Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,492   Posts: 1,542,972   Online: 890
      
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 24
  1. #11

    Join Date
    Sep 2004
    Location
    Toronto, Canada
    Shooter
    Multi Format
    Posts
    587
    The vapours from concentrated H2SO4 will chemically damage certain materials placed nearby -- I'm pretty sure of that.

    The main danger with H2SO4, besides the burns, is its highly exothermic dissolution in water (which is why we add it to water -- which absorbs the heat and prevents spattering -- and not vice-versa). Your mixing container could become literally too hot to hold. Same goes for when you clean out your measuring containers.

    For my B&W reversal needs I've been using a bleach composed of 65 g/L sodium bisulfate (pH Minus swimming-pool additive) and 10 g/L potassium dichromate. This is an efficient, stable bleach that (when fresh) does its work in well under two minutes.

    I am a practicing chemist and wouldn't want to handle concentrated sulfuric acid outside of a fume hood (i.e. at home). Dichromates are nasty too, but since they are crystalline, inhalation/ingestion is not much of a risk (when they are handled carefully).

    Your clearing bath should be composed of sodium sulfite (I use a 5% aqueous sodium sulfite solution). Metabisulfite clearing baths are used after permanganate bleaches and are not recommended for use after dichromate bleaches (I'm not 100% sure why, I have to review the chemistry of them.) After it's been used once, I find that the metabisulfite clearing baths develop a rather nasty sharp SO2 odour -- another reason to avoid them.

    Any small spills of dichromate bleach can be neutralized before clean-up by treating them with a little bit of your clearing bath, which will reduce the Cr(VI) to the much less toxic Cr(III) and Cr(II).

  2. #12
    Struan Gray's Avatar
    Join Date
    Nov 2004
    Location
    Lund, Sweden
    Shooter
    Multi Format
    Posts
    914
    Just to be clear: my comment in the dichromate was motivated by Swedish environmental laws. Discharging Chromium ions in any oxidation state is illegal. Any large town will have a place you can send your collected waste, usually for free, but I don't know where that is in Göteborg. You just need to find the right 'gubbe' to ask.

    FWIW, I am a physicist, was a Docent at Lund University and for many years was the Safety Officer for my Department.

  3. #13

    Join Date
    Sep 2005
    Location
    Göteborg, Sweden
    Shooter
    Multi Format
    Posts
    558
    Images
    4
    Thank you everyone. It seems there are different views on the sulphuric acid.

    Jordan,
    have you checked out the Negatives by reversal article on unblinkingeye? Would you say I'm at risk of getting hot containers when mixing 50 ml of sulphric acid into 700 ml of distilled water? Should I start with very cold water? I can easily lower the temperature to 5°C or so, as it's winter here.

    Some posters said I could wash the graduate in running water. From what Jordan writes I think it sounds like a bad idea. Can anyone clear this up?

    All in all, do you recommend me NOT making this reversal bleach, trying something else instead? I have already ordered the chemicals.

    Of course, if I had a lab and a fume hood I would use it. I will do this by the sink in my darkroom, not at home. I will try to be as careful as I possibly can, and not being alone while handling the chemicals. If I mess up someone will be able to help me and/or call the ambulance, but let's not hope for that happening.

  4. #14

    Join Date
    Sep 2005
    Location
    Göteborg, Sweden
    Shooter
    Multi Format
    Posts
    558
    Images
    4
    Quote Originally Posted by Struan Gray
    Just to be clear: my comment in the dichromate was motivated by Swedish environmental laws. Discharging Chromium ions in any oxidation state is illegal. Any large town will have a place you can send your collected waste, usually for free, but I don't know where that is in Göteborg. You just need to find the right 'gubbe' to ask.

    FWIW, I am a physicist, was a Docent at Lund University and for many years was the Safety Officer for my Department.
    I will leave the waste CLEARLY LABELED, at my local miljöstation, where I leave spent fixer etc. To be honest, I will not contact the environmental authorities in this matter as I'm already doing this illegally. I don't have a degree in chemistry, I don't have a lab that follows the very strict regulations of swedish environmental law. Getting a permit for this would most probably be impossible. If I knew someone at Chalmers college I would contact them, but I don't. Or maybe I do... will check out.

