water will help much. These impurities often come from the other chemicals (for example sodium sulfite).

Click to expand...

Photograde sulfite doesn't have much iron, at only 1 g/l (Jarin's spec) might be less than water, depending... Way back when C-41 was relatively new we had some activity problems which we traced back to a high iron content in municipal water. The water department told me, "Oh sure, we expect the iron to be high because of high water levels in the river." It turns out that a common treatment for "turbidity" is to use ferrous sulfate (or similar) as a floculant to help clear the water, and more is needed when high water flows faster. So if your developer is that finicky with iron, it's worth checking with the municipal water department. Having DI water hauled in is probably feasible for such a low usage.

Fwiw, the developer will have to be mixed for much longer than 4 hours; it may take that long just to mix and fill the processor, depending on how they're plumbed. And no one with any sense starts up a cine machine without first running some sort of test strips and a scratch test.

Jarin Blaschke said:

Yes, that thread - I started that one too!

The working solution needs to last 4 hours with replenishment. Presumably the motion picture lab uses filtered water. Still needed?

If so, where do I find Pentetic Acid and how much to use per liter of working solution?

J

Click to expand...

It looks like it depends on the rate of replenishment.
If this is high, there should be no need for special measures to preserve the ascorbate.
It depends on the concentration of iron and copper in your water supply, the temperature etc but in Jobos Pyrocat MC lasts long enough to process the film without replenishment.

Thanks for all this. Yes, at some point I let the experts take over, but I'm still in a proof of concept stage. The machine takes 700 liters and once developer is mixed, it takes 30-60 minutes to run, check density on the test strips and adjust. With D-96 running speed, 90 feet of film pass a given point per minute. I imagine a daily batch of footage to be a maximum of 12,000 feet. So let's say 140 minutes to process all the film, another 60 minutes for the test strips and let's say another 40 for mixing and a cushion: 240 minutes or 4 hours.

J

Jarin Blaschke said:

Thanks for all this. Yes, at some point I let the experts take over, but I'm still in a proof of concept stage.

Click to expand...

You should really stop in and chat with your lab before you get too far along. Let em know what you have in mind. They can work out the details with you.

Once you realize how many monkeys are on your back, and who's going to be paying for them, you may want to change plans.

I personally think that you're in this over your head, but don't realize how deep it is.

If I were them, I'd have about 50 things to go over with you, a lot of them on the order of "If such and such a thing goes sour, who's problem is it?" The rest mostly along the lines of, "What are the specs and tolerances for such and such, how will we evaluate, and what do you want us to do if the process runs out of spec?"

The reason you don't normally get these questions is that everything is already established for the mainstream processes. The machines and the chemicals are designed to be compatible; chemical specs and troubleshooting procedures are already established, and the lab techs already know how to deal with things.

You might find that your lab is much more casual than I am, and willing to wing it the whole way; I dunno. I spent years as the QC manager in a large studio chain lab, running thousands of gallons of replenishers every day (albeit the vast majority from the print side); we didn't take chances with our studio film.

In theory slow down the film feed rate in proportion to the times taken to develop in D96 (which is known?) and in the pyrocat developer.
Calculate the output rate of developed silver grams per minute, and from this the minimum rate of replenishment of pyrocat developer required..
Use more than the minimum rate as this is an inexpensive variable.