Awful smell from hypo

[ColinRH]

I have been making salt prints for the past 10 years and only occasionally use 35mm camera.
I decided to take the OM out and first thought to test some film.
I used Delta 400 to dev in my usual pyrocat-HD.
I made the solution up as usual, dev'd the film, gave a simple citric acid stop and poured in my usual hypo. It was absolutely fresh but after some 30 seconds the most awful bad eggs smell rose from the Paterson tank.
When I poured it out it had turned completely milky and failed to clear the film.

There would appear to be some cross contamination but I'm unable to think of anything. Citric acid and hypo???
Any suggestion might help.

 

[Ian Grant]

You need to clarify "usual hypo". are yo using a commercial fixer or sodium thiosulphate ? Whichever the thiosulpate is breaking down to form sulpurncompounds.

Ian

 

[koraks]

What's the concentration of your stop bath and how old was the bottle of fix (in addition to the questions above)?

 

[ColinRH]

Ian: I use Sod. Thiosulphate at the rate 125gm to 500ml. As the hypo I’ve got is pentahydrate I made the assumption that is should be multiplied by 1.7 so added 212gm. To 500ml water.





Koraks : Stop bath was 5gm to 500ml water and was mixed about 6 minutes before it was used.

I mixed the hypo yesterday evening and today’s film was the first (and last!) to go into it.



The transformation in the tank took only just a few seconds!

 

[pentaxuser]

So the sodium thiosulphate was freshly mixed and then used say 12-15 hours later. The citric acid was also completely fresh. The tank was drained of developer and then drained of stop then hypo added. Within 30 secs the sulphurous smell arose and the hypo was milky when poured out after the normal fixing time.

On the surface I cannot see how this is possible based on what I think you have said based on my summary. When you say failed to clear the film it might help if you say what the film looked like and whether the film was fixed enough to verify that the developer had worked. I say might help but this is me clutching at straws really

At the risk of appearing to insult your intelligence I am tempted to say that either something else was involved but I know not what, since if everything was exactly as you think it was in your description then isn't what happened impossible? It sounds on the surface that the ingredients for the hypo have somehow "gone off"

pentaxuser.

 

[Ian Grant]

The problem is that during fixing there are many different silver thiosulphate intermediary complexes formed, these a series of equilibrium products. In some biological processes the presence of Citrate helps liberate Hydrogen Sulphide as Thiosulphate decomposes. You've had something like that happen.

Plain Hypo fixer isn't that stable adding salts like Sulphite or Metabisulphite help tip the equilibrium balance in the direction and also help issues issues like yours. Somewhere I have a page I drew up over 40 years ago of the intermediary complexes formed during fixing.

Ian

 

[nmp]

The rotten egg smell and the milky solution are the signs of hypo reacting with an acid. The former is the SO2 and latter elemental sulfur which precipitates. (see my correction below) So how did this happen. I would try and repeat the same sequence without the film just to make sure it has nothing to do with the film itself. Also, why not introduce a plain water rinse before fixer. For salt prints, I use sodium carbonate (2%) which is supposed to deter this reaction from taking place if there is an acid carry-over from an earlier step. Or sodium sulfite should work as a deterrent to acidification (and stability in storage) too. I think Ilford spec for the film recommends the rapid fixer that includes sodium sulfite, if I am not mistaken.

Edit/Correction: I mixed up the egg smelling H2S with a more noxious SO2. Thanks for railwayman3 for pointing it out. So while whiteness could be precipitated sulfur, the egg smell could be something else. Egg on the face....

 

[railwayman3]

The rotten egg smell and the milky solution are the tell-tale signs of hypo reacting with an acid. The former is the SO2 and latter elemental sulfur which precipitates. So how did this happen. I would try and repeat the same sequence without the film just to make sure it has nothing to do with the film itself. Also, why not introduce a plain water rinse before fixer. For salt prints, I use sodium carbonate (2%) which is supposed to deter this reaction from taking place if there is an acid carry-over from an earlier step. Or sodium sulfite should work as a deterrent to acidification (and oxidation in storage) too. I think Ilford spec for the film recommends the rapid fixer that includes sodium sulfite, if I am not mistaken.

If I remember my school chemistry (and school "stink bombs" ) correctly, the bad egg smell is hydrogen sulphide, (Sulphur dioxide has a rather nasty strong smell, with burning sensation in the nose.) But Wiki says that hydrogen sulphide can be smelt at 0.00047 parts per million, so it would probably take very little citric acid carry-over to cause a distinct smell.

 

[nmp]

If I remember my school chemistry (and school "stink bombs" ) correctly, the bad egg smell is hydrogen sulphide, (Sulphur dioxide has a rather nasty strong smell, with burning sensation in the nose.) But Wiki says that hydrogen sulphide can be smelt at 0.00047 parts per million, so it would probably take very little citric acid carry-over to cause a distinct smell.

You are right of course...I mixed up SO2 and H2S.

 

[ColinRH]

Thanks for all your input, it is an odd problem but perhaps it is beginning to unravel - and, pentaxuser, if you are insulting my intelligence don’t worry. These days the old brain is not as agile as it used to be and the following may just illustrate that.

My workspace calls for a bit of creative juggling; pouring out one chemical into a reserve container until it is required again etc. Last week I tray dev’d 2 sheets of 5x4 Wephoto FO5 Lith film in Multigrade developer. I’ve not used the film before and as a quick trial used the MG dev which was out of date - not miles out but still ood.

I do now remember that there was an odd smell when I put the fix in and it became a very dark brown colour. The required fix seemed to do its job so I thought nothing more of it and poured the fix back into my fix concertina bottle to be used for the second sheet of film. I dev’d the second and the smell became stronger when the fix went back in. It seemed to fix so I then disposed of the fix.

So...I wonder whether what happened with the fix and the lith film last week may have left some in the container which I used for the fresh fix last night.



To me that doesn’t give an explanation of today’s issue but to you chemistry buffs it may.

If it was caused by last week’s smelly fix what caused that? Old MG dev, or some chemical used for the wephoto lith film?

 

[Ian Grant]

The rotten egg smell and the milky solution are the tell-tale signs of hypo reacting with an acid. The former is the SO2 and latter elemental sulfur which precipitates. So how did this happen. I would try and repeat the same sequence without the film just to make sure it has nothing to do with the film itself. Also, why not introduce a plain water rinse before fixer. For salt prints, I use sodium carbonate (2%) which is supposed to deter this reaction from taking place if there is an acid carry-over from an earlier step. Or sodium sulfite should work as a deterrent to acidification (and stability in storage) too. I think Ilford spec for the film recommends the rapid fixer that includes sodium sulfite, if I am not mistaken.

Edit: I mixed up the egg smelling H2S with a more noxious SO2. Thanks for railwayman3 for pointing it out. So while whiteness could be precipitated sulfur, the egg smell could be something else. Egg on the face....

Fixers acidified using Acetic Acid don't give of Hydrogen Sulphide, so it's not so simple.

Ian

 

[KN4SMF]

Sodium thiosulfate is the fixing chemical, but when mixing up the fixer, sodium sulfite is a vital addition to the formula. It's what keeps acidsfrom breaking apart the sodium sulfite into the constituent elements, sulfur being one of them. Hence the smell.

 

[nmp]

Fixers acidified using Acetic Acid don't give of Hydrogen Sulphide, so it's not so simple.

Ian

Yes....Ian. I edited my original post to reflect my confusion. H2S requires some bacterial activity as you pointed out earlier.