dichromate reaction products / fumes

Discussion in 'B&W: Film, Paper, Chemistry' started by johnielvis, Oct 19, 2011.

  1. johnielvis

    johnielvis Member

    Messages:
    940
    Joined:
    May 21, 2010
    Shooter:
    Medium Format
    OK--when I was doing small sheets and rolls in a tank, I'd occassionally get a little ozone type whiff.....not much and not long.

    now I"m doing 11x14 reversals and tray-bleaching---lemme tell you...there's a HUGE reaction area with this.....so now...the reaction fumes are more "noticable" .... and it smells different now....maybe it's the different bleach I"m using..I was using kodak dichromate motion picture bleach liquid concentrate--just ran out...now I'm using dichromate mixed with sodium bisulfate instead of sulphuric---SO---the smell is actually a mix of the ozon-y smell along with this other smell that smell like this old agfa paper I have--NOW---what are the possible reaction products of dicrromate bleaching of film--I know it should be just like ozone at the worst- but now I'm afraid I'm getting like welding gasses--chromic oxide stuff---is that possible? or am I maybe also smelling some of the acid too--this is the first time I'm using the "homebrew" bleach.....

    I've heard that the dichromate will react with the gelatain to harden it, so is there something coming out there? I'm only concerned if it's BAD stuff that can be getting evolved---it doesn't look like chromium getting evolved can be a concern--looking at the reaction, but...maybe it IS???? anybody know for sure what the OTHER byproducts are?

    I'm now just going to abaondon the tray bleaching for sure and do it all in tubes to keep the stuff more confined and away from me...besides the tubes agitate better.....hopefully the tubes will considerably reduce the fume problem BUT STILL!!!!! any idea if chromium fumes are a concern, or is that just not very likely from a chemistry perspective?
     
  2. holmburgers

    holmburgers Member

    Messages:
    4,423
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Unfortunately I don't have a useful answer, just a useless anecdote.

    It's very interesting you mention ozone. Thomas Manly invented the "Ozobrome" process which required a dichromate bleaching step and was a precursor to the carbro process (as I understand it). It's called ozobrome specifically because he believed that ozone was being released. (though elsewhere I may have read that this wasn't totally accurate).

    How 'bout that?
     
  3. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,773
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Are you sure you are using BisulfATE? Is it pure?

    Please change to Dichromate in Sulfuric acid. That should reduce odor substantially.

    The reaction is Ag metal being oxidized by Dichromate to Silver ion which reacts with Sulfate and it dissolves. The Dichromateis reduced. There should be no gasses released and any reaction with gelatin does not release gas.

    PE
     
  4. johnielvis

    johnielvis Member

    Messages:
    940
    Joined:
    May 21, 2010
    Shooter:
    Medium Format
    Whew!!!! thanks.....that makes me feel a bit better...YES..the sludge production is WAY up now that I'm using bisulfate for acid (dry acid)...I got it from pool supply outfit, so there's gonna be some impurities I'm thinking....but it sure works good.....iFrom your answer I'm thinking that any impurities from the bisulfate batch (pool grade) will also not react with the chromium to produce volatile chromium fumes, right?

    ON the gas evolution, I did read in some photo chem book...gotta re-dig it up, that there is oxygen/ozone created in the reaction....maybe i remember it wrong...or maybe I'm just thinking that's what i read due to the "ozone smell" that I seem to be getting--but I always got the "ozone smell" even when I used the clean kodak liquid---that stuff was pot dichromate and a combo of sulfamic and sulphuric acid...it was produced maybe 15 years ago by kodak motion pictures division---reversal bleach concentrate and replenisher----VERY good stuff....anyways...I just used up the 15 gallons yesterday...and now they dont' make it anymore--they make the permanganate substitute...I think I'm going to buy that and try it out since the permanganate is comparatively safer---peace of mind.....you know?
     
  5. john_s

    john_s Subscriber

    Messages:
    1,103
    Joined:
    Nov 19, 2002
    Location:
    Melbourne, A
    Shooter:
    Medium Format
    Pool chemicals don't have to be very pure. Although it wasn't a chemical relevant to your problem, one pool chemical I bought claimed "83% purity." No mention of what the other 17% was.
     
  6. Gerald C Koch

    Gerald C Koch Member

    Messages:
    6,242
    Joined:
    Jul 12, 2010
    Location:
    Southern USA
    Shooter:
    Multi Format
    Potassium dichromate is not going to produces any "chromium fumes." I suspect that what you are smelling is a small amount of chlorine gas. Any chloride ion present can be oxxidized to chlorine by the dichromate.
     
  7. johnielvis

    johnielvis Member

    Messages:
    940
    Joined:
    May 21, 2010
    Shooter:
    Medium Format
    chlorine....well---it maybe that was part of the "other smell" that I"m smelling...I guess it could be a little chlorine smelling...or maybe that ozone smell is actually chlorine? that could be--they both do the same thing, right? plus, I never smelled chlorine gas....only hypochlorite bleach, which may or may not smell like the real nasty nasty chlorine....or cut with oxygen, maybe that's what it smells like...or maybe the chlorine somehow makes o2 into o3 as it evolves?...

    NOTE I never see any bubbles at all...this is all like gas diffusing up from the liquid surface...no bubbles ever.

    and another big thanks...I was getting so worried that a took a whiff and now I'm doomed....but, good to get some verification that whatever it is, it's not chromium.....