Burning odor from sod. metabisulfite

[jim appleyard]

I was mixing a new batch of Pyrocat HD and when I added the Sod. Metabisulfite to 100F distilled water, my nose and throat began to burn. I re-capped the jar and went outside for fresh air. I finsished mixing the formula some time later. Why would this happen? I've mixed several batches from this same jar before and had no issues. Does Sod. Metabisulfite break down into something else over time?

I'll mix from the start outside next time, just to make sure.

 

[Prof_Pixel]

Sodium metabisulfite releases sulfur dioxide in contact with strong acids:
Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2

On heating to high temperature, it releases sulfur dioxide, leaving sodium sulfite behind:
Na2S2O5 → Na2SO3 + SO2

Either way you get SO2 which is very unpleasant to breath!

 

[Athiril]

Sulphur Dioxide. It builds up inside a large jar of the stuff heating or no heating so don't open it under your face.

 

[Jim Noel]

The chemical needs to be kept in cooler conditions, and a respirator worn while mixing.

 

[Gerald C Koch]

Sodium or potassium metabisulfite can be considered as a solid container for sulfur dioxide gas. Sulfur dioxide can cause a serious asthmatic attack in sensitive individuals. Use a respirator or work outdoors. There should be no need to heat the water for solution A as all the chemicals are readily soluble in water.

 

[jochen]

Hello,
if your sodium or potassium metabisulfite does not have this odour any longer, it has decomposed and does not work. A further rectuion is the oxidation of the disulfite or the sulfite to sulfate by the oxygen of the air. This occurs also with sodium sulfite which is stored open or in containers that leave oxygen in like PE-bags.

 

[Ian Grant]

Jochen's point about the lack of the smell is important. Pyrocat HD (part A) made up in water with fresh Metabisulphite will last up to 30 months in a good unopened bottle, the bottle must be glass or high density plastic. With old Metabisulpite with little smell and a poor quality plastic bottle shelf life is a few weeks.

It's worth noting that Sodium Bisulphite doesn't give off as much SO2 as the Metabisulphite and has slightly different industrial uses because of this, they aren't the same JT Baker sell both, Sodium Metabisulpite is 100% Metabisulpite < 0.001% Bisulpite.

While you can buy analytical grade Bisulphie wch is pure it's also unstable, the commercial/bisulphite is a mixture of Bisulphite and Metabisulphe withe the balance being beteen 40-90% Metabisulphite.

Where the Metabisulpite is being used as an anti oxidant you need the freshest/pirest you can get.

Ian

 

[jim appleyard]

Thanks all, interesting stuff! My chems are stored in a cool place, but I will surely mix this one outside next time.

Would the substitution of Potassuim Metabisulfite be acceptabel in this dev? I know that used in rodinal, but not much else. Haven't seen Sandy King on this forum in quite awhile. He might know or have input, after all, it's his dev.

 

[john_s]

A thought process going on with me here: I was writing this when I had second thoughts: "I have read that you don't want much potassium getting carried over into your fixer, as it reduces fixing efficiency, but I use potassium carbonate in my print developer because of its higher solubility (i make up a concentrate) and I don't have any problems." BUT I did have problems similar to those of the OP (see my post above) which went away when I stopped using a water rinse between dev and fix and started using an acid stop (sodium metabusulphite in my case). Maybe my problems were caused (or at least slightly aggravated) by some residual potassium in my FB paper which reduced fixing efficiency, and which was better washed out by acid stop.

Just conjecture, but what I'm doing now works.

So to have a stab at answering Jim's question about potassium metabisulphite, maybe not advisable. I get my sodium metabisulphite at a home beer brewing supplier and it's quite cheap.

 

[Ian Grant]

The amount of Potassium carry over isn't going to affect the fixer, almost all commercial liquid paper developers use Potassium salts because of their solubility. Also Potassium salts are used in some commercial fixers with no ill effects.

You'rev problems were caused by alkali developer carry over when you didn't use a stop bath that will happen with Sodium or Potassium salts.

Ian

 

[Ian Grant]

Thanks all, interesting stuff! My chems are stored in a cool place, but I will surely mix this one outside next time.

Would the substitution of Potassuim Metabisulfite be acceptabel in this dev? I know that used in rodinal, but not much else. Haven't seen Sandy King on this forum in quite awhile. He might know or have input, after all, it's his dev.

Yes you can use Potassium Metabisulphite instead. Just adjust for the difference in MW multiply the sodium Metabisulphiteb amount by 1.17.

Ian

 

[jim appleyard]

Thanks all!