Chemistry

[Ed Sukach]

I'd LOVE to use Argon. Try to find the stuff in containers small enough to be economically justifiable for a small, low volume lab.

I think I understand what you are saying about "bubbling" an inert gas through the solutions. Good idea, but the instructions included with the chemistry state an increased shelf life when the air in the unoccupied bottle space is displaced by "Protectan" spray ... which is a butane/ propane mix -- and is NOT available on this side of the ocean.
"Bubbling through" wold be nice, but I'll operate in a "better than nothing" mode for the time being.

BTW, Ole -- I am being careful with the liquified butane. At first, I thought I saw a difference in the level of liquid in the transparent reservoir, but a one- or two- second burst results in far less exhaustion of the supply than I first thought.

I was thinking of a way to measure the amount of butane actually dispensed ... I first thought of weighing, before and after ... but now ... I think I'll try using a toy balloon over the torch orifice, and try to guess what the volume of a short burst would be.

I have a LOT of respect for LPG. Many moons ago, I was a Lieutenant on the factory FIre Squad where I worked. We had many training sessions - lectures - and 'on hand" exercises on fire fighting.
One of the visiting instructors travelling to our company, in a rented car, attempted to light a cigarette with one of those disposable lighters. The thing went OFF!
He arrived minus eyebrows, what looked like fresh tan, and a partially fused polyester-blend suit - to a class in fire fighting!

 

[b.e.wilson]

In my experience bubbling an inert gas (I prefer argon but there are others) through the solution works very well and is cost-effective. The principal is simple: the inert gas displaces the dissolved oxygen. Additionally, argon is denser than ‘air’ so it also displaces the ‘air’ above the de-oxygenated solution and this prevents oxygen from reentering into the solution (providing that your seal is air tight) and negating all the effort you put into degassing it in the first place.

Two items of clarification, from a chemist's point of view:

the "simple principle" you mention above is called Henry's Law, which states that the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the solution. The oxygen leaves the solution because the oxygen containing solution is in contact only with oxygen-free inert gas, so it exchanges out of solution into the gas phase and is removed as more inert gas displaces it. The new gas then dissolves (its pressure over the solution having increased via bubbling). Strictly speaking one gas cannot displace another (as if only so many gas particles can dissolve at any one time), but sparging (the proper term for bubbling a gas through a solution) looks as if that is what's happening.

You cannot layer a dense gas under a less-dense gas for very long. The average absolute speed of a gas molecule is simple to calculate: average speed = SQRT(7,400,000/M.W.), where M.W. is the molecular weight of the molecule in grams per mole, and the speed is in meters/second (keep in mind that gas particles rebound as they travel, so one particle never moves in a straight line very long before bounding back the way it came, but the speed will tell you how quickly two gasses will mix together). For oxygen (32 g/mol) we get 480 m/s. For Argon (40 g/mol) we get 430 m/s. Not that big a difference. For butane (C4H10, 58 g/mol) we get 360 m/s, and difluoroethane (C2H4F2, 66 g/mol) we get 334 m/s. My point here is that layered gasses diffuse rapidly because the molecular speeds of all gasses at room temperature is very fast, much faster that any gravitational effect trying to keep them separate could withstand. Even layers made from two miscible liquids (water, d = 1 g/ml and ethanol, d = 0.82 g/ml) will be completely mixed in a week because of diffusion. I've never done it, but I'd guess two gasses, even if they could be initially layered (turbulence during the introduction of the second gas under pressure makes that unlikely), would last hours at most.

As has been mentioned, the only way to protect an oxidizable solution from oxygen is to sparge with an inert gas to remove the oxygen from the solution and the headspace, or store at reduced temperatures to lower the oxidation reaction rates. Or print enough so you don't need to store developers for more than a few days. I recommend the latter.[/quote]

 

[uma]

i have tried the last option,(printing enough) and it works just fine,

 

[sbaggett]

A lot of replies for a simple problem! Here's my 2-cents worth. I just displace the air in partially filled bottles in my kits (5-gal, 10L, etc). I use E6 and C41 1-shot and use nitrogen to make the chems in the partially filled bottles last longer. I went the nitrogen path and my friend went the propane path. He buys propane bottles from the hardware store (for small propane torches) and sprays some in his bottles in the same manner I do with the nitrogen. I bought the first 80-cu-ft tank and regulator for $175 US, total. Thereafter, I pay $11-$15 US for the next tank (industrial grade). Each tank lasts 3-6 months. I also flush the top of my Jobo bottles containing RA-4 if I don't use it up in a printing session. I can state that an E6 kit will last at least 6 months and a C41 kit will last at least 3 months just by nitrogen-flushing most of the air out of the kit bottles after mixing one shot amounts. I've never kept either kit longer than this before using it up, but I'll bet they will last something near the unopened shelf life.

