Use of inert gases

[nmp]

- CO2 has some solubility in water, so the solution will absorb it to form carbonic acid reducing the pH.

- different gases have different densities, but it does not mean they separate as they are miscible in each other.

- If N2 is used, simply force it into the bottle at higher pressure which will displace the air, put the cap on and as long as it is airtight it will keep.


Instead, why not use something like this:


https://www.amazon.com/Kaiser-204198.../dp/B000L9MWDS

[Ulophot]

Many years ago, I read that holding one's breath for a good forty seconds or so decreased the ratio of oxygen in the lungs, so that exhaling into the developer container would help preserve the chemical. I have used this free source, having once used nitrogen sold for preserving wine, which simply cost too much at the time. I just looked up this phenomenon, after read this thread, since I couldn;t recall whether it was carbon dioxide or nitrogen which increased significantly in proportion. A long explanation written by a specialist contains a graph showing nitrogen plummeting as breath is held, so it must be the carbon dioxide that increases.

[Gary Beasley]

If you have the room and a tank and regulator nitrogen is pretty cheap at the airgas stores where you get welding gases. I paid $18 for a refill last time. Not sure what the argon would be but it shouldnt be outrageous.

[EdSawyer]

Argon is more than Nitrogen. I still have some stuff Beseler used to sell in an aerosol can, probably outlawed now, but it works well.

[Jim Noel]

Hi all, does anyone know how carbon dioxide reacts, if at all, when used to displace oxygen from B&w chemistry in storage bottles? I used to use nitrogen years ago for colour chemistry but was wondering about co2 as I think it’s cheaper. Or does anyone recommend some other inert gas for this use? Thanks

CO2 is NOT an inert gas.

[Drew Wiley]

Argon is commonly used. But that ordinary comes in big pressurized cylinders from welding suppliers. Wine-making supply shops sell smaller volumes, as well as some woodworking stores and on-line sources to keep varnishes fresh by displacing air. A totally different kind of trick involves ceramic micro-beads which float atop solutions to slow down oxidation; they're available from laboratory supply houses. My own answer is simply not to keep developers long enough for oxidation to have
an effect; and I never, ever re-use or replenish them.

[Joe O'Hara]

I would not use butane for this purpose. Actually I would not use it for any purpose indoors,
except under a fume hood, if I had one. It is crazy flammable.

CO2 will react with water to form some amount of carbonic acid. This is the acid in "acid rain" and
what eats the ancient marble statues standing outside. The sulfite or carbonate in developers will
scrub that but it's not helping the situation.

Argon or nitrogen are better choices. Or, you could just mix smaller quantities of developer or store it
in smaller bottles. Or, "canned air", usually some kind of flourocarbon mixture, but they usually (in the US
at least) contain "bittering agents" to discourage inhalation abuse, and who knows what they are.

I just mix enough to use it up in a month or so and don't lose any sleep over it.

[Joe O'Hara]

Clarification: Carbonic acid is not the only acid in "acid rain". Sulfuric acid (mostly from burning
coal, but also from volcanoes) is a bigger issue, but carbonic acid was dissolving marble and
other exposed rocks for quite a while before coal was mined.

[Eric Woodbury]

It's the CO2 in the atmosphere that is increasing the oceans acidity and dissolving the reefs.

I used N2 for many years with PMK in a drum (not the method in the book). I had a short tank in the darkroom. Works fine and is inert at normal temps. No reason to bother with Argon.

[Drew Wiley]

Accordion bottles were mentioned. These were once routinely available at camera stores. But they're still so poorly made with permeable thin plastic that I doubt that they were ever a serious answer. I prefer to decanter or split up developer volume into multiple small amber glass bottles, filled to the top. As for rotary processing, there are pyro tweaks much more resistant to aerial oxidation than PMK. But a related problem is how certain rotary drives (esp Jobo) run at unrealistically high RPM's, even at the lowest setting. I'd rather just roll the drum gently back and forth along the bed of the darkroom sink if I still did PMK rotary. I also have big custom drum machines with far more cooperative RPM's for color processing, which would be suitable for pyro.