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!
Ed Sukach, FFP.
Two items of clarification, from a chemist's point of view:
Originally Posted by jbj
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]
i have tried the last option,(printing enough) and it works just fine,
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.
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.
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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.
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.
Originally Posted by Boris
Might be OK for ascorbic acid developers, though.
but i think CO2 will be dissloved with tank solution and increase it 's pH by oxidation.
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!!!
Ed Sukach, FFP.
How would I go about to empirically test this hypothesis?
Originally Posted by uma
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.