 

[Boris]

There is such a thing called Private Preserve to preserve wine. They have a website privatepreserve.com. What they have is a combination of N2, Co2, and Ar. One can cost about $8.00. This should work for the photo chemicals.

 

[Jim Chinn]

Ed, you might want to try a scientific supplier for schools or colleges. You can buy smaller bottles for gases, about the size of a small home fire extinguisher. There is a term for the size but I don't remember it right now. You can take them to any welding supplier and have them refilled.

 

[b.e.wilson]

There is such a thing called Private Preserve to preserve wine. They have a website privatepreserve.com. What they have is a combination of N2, Co2, and Ar. One can cost about $8.00. This should work for the photo chemicals.

Carbon dioxide will react with a basic solution (which most developers are) very quicky to neutralize it. Avoid CO2 at all costs. It will react and leave a negative pressure in the bottle, which will suck air in.

Might be OK for ascorbic acid developers, though.

 

[uma]

hi
but i think CO2 will be dissloved with tank solution and increase it 's pH by oxidation.
uma

 

[Ed Sukach]

Update on the Butane Application for Preservation...

Yesterday I developed six (6) rolls of AgfaColor Optima 400, using Tetenal CN2 chemicals previously opened and partially used on 18 December 2003. Butane from the BernzOMatic torch* was applied over the chemical surface, the bottles re-capped, and stored at ambient darkroom temperature (~ 21 C). Just used this "set" for yesterday's development, and everything is *fine*.
Test strips analyzed with the ColorStar show less than 3cc color variation in any direction - on a par with *usual* processing.

I've "re-butaned" this set. I'll try it again in a couple of months.

Looks good - I think I've found a viable substitute for "Protectan".

* No! No! The torch wasn't lit!!!

 

[Jan Brittenson]

hi
but i think CO2 will be dissloved with tank solution and increase it 's pH by oxidation.

How would I go about to empirically test this hypothesis?

I could take two jars and put a few fl oz of the same batch of TF-3 fixer in both. One gets a protective gas, the other just the air in the jar. After a couple of weeks I compare the clearing times to see if there's a difference. The idea is that the jar that's full of air will provide an accelerated oxidation. Would this be a suitable test? I'd get a baseline clearing time at the start of the two weeks, to compare any protective benefit against.

 

[b.e.wilson]

Don't bother. Umas hypothesis is wrong. CO2 does not, and cannot increase the pH of any solution into which it is dissolved; it can only decrease the pH of a solution if it is greater than 5.6 (carbonic acid is formed when carbon dioxide dissolves in water).

I don't know what is meant by oxidation: is CO2 supposed to oxidize something, or is it oxidized? I'm certain CO2 is already as oxidized as it can be, but have no idea what might be in a developer/fix that would be oxidized by an oxidant as weak as CO2.

As for the test, if your fix has a pH less than 5.6, then CO2 should work nicely as a protectant. For most developers it will lower the pH and render them unusable.

 

[Flotsam]

What Luck!
I just ran across a mini bonanza of 4 long forgotten cans of Beseler XDL. I must have bought them long ago when it was becoming hard to find. I've been happily using Butane since reading the discussion here.

 

[Shmoo]

At one point in time, I posed the question of using "Private Preserve" on photo chemicals to the company. The response from Scott Farmer at PP was as follows:

"Good Morning!

Our photographer here in the Napa Valley (Robert M. Bruno Photography)
has used our product for about 17 years in his darkroom. The only
molecules in our can are inert nitrogen, carbon dioxide and argon...

You should always start with fresh bottles, as nothing will reverse the
oxidation process.

Regards,
Scott Farmer

ps- We have had wine opened, and preserved with "PP" for as long as 4 1/2
years."

 

[Flotsam]

Thanks Shmoo,
Long ago, in another thread I wondered about using products that are meant to displace air in wine bottles for photo chems. It apears that the only consideration might possibly be expense.

 

[b.e.wilson]

Thanks Shmoo,
Long ago, in another thread I wondered about using products that are meant to displace air in wine bottles for photo chems. It apears that the only consideration might possibly be expense.

...and pH.

I've said it before in this thread, but it doesn't seem to be taking, so here's the acid-base chemistry of carbon dioxide:

CO2 dissolves in water to form carbonic acid (CO2 + H2O = H2CO3).

Carbonic acid reacts with any base to neutralize the base if the pH of the solution is higher (more basic than) 5.6, which it is for most developers.

Once the neutralization has happened, the concentration of carbonic acid drops, so more CO2 dissolves, neutralizing more base, lowering the carbonic acid concentration, so more CO2 dissolves.

This process continues until one of two things happens: either all the base is neutralized and the pH of the solution is 5.6 or lower, or you run out of CO2 gas above the solution. The latter is more likely, since there are fewer molecules in a gas than in solution.

So, during the dissolving/neutralization cycle, the pressure of the gas over the solution is dropping. What happens when it drops below the ambient pressure? Any leak will inspire air, thus oxygen. In the end you have only delayed the problem you have when storing a developer with air: the oxygen in the trapped air reacts with the develper, leaving a vacuum over the solution that will then draw in more air.

If you want to preserve a developer (and what else would you want to preserve?) don't use CO2. With the exception, as I've mentioned, of ascorbic acid; it isn't a basic solution and won't react with carbonic acid.

Concerning the statement by the wine protectant company, I can make only two things of it: either it's a lie, or the amount on CO2 is so low that it has no effect on the solution pH. I'd like to believe tha latter.

 

[dr bob]

...and pH.
> lot of cutting here<
Concerning the statement by the wine protectant company, I can make only two things of it: either it's a lie, or the amount on CO2 is so low that it has no effect on the solution pH. I'd like to believe tha latter.

I believe you have it correct. We use a similar technique and material(s) in removing CO2 from submarine atmosphere. As far as the wine industry: my memory (such as it is) says that CO2 is a natural by-product of fermentation. I know that my wine making apparatus used a water seal (bubble) to vent the gas. You can tell when the reaction is “complete” when the bubbles slow down. So I guess that industrial wine comes out pretty much saturated with CO2 so a little added to the void area wouldn’t hurt.

Agree: using CO2 around developer(s) is NOT recommended.

 

[Jorge Oliveira]

Carbon dioxide will react with a basic solution (which most developers are) very quicky to neutralize it. Avoid CO2 at all costs. It will react and leave a negative pressure in the bottle, which will suck air in.

Might be OK for ascorbic acid developers, though.

Ascorbic acid devs (Xtol and the like) are alkaline, as any other devs.
Could you pls elaborate on why would it be Ok to use CO2 with them?

Thanks,

Jorge O

 

[Flotsam]

Thanks to the informed discussion here this has been a very a helpful thread.
I was not educated enough to understand why using inert gas to displace air in a wine bottle would differ from doing the same thing in a developer bottle. The discussion of CO2 has been fascinating.

Thanks to all who took the time to contribute.

 

[b.e.wilson]

Ascorbic acid devs (Xtol and the like) are alkaline, as any other devs.
Could you pls elaborate on why would it be Ok to use CO2 with them?

Thanks,

Jorge O

Being a color man, I haven't used ascorbic acid developers, and wasn't aware they were alkaline.

CO2 will lower the pH, then.

 

[removed account4]

ed -

you can probably get argon at a place that sells welding gas - the same places that sell tanks of helium. you could also find a sign company that does neon & cold cathode work. argon, one of the non-reactive "noble gases" ( its outer shell of electrons is full so it will not react with anything else ) is used like neon & other gases and sometimes phosphors to make colored lighted signs. neon (gas) without any phosphor additives has the characteristic color of red and the sign makers usually add a tiny bit of argon to it to make it electrify brighter. argon can also be used alone like neon (gas) and it has a characteristic color of blue.

http://www.sign-makers.com/listings/USA/MA.html
has a listing of sign-a-rama and they are in danvers & tewksbury ... if you are still looking for a tank of argon, you might give them a call

good luck!
john

 

[Ed Sukach]

ed -

you can probably get argon at a place that sells welding gas -

Thanks, John,

I'm still searching for a source of argon, or other inert gases ... so I'll give them a shot.

Meanwhile ... I've been displacing air with butane from a BernzoMatic mini-torch, and it seems to be working quite well. I have some Tetenal C41 chemicals treated this way about two month and a half ago ... I'll process a roll of AgfaColor - and I'll let everyone here know what the results are.