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  1. #1

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    Chemistry question - hydroquinone and ammonium thiosulfate

    I have a couple of questions about common B&W chemicals....

    What is residual hydroquinone and how is it different from hydroquinone? Can either be used to make developers? Are there any conversion necessary if a recipe calls for hydroquinone and I use "residual" type?

    Why is ammonium thiosulfate only available in 60% solution rather than powder?? For example, a recipe in "Way Beyond" book calls for 120 grams of ammonium thiosulfate. It does not say in what hydration. (anhydrous/monohydrate/etc) Many other recipe I've seen is the same way. Is this a convention that I'm not aware of?

    Can someone give me a hand?
    Develop, stop, fix.... wait.... where's my film?

  2. #2
    RalphLambrecht's Avatar
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    i also wish aammonium thiosulfate would be available in powder more readily. howeverit shouldn't be too difficultto calculatehow much of the 60%solution is required to get the same effect as 120gof powder per liter
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  3. #3

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    Ammonium thiosulfate is supplied as a 60% solution because the solid is unstable. 100 g of the solution contains 60 g of ammmonium thiosulfate. To convert this to liquid measure divide by the specific gravity of the solution ~1.33 g/ml.

    I have no idea what "residual" hydroquinone is. Where does this term appear?
    Last edited by Gerald C Koch; 06-22-2012 at 11:28 AM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  4. #4

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    http://www.adorama.com/PYH100G.html

    What exactly does it mean by "unstable?" Is it going to degrade fast or is it "boom!" kind??
    Develop, stop, fix.... wait.... where's my film?

  5. #5
    Ian Grant's Avatar
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    What is Residual Hydroquinone, never heard of it ? If you stick the term into Google it refers to thev Photoformulary and skin lightening

    It should mean the very slight residues of hydroquione left in an emulsion/paper base after processing.

    Ammonium Thiosulphate (cryst) is readily available in Europe it's not so much unstable as hydroscopic so attracts water and tends to end up as a sticky mess, so for commercial use it's usually sold as a solution.

    Ian

  6. #6
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    Maybe the Formulary is calling it 'Residual' because it's coming from the bottom of the drum that they bought it in? Who knows? I bought a 100 gram bottle of Formulary Hydroquinone from Adorama less than a year ago. I don't remember how it was listed at their website, but the bottle is labeled Hydroquinone with no mention of Residual.
    Happiness is a load of bulk chemicals, a handful of recipes, a brick of film and a box of paper. - desertrat

  7. #7

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    While the ammonium ion NH4+ has a chemistry similar to that of sodium and potassium ions this is only true in acid solutions. Thus a salt like ammonium chloride is stable in acid solution but begins to liberate ammonia gas when the pH of the solution gets above 7. When heated the solid dissociates into ammopnia gas and hydrogen chloride. Ammonium bicarbonate is used as a leavening agent beause it decomposes to ammonia, water and carbon dioxide at oven temperatures. Ammonium carbonate is so unstable that it does not exist at all. Solid ammonium thiosulfate slowly releases ammonia even at room temperature. As Ian points out it is also deliquescent absorbing water from the air and liquifying. This is why it is sold as a solution of known composition.

    Speaking about booms, ammonium nitrate makes an excellent explosive and will detonate spontaneously if a large quantity is allowed to become moist. This happened in Texas City in 1947 when a whole shipload (2300 tons) went up taking most of the town with it. At least 581 people were killed.

    I never buy anything from PF as I think their prices are too high and the purity of some their chemicals suspect. I buy developing agents and some other chemicals from www.techcheminc.com.
    Last edited by Gerald C Koch; 06-22-2012 at 02:50 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  8. #8
    eclarke's Avatar
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    Here's a link, youtube video about the explosion.. http://www.youtube.com/watch?v=Tworc...e_gdata_player

  9. #9

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    The problem with ammonium thiosulfate is that it is hygroscopic - it aggressively absorbs water from the air. In a damp environment you may even get puddles of ammonium thiosulfate solution along with the solid material. That means that the problem with the solid is that you can't be sure of just how much you have when you weigh it out, unless you keep it in a desiccator.

  10. #10

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    Understood on ammonium thisulfate....

    Any ideas on Residual hydroquinone? Googling is the first thing I did and I, too, found all kinds of references to making some kind of creme. So I take it, this is not a proper or even common chemical name.... Very strange.
    Develop, stop, fix.... wait.... where's my film?

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