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Thread: Chemistry

  1. #41
    Ole
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    Ed, Jorge...

    Unless you store your chemicals in barrels, a fraction of a second is more than enough.

    I don't know the throughput of Ed's MiniTorch, but if the level drops visibly you have used far too much!

    Butane is reasonably safe, but not when you use enough to get a whole room up to Lower Explosive Limit (about 5%, IIRC)!

    Jorge, how much gas will result from the liquid that passes through the nozzle in a second? !0 seconds at full blast will give you about a cubic meter, which is a serious amount of potentially explosive gas to let loose in a darkroom.

    With a gas lighter a few seconds is correct. But a butane refill flasks fills a lighter in seconds, which in turn gives nice steady flame for HOURS, not seconds!

    It takes more than a few seconds to see a visible change in the level in a lighter, which I guess is much smaller than Ed's Mini-Torch.

    You are using way too much gas!
    -- Ole Tjugen, Luddite Elitist
    Norway

  2. #42
    Ole
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    All right, panic over:

    1 mol of butane weighs 58g, and will fill a volume of 22.4 liter at "standard lab temperature". Since liquid butane has a specific gravity of about 0.8, that gives about 0.3 liter (300 ml) per cubic centimeter of liquid gas. The Lower Explosive Limit of Butane is 1.6%, the Upper limit is 8.4% (I checked).

    So one cc of lighter gas can make an explosive volume of (0.3/1.6)x100 or 18.75 liter. Less than a darkroom-full, but a lot more than a bottle!

    Anyway: Butane is heavy enough to form a "gas blanket" covering the bottom of the airspace, so you don't need (or even want) to fill the entire volume with gas.

    You're still using way too much, and my initial guess of "a few secons with a disposablegas lighter" is basically correct. A few seconds with a similar volume of liquid butane is way too much. If you need more than 300ml to top off your bottle, find a smaller one!


    See for example http://info.anu.edu.au/hr/OHS/Hazard...rs_In_Labs.pdf for some information on gas and hazards in closed spaces.
    -- Ole Tjugen, Luddite Elitist
    Norway

  3. #43
    Jorge Oliveira's Avatar
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    Ole

    Thanks for the warning.

    First, my 'a few seconds' is more like 1~2 sec.

    I have weighted the bottle before and after a pour, spraying the gas out of the window.

    My pour was 2 grams. Nice cloud, BTW.

    I started using it in a shorter pour, but was under the impression that it was too little (plastic botlle still 'bulging inside' - forgot that word again!).

    What do you think?

    Jorge O

  4. #44
    Jorge Oliveira's Avatar
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    Ole

    Just a note - my darkroom is in the bathroom, and the chemicals (and where I use butane) are kept in the laundry - a ventilated place.

    Jorge O

  5. #45
    Ole
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    Ventilation is always a good idea. What I'm worried about is an expanding cloud of butane - there is always explosive mixture on the edge of such a cloud until the whole thing is diluted enough.

    Do you mean that the plastic bottle is contracting when closed tightly and left for a while?
    If so, that could be for a number of reasons: Change in temperature, change in air pressure, air or butane dissolving in the liquid... If you blast enough gas into it to cool it down significantly, it will bulge as it warms up. That doesn't necessarily mean that the liquid isn't absorbing gas, though...

    With the "whoosh" coming out of those refill bottles, it is difficult to get all of it to stay inside the "target" bottle. It is a lot easier with a slower rate, as from a lighter. See if you can find a cheap refillable - even a broken one which won't light. useful in a darkroom, useless to smokers

    I'm probably a bit paranoid from working in the oil/gas industy for 13 years, but we take gas leaks very, very seriously here.

    An "interesting" experiment to illustrate my point: Take a spray bottle of just about anything. Deodorant and hairspray are particularly impressive. Take it outside, bring a candle. Light candle. Spray just past the flame, being careful not to blow it out.
    Then wait for eyebrows to regrow
    -- Ole Tjugen, Luddite Elitist
    Norway

  6. #46
    jbj
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    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.

    Correct me if I am wrong but I fail to see the logic behind spraying any gas or ‘protectant’ only on top of the solution. If you could bubble butane through the solution for a while this would work. But spraying it on top of the solution would only prevent more air/oxygen from entering the solution. And this would probably only occur if you sprayed a light stream in the headspace of the bottle for some time, not just a few quick spurts. This is the same phenomenon with using marbles. Clearly the problem is that the dissolved oxygen will still remain in solution. Oxidation still occurs.

    It would be interesting to do an experiment to determine the best method, see if some of these methods actually work, and compare the effectiveness of the many that have been shared.

    My method: I bubble argon through the solution while stirring on a stir plate for a couple minutes. I then attach a rubber septum to the bottle and flush the headspace with argon. This works great with D76 stock solution/ Dektol/ Fixer, etc. This may be overkill for photographic solutions, but for my real job in the laboratory it is appropriate and I can tell the difference.

    Enough rambling...hope this makes sense. Good night!

  7. #47
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    I'm just looking to displace the air in the headroom of the partially full bottles or at least float a layer of heavier inert gas on the solution surface as a barrier. Trying to drive all the oxygen from within the solution is way above and beyond the mission.

    Maybe the best low tech answer is those accordian bottles or a bladder container.
    That is called grain. It is supposed to be there.
    =Neal W.=

  8. #48
    uma
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    in my lab,i use plastic or acralic lids floating on the solution and it helps to some extent to reduce direct contact of tank solution with air
    and it is extremely cost effective

  9. #49
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    uma,
    Exactly. Unfortunately that isn't a viable answer for the 500ml and liter bottles that the home darkroom user often needs to protect.
    That is called grain. It is supposed to be there.
    =Neal W.=

  10. #50
    Ole
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    I typed a long comment on the stability of different chemistry mixes and the necessity of protecting them, but then I lost it!

    My (tentative) conclusion is:

    Most stock solutions last for a long time without protection.

    Most work solutions don't.

    Fixer lasts - I routinely leave mine for several weeks, then carry on where I left off.

    My brown plastic bottles are never full, yet the chemicals don't "rot" while I'm away for two weeks.

    I don't know anything about colour chemistry.
    -- Ole Tjugen, Luddite Elitist
    Norway

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