Replacing Sulfuric Acid

[Photo Engineer]

Sulfuric acid is not generic if you wish to lower the pH. Acetate and Sulfate have entirely different actions in solutions used for photography, and their ability to acidify is different. Sulfuric is a strong acid and Acetic is a weak acid.

PE

 

[fdonadio]

Sulfuric acid is not generic if you wish to lower the pH. Acetate and Sulfate have entirely different actions in solutions used for photography, and their ability to acidify is different. Sulfuric is a strong acid and Acetic is a weak acid.

A really important detail that I'd let pass...

 

[Photo Engineer]

Yes, just as a comment, enough Sulfuric Acid will decrease swell and neutralize base but Acetic Acid has no effect on swell and neutralizes base much more slowly and generally to a less acidic pH mole per mole.

PE

 

[falotico]

I thought H2SO4 might be more efficient when processing thousands of feet of film. I haven't studied the motion picture processing formulas, but I can guess that they do vary from small batch processing.

 

[Athiril]

Sodium Bisulphate works just as well, I've used it, and concentrated sulphuric acid, though I stick to dichromate bleaches for reliability.

 

[mrred]

But it doesn't last. I took a year off doing reversals and my batch of Sodium Bisulphate mix didn't work anymore. It took a while to pinpoint what it was. I still have 10 litres of %20 Sulfuric Acid so I just moved on.

 

[Tom Taylor]

Could anyone tell me how 2 ppm Iron would improve safety of concentrated Sulfuric Acid?

That's a very good question - one that I also asked. The only reason that I can think of is that the iron discolors SA rendering it more visible. My copy of Harley's Condensed Chemical Dictionary 1987) describes its proprieties "Stongly corrosive, dense, oily liquid; colorless to dark brown depending on purity..."

I found another vendor that sells a 98% clear concentration without the iron but at triple the price. Somewhere I read that minute quantities of metal will cause the SA to discolor.

Thomas

 

[Rudeofus]

I wonder whether 2 ppm Iron in Sulfuric Acid effectively prevent making of Piranha Solution, since the Iron would kill the Hydrogen Peroxide in no time ... so it may not be "safety of regular use", but "safety of others from idiots who try to make nasty stuff" that's causing the price difference.