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# Thread: My chemicals ate air!

1. I do not believe that 21% of oxygen manages to get into the chemicals. That's just improbable. Barometric pressure changes is much more likely.

2. make sure your bottles have tight caps!
i had a bottle and the cap wasn't tight
and i had a heck of a time pulling my
sink out of it. the time before i used a cork
in an amber glass bottle ( yeah i know cork isn't
a good thing to use ) and the next time i went into
the sacred space, my enlarger was sticking out of the bottle.
now .. i use a screw-top bottle ( still amber glass )
and my chemistry goes into a safe ...

3. Then think about how many grams of "air" there is in a bottle. One mole of a gas will expand to 22.4 liters at room temp. If there is 1 liter of air in the gallon bottle, then there is 1/22.4 mole of "air" in there, and air being mostly nitrogen and 21% oxygen, we can say there is about 1 gram of air there, so about 1/5th of that is oxygen. So about 0.2 gram of oxygen. It doesn't seem like much of a stretch to me to have the developer react with 0.2 gram of oxygen. THat would be all 21% of the oxygen in the bottle. Not so much when you think of how many grams there are.

4. John, I hope that is an air-tight safe!

5. Kirk,

but the story goes on: with the next opening, to take some minor volume off, the gaseous volume will, in the worst case, be substituted by new air. So there will be 0.2 gram again.

6. Originally Posted by Kirk Keyes
John, I hope that is an air-tight safe!
i keep it outside, just in case!

7. Originally Posted by ic-racer
In a closed container, there is an equilibrium between the pressure of the gas in the bottle and the vapor pressure of the liquid. The vapor pressure of the liquid can change considerably with changes in ambient temp. Thus causing the plastic bottle to 'cave in' when it is cold and 'bulge' when it is hot.
I think this is the most likely answer. If you, like I, mix your chemicals at the maximum recommended temperature, say 80F, and then seal the bottle and let it cool, it will contract.
Next time, let the solution cool with the cap loose and then tighten it, and I'll bet it won't happen.

8. Originally Posted by Akki14
I do not believe that 21% of oxygen manages to get into the chemicals. That's just improbable. Barometric pressure changes is much more likely.
Heather, I do believe that developer "consumes" oxygen, let me explain. I keep my print chemical solutions in plastic fizzy drink bottles. At the end of the printing session, everything gets back to the bottle. Everything is stored at the same place, resulting in same pressure(s). One day later, the developer bottle has shrunk, not the other two. IIRC, stop bath doesn't oxidise, it's acetic acid with a tiny amount of indicator. Fixer has ingredients that can oxidise (sodium sulfite does), but it's bottle volume remains the same. It seems it's the developing agents that have the tendency to react more rapidly with oxygen.

FWIW, using lighter gas (propane - butane mix) seems to prevent this. Of course, initially the lighter mix has low temperature, so pressure inside will increase significantly. I tried loosening the cap, thus equalising the pressure inside and outside the bottle (you can hear the gas escape). If I let it for a day or two (or more) the bottle's volume doesn't change.

9. Originally Posted by Kirk Keyes
Although Dancqu loves single shot fixers,
I prefer using two-bath fixing.
I'll expand on that:
"... fresh each session, very dilute, single shot fixers,
using minimal solution volumes, ..."

Such fixers can have good chemical milage and 'archival'
levels of dissolved silver from one fix, with no testing
needed. A space saver. Integrates nicely with single
tray processing. Films and papers wash fast with
less water.

If my volume of prints and films warrented AND
space were abundant I'd go two-bath. Dan

10. Sorry, Heather, but science is going against you with this one....and also against what I observe regularly (running a teaching darkroom, we have many bottles of developers, stop, fixers, etc.). This always happens to partially filled tightly sealed plastic bottles of developers -- and as anon notes -- never to bottles contain non-oxidizing chemicals. And if the bottle is glass, one hears the intake of air as it gets sucked into the bottle as one unscews the cap.

I do not believe that 21% of oxygen manages to get into the chemicals.
It is not 21% of the oxygen, but almost 100% of it -- which comprises of 21% of the normal air around us.

If a chemical reacts with oxygen, it will react with it until there is no more oxygen it can react to (or until the chemical is completely oxidized). This is the reason the shelf life of a developer in a half-filled bottle is only a third of that of a full bottle (both tightly sealed). And why a tray of Dektol, even if not used, will die within 24 hours...all that surface area and an unlimited amount of oxygen to react with.

The problem is made worse every time one opens up the bottle to use a little of the developer -- the partial vacuum created by the removal of the oxygen from the air above the liquid, sucks fresh air into the bottle, providing even more oxygen for the developer to react with and killing the developer faster and faster.

ic-racer. What you say is partly true. But there is not an equilibrium in a freshly sealed half-filled bottle of developer. Chemical reactions are taking place...oxygen gas is being "consumed" (changed from O2 to new chemicals with oxygen atoms freshly attached to them) by the chemicals of the developer. Once all the available oxygen gas is "consumed' and removed from the air space above the liquid, an sort of equilibrium is reached, if that would is the proper word for an unstable chemical (developer). From that point, changes in temperature will affect the vapor pressure inside the bottle -- but it is insignificant compared to the reduction of the pressure inside the bottle due to the removal of oxygen gas.

And there is some reduction in pressure inside of a sealed bottle of a hot liquid once it cools down -- enough to suck in the sides of a plastic bottle if there was some air space in the bottle. But that is not what is happening to a partially filled bottle of developer. Chances are that the liquid was room temp when the cap was put on, after all, it is partially empty because one has been using it over an amount of time...time enough to cool down.

I remember my 7th grade science teacher having a gallon gasoline can on a bunston burner on his desk -- after the little bit of water inside of it boiled, he took it off the flame and screwed on the cap, and went on with the class. As the can cooled, the sides started to cave in dramatically and with much noise. An impressive experiment -- got our attention!

Vaughn

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