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Thread: Chemistry 101

  1. #71
    K-G
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    Quote Originally Posted by OzJohn View Post
    Didn't old time chemists call a mixture of nitric and hydrofluoric acids Aqua Regis because it reputedly was the only thing that could dissolve the noble metals? Not being a chemist I'm unsure what glacial acetic acid contributes to the power of this combination but I can certainly vouch for its corrosive powers on skin. I was not aware that it is flammable - you live and learn. OzJohn
    I think what you refer to is a mixture of nitric acid and hydrochloric acid or just sodium chloride ( normal cooking salt ) added to nitric acid. As long as you get the chloride ions into the nitric acid it works.

    Karl-Gustaf
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    Quote Originally Posted by OzJohn View Post
    Didn't old time chemists call a mixture of nitric and hydrofluoric acids Aqua Regis because it reputedly was the only thing that could dissolve the noble metals? Not being a chemist I'm unsure what glacial acetic acid contributes to the power of this combination but I can certainly vouch for its corrosive powers on skin. I was not aware that it is flammable - you live and learn. OzJohn
    That's nitric acid and hydrochloric acid. Nice combination.

    There is this one awesome example of it, being used to dissolve physcicist's gold nobel prizes, sparing it from a nazi raid during the war, the gold was precipitated out later and recast and presented to the physicists again.

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    As others have pointed out, the basic chemistry for B&W is pretty safe when common sense is used. But some photographers eventually begin to delve into the "dark arts" of mixing their own chemistry which involves working with raw compounds that can cause problems if not treated with respect. if one reads the MSDS for catechol (http://fscimage.fishersci.com/msds/04360.htm) you might just run, not walk away even though it is a compound in one of the best film developers you can make from scratch or from a kit.

    As you move into the various realms of alternative processes, you begin to work with various carcinogenic compounds and heavy metals. Wet plate collodion uses a bunch of potentially harmful chemicals from cadmium, to silver nitrate to KCN yet it is one of the most rewarding of all photographic processes. The key is to treat all chemistry with respect and research any new process thoroughly with regards to the handling of chemicals.
    "Fundamentally I think we need to rediscover a non-ironic world"
    Robert Adams

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    Quote Originally Posted by ChristopherCoy View Post
    In a basic darkroom, what is the danger level? What could possibly happen?

    For instance, I've got three chemicals - Dektol, Kodak indicator stop bath, and Fixer. How harmful are those chemicals really? (other than ingestion or eye splashes?)

    Is Dektol going to eat through the skin? Countertop? Will the combo of Fixer and Dektol create a toxic gas?

    Its awesome that you put out a public warning as a chemistry teacher, but for those of use who are absolutely NOT interested in studying chemistry, WHY is safety important? What kinds of accidents are possible with basic chemicals?
    Even the simple darkroom can be dangerous if you are careless. Packaged chemicals, used as directed, are reasonably safe. But even they can react with other things around the house to cause trouble. If you brew you own, you need to be more careful. There are several chemical incompatibilities that you need to be aware of because they can cause serious safety problems. Anschell and Troop's "The Film Developing Cookbook" gives some good guidelines and lists the more common chemical incompatibilities, as do several other photo darkroom books. Even something as simple as pouring developer into fixer can release a cloud of choking, dangerous ammonia gas. Concentrated or solid chemicals are usually more hazardous and generally more troublesome than the diluted solutions. Clean up spills thoroughly and promptly.

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    PE: HF is kept in an HDPE bottle. Sorry to hear about your she-friend's itch

  6. #76
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    lol, I mix developers together all the time. OSHA would love meeeee.
    - Derek
    [ Insert meaningless camera listing here ]

  7. #77

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    Nitric + hydrofluoric doens't make aqua regia as pointed out above.

    But when I worked in an analytical testing lab I once recieved a bottle of nitric and hydrofluoric for testing from a chrome plating shop - it was a pickling bath solution. The liquid in the bottle was dark green and weighted much more than the same amount of water (or those two acids) whould have from all the dissolved metals in it.

    The outside of the bottle was labelled "MF Acid". I showed it around to some of the old timeres there and asked if MF acid was some sort of special industry name they had heard about before - none of them had. But every one of them suggested that is stood for "motherf***en" acid.

    I tested it and it was 35% Nitric, and 10% HF. I think I'd call it MF acid as well if I worked with that on a routine basis...
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

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