  5. #15
    Aggie's Avatar
    Join Date
    Jan 2003
    Location
    So. Utah
    Shooter
    Multi Format
    Posts
    4,925
    Images
    6
    A really cheap source of sulfuric acid is at pool supply stores. It's the acid they use to balance the ph in swimming pools. In other words if you swim in a pool you are swimming in some very dilute acid. In California the last time I bought the acid, it cost me $5 for 2 one gallon jugs. That was in 1999. All you have to do if you want to make sure that it is nuetralized before you dump it is put baking soda in it until it stops fizzing. That was all that was required by law in California before we dumped our acid solutions down the drain after using them in the pickling process for jewelry.
    Non Digital Diva

  6. #16

    Join Date
    Dec 2004
    Location
    Milwaukee, Wi
    Shooter
    35mm
    Posts
    3,242
    Others have given you much better advice than could I. I would add only one thought. If you have Potassium Ferricyanide in your darkroom make very certain that they can not come in contact with each other because the effects could be deadly and the dead would not necessarily include you.
    Claire (Ms Anne Thrope is in the darkroom)

  7. #17

    Join Date
    Sep 2002
    Location
    Tijeras, NM
    Shooter
    Medium Format
    Posts
    1,246
    It's all a matter of degree. It will probably fizzle and spatter a bit, but the quicker you get the water in there the better. I have rinsed graduates in a sink with sulphuric acid on them before. Since the amount is small, and you are wearing goggles and apron, you dont have much to worry about.

    The classic case is when someone adds water to acid, it spatters all over and they drop the container they are working with out of suprise, creating a bigger mess.

    Also in the unlikely event you get conc sulfuric on yourself, DO NOT wash it off. The exotherm will burn you, and when the acid is hot/diluted it will react with your skin more readily. remove contaminated clothing immediatly, and wipe as much of it off of your skin as possible. Then you can rinse with water.

    Once I was working in a plant with a lithium amide salt dissolved in tetrahydrofuran. This stuff would spontaniously inflame. One of my thoughtful coworkers forgot to clear a hose and when I picked it up, a couple cups of this stuff went down the front of my pants.
    I stripped down to my underwear and got under a safety shower in about two seconds. Not fun having to walk back to the locker room naked in the middle of the winter.

    On another occasion one of my coworkers had dumped a barrel of caustic soda beads into a tank to neutralize something. The water was hot and when he tossed them in it boiled and he was soaked, the entire front of his body is covered with ugly scars now.

    It is important to understand the properties of what you are working with and be prepared to deal with situations that come up.

    Quote Originally Posted by timeUnit
    Some posters said I could wash the graduate in running water. From what Jordan writes I think it sounds like a bad idea. Can anyone clear this up?
    art is about managing compromise

  8. #18

    Join Date
    Nov 2004
    Location
    TN, USA
    Shooter
    Multi Format
    Posts
    114
    Images
    4
    I would suggest looking on-line at the MSDS (Material Safety Data Sheets) for more safety information on the chemicals you will be using.

    There are certain reactions that can happen during storage, or if a spill should occur, between some of the chemicals that you are handling. The MSDS can advise safe storage and handling, disposal, and what to do in case of spills, exposure, etc.

    Whenever handling larger quantities of more conc. NaOH or acids PLEASE wear eye protection in the form of goggles. I knew a man working with a face shield with NaOH preparation and somehow a droplet flew up and over his shield and into his eye. The eye was permanently damaged, even with access to an eye wash.

    I would also recommend purchasing a bottle (they come in 500mL for example) of buffered eyewash solution and have it on hand. It's amazing how a little acid or base in the eye can render one completely useless, and if your sink is already occupying an ice-bath, you should have ready access to another clean and buffered water source.

    ~Tammy

  9. #19
    Struan Gray's Avatar
    Join Date
    Nov 2004
    Location
    Lund, Sweden
    Shooter
    Multi Format
    Posts
    914
    Henning, I was surprised at how helpful and ready to be flexible the various environmental health people I came across were. Perhaps it's just Lund, but I would turn to them again if I were doing what you were doing.

    There is no reason you shouldn't use dichromates and strong acids for your own hobbies. I hope I didn't give the impresssion that they should be reserved for august institutions. I wanted more to let you know that there are people who are willing and able to help the serious enthusiast on an informal basis, if only with information.

    FWIW, on the sulphuric acid front, I would happily wash glasswear with a few drops remaining in it under running water. The acid-into-water rule, and recommendations for fume cupboards is for beakers with a reasonable amount of liquid that might be dropped. If you are wearing eye protection, gloves and an apron/labcoat there is no reason not to wash off a few residual drops directly.

  10. #20

    Join Date
    Sep 2004
    Location
    Toronto, Canada
    Shooter
    Multi Format
    Posts
    587
    Henning, as the others have mentioned, the running water isn't a problem. The heat of mixing is really only a big deal when you add water slowly to acid -- if you quickly flood the container with water, the exotherm won't be a big problem. (Don't splash it in your eyes!)

    I agree with avandesande that the best thing is to imagine anything that could go wrong, and to prepare ahead for it (make a plan)... and that lithium amide story is pretty sad. I can't imagine working with it on a plant scale. A few grams at a time is fine.

    Once I was doing a trans-metalation reaction at -78C using tert-butyllithium. It ended up precipitating during the addition, and the re-dissolution as the reaction warmed up was VERY EXOTHERMIC... not a pretty sight.

    Don't be too scared of sulfuric acid -- use your head and you'll be fine -- but if you can find "pH Minus" or another swimming-pool-supply source of sodium bisulfate, it'll be much more convenient.

Page 2 of 3 FirstFirst 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin