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  1. #1

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    Sulphuric acid substitute

    I'm a newbie on this forum so please don't shoot my back... :-)
    I've got the following question: is there a substitute for sulphuric acid in the b&w reversal process, and if yes, what quantity or concentration?
    Thanks in advance.

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    Quote Originally Posted by Alessandro Serrao
    I've got the following question: is there a substitute for sulphuric acid in the b&w reversal process, and if yes, what quantity or concentration?
    Thanks in advance.
    The reversal step needs quite a strong acid, most recipes I remember are 10-15 ml of sulfuric acid, of course if you are more comfortable you can use diluted sulfuric acid in a higher amount.
    I could not find the source but I think you might be able replace it with either the sodium hydrogen sulfate or potassium hydrogen sulfate, roughly three times the weight. Maybe it was Maco or Foma reversal formula.

    To be honest I would recommend to use the acid and just be careful, battery acid is sulfuric acid.

    Regards,

    Wolfram
    Colour? We can always use an airbrush later...

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    Go read http://unblinkingeye.com/Articles/NbyR/nbyr.html

    He recommends Permanganate Reversal Bleach.

    There was a thread on permanganate recently on apug.

    Best,

    William
    "I know of no country in which there is so little independence of mind and real freedom of discussion as in America." -- Alexis de Tocqueville

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    Quote Originally Posted by Alessandro Serrao
    I'm a newbie on this forum so please don't shoot my back... :-)
    I've got the following question: is there a substitute for sulphuric acid in the b&w reversal process, and if yes, what quantity or concentration?
    Thanks in advance.
    Yup -- Sodium bisulfate, also known as sodium hydrogen sulfate (do not confuse with sodium bisulfite) dissolves readily in water to produce a very acidic solution equivalent to dissolving both sodium sulfate and sulfuric acid in water.

    I've been using "pH Minus" pool additive, which is at least 95% sodium bisulfate (the balance being probably sodium sulfate) for a home reversal process and it seems to work fine. I am having a bit of a problem with over-bleaching, though.

    E-mail me if you need more details.

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    Quote Originally Posted by Jordan
    Yup -- Sodium bisulfate, also known as sodium hydrogen sulfate (do not confuse with sodium bisulfite) dissolves readily in water to produce a very acidic solution equivalent to dissolving both sodium sulfate and sulfuric acid in water.

    I've been using "pH Minus" pool additive, which is at least 95% sodium bisulfate (the balance being probably sodium sulfate) for a home reversal process and it seems to work fine. I am having a bit of a problem with over-bleaching, though.

    E-mail me if you need more details.
    Can I use potassium alum sulphate in substitution of sulphuric acid?
    Can I use the alum as a hardener as well?

  6. #6
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    Slightly off thread but I cannot get Sulphuric Acid in concentrations of greater than 10%. Whilst I am happy to use 10x the amount when a formula calls for concentrated Sulphuric Acid is Sodium Bisulphate a universal replacement for Sulphuric Acid?

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    Quote Originally Posted by Alessandro Serrao
    Can I use potassium alum sulphate in substitution of sulphuric acid?
    Can I use the alum as a hardener as well?
    Potassium aluminum sulfate solutions are probably weakly acidic but not nearly enough to acidify a bleach. The reason why sodium bisulfate (sodium hydrogen sulfate) can replace sulfuric acid is because it is an 'acid salt' of sulfuric acid -- sulfuric acid partially neutralized with base, as it were. When sodium bisulfate is dissolved in water, it forms a solution that is identical in composition to one produced by dissolving both sulfuric acid and sodium sulfate in solution in equal concentrations.

    I wouldn't want to experiment with mixing alum with a bleach. The results could be very unpredictable or dangerous.

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    Quote Originally Posted by Adrian Twiss
    Slightly off thread but I cannot get Sulphuric Acid in concentrations of greater than 10%. Whilst I am happy to use 10x the amount when a formula calls for concentrated Sulphuric Acid is Sodium Bisulphate a universal replacement for Sulphuric Acid?
    It can replace it in many formulas. As I mentioned in the previous post, when you dissolve sodium bisulfate in water it creates a solution equivalent to one created when equimolar amounts of sulfuric acid and sodium sulfate are present. If this sodium sulfate doesn't interfere in your application, you should be fine.

    Any more questions, just let me know.

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    Quote Originally Posted by Jordan
    It can replace it in many formulas. As I mentioned in the previous post, when you dissolve sodium bisulfate in water it creates a solution equivalent to one created when equimolar amounts of sulfuric acid and sodium sulfate are present. If this sodium sulfate doesn't interfere in your application, you should be fine.

    Any more questions, just let me know.
    Actually, the more I think about it, the more I realise that what I wrote above is not strictly true -- that the sodium bisulfate solution is equivalent in action to an equimolar mixture of sodium sulfate and sulfuric acid. It is probably equivalent to something other than a 1:1 mixture. In any case, the sodium bisulfate can successfully be used to acidify a bleach and for some other photographic purposes.

  10. #10
    Ole
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    Jordan, you were right the first time: One mol of sodium sulfate plus one mol of sulfuric acid = 2 mol of sodium bisulfate. If I knew how to make subscripts in this system I'd write it out properly.

    This mixture will never get the pH as low as "real" sulfuric acid will, but it might be enough.

    And by the way: "Bisulfate" means a salt of a metal, hydrogen and sulfate, like NaHSO4. Sulfate has no acid hydrogen, like Na2SO4. Sulfuric acid is H2SO4.

    Sulfates without hydrogen are alkaline, and can not be used as a substitute for an acid. But sometimes what you want is the sulfate ions, sometimes the acidity. If it's sulfate you're after, any sulfate will do. If it's acidity, acetic acid will do.

    So it really depends on the application.
    -- Ole Tjugen, Luddite Elitist
    Norway

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