Carbon Dioxide's effect on film developer

[BetterSense]

Just in my junk bins, I have everything I need to make a Nitrogen Burst tank agitator...except the Nitrogen tank, which I don't have the space or money for. But, I do have tons of paintball tanks and regulators, so I could use compressed air or CO2. CO2 doesn't have oxygen in it, but it is an acid, so does anyone care to guess how much of an effect CO2 would have on film developer in terms of dropping the pH?

 

[Vlad Soare]

CO2 doesn't have oxygen in it

Oh yes, it does. About 72.7%.

 

[Photo Engineer]

The Oxygen in CO2 has no effect on developer.

The CO2 itself dissolves in water to form Carbonic Acid which will drop the pH by a considerable amount. It should not be used.

PE

 

[Vlad Soare]

Carbonic acid is weak and very unstable at low pressures. The tendency of carbon dioxide to combine with water to form carbonic acid is very weak. It doesn't readily dissolve in water at normal atmospheric pressure. On the contrary, carbonic acid is very eager to decompose into carbon dioxide and water.
I have no carbon dioxide at hand to test this, but I somehow doubt that blowing it into a solution at normal pressure will cause a significant drop in pH.

 

[BetterSense]

I suppose I could monitor the pH of the developer with pH strips. How sensitive is developers' activity to pH? Is it something that could be monitored by pH strips (which only have a resolution of +- .5)?

 

[Gerald C Koch]

Forget using either air or carbon dioxide. Each will have a deleterious effect on the developer. Air will cause the developer to oxidize and lose strength and CO2 will change the pH. You have to use an essentially inert gas like nitrogen. Why do you think the method is called nitrogen burst.

 

[Worker 11811]

What about helium? You can buy that in just about any store that sells party supplies and the tanks aren't that big?

If you went to a welder's supply shop you could buy helium in one of those torpedo shaped gas cylinders. You just pay a deposit on the tank and return it when you're done or you exchange it for a new one.

You could chain one of those gas cylinders up in the corner of the room and run a hose where it needs to go. It wouldn't take much space at all.

 

[Bob-D659]

What little CO2 that dissolves will react with the alkali in the developer, so over time the ph will drop a lot. Yes helium will work, so will argon, N2 is used because it is the lowest price of the compressed gasses if you are buying in decent volumes, and a K cylinder once a year is not a decent volume, even one a day is pretty low volume in the compressed gas business.

If you had the funds, rent a large N2 cylinder and buy a fill adapter for your paint ball tanks.

 

[Photo Engineer]

The last I checked:

4 ft Tank ~$250 (to own - you can rent them more cheaply but costs mount over the years)
Refill ~$ 30 (lasts years even with constant use)
Pressure reducing valve ~$150 (I had 2 and gave one away - too bad!)

You can get lab tanks of N2 that are about 1 ft long and about 4" in diameter. These used to cost about $10 with everything you need to get to work.

I own my own tank and valve. The last refill was about 10 years ago. The pressure is still up near the top. I use it to top off all tanks.

Now as for CO2 damage. An open tray of Dektol will drop by about 1 - 2 pH units in a day. A closed plastic tank of Dektol will begin to collapse if stored with just air. CO2 dissolves rapidly in Alkali and tries to bring the pH down to the value of pure Carbonic Acid, by neutralizing all of the alklai. THis will happen given time but usually takes a while with just air. BUT, over the life of one tank of developer topped with CO2 (remember the OP wants to use pure CO2 - not air), you can look at the pH moving from 9 or 10 down to about 7 within a few days, if not hours. The plastic container will buckle inwards perhaps crackiing and you will lose your developer no matter what.

PE

 

[BetterSense]

I currently use one-shot developer. So the question isn't what will happen over a period of days, but rather what will happen over maybe 3 batches of sheet film, developed within a few hours of each other, with nitrogen/CO2 burst agitation when actually developing.

 

[Photo Engineer]

The pH will drop with CO2 agitation and the contrast and density will go down!

In addition, the developer will be sucked into the sparger due to the dissolution of CO2 into the developer and the sparger can become plugged with Carbonate salts. If you move the sparger with the processed film, you risk cross contamination.

I'm sorry I misquoted from the OP. You did indeed want to use CO2 agitation and not storage, but the final result is pretty much the same.

PE