Sodium Thiosulfate question
This is for the chemist expert. Im going to buy some Sodium Thiosulfate and found two providers with a slightly different formula:
They both say it is good for fixing papers. What is the difference between those? And does it matter?
The pentahydrate (5 H2O) is the familiar one ("hypo") so I would get this; I'm not sure whether the 6 H2O is genuinely different or just a typo by the seller.
Edit: I see they both state they are pentahydrates, so presumably it's a typo. But I'd still be safe and get the one that is correctly identified (5 H2O).
Last edited by andrew.roos; 01-09-2013 at 05:12 AM. Click to view previous post history.
I have contacted the provider for details, the 6 H2O is much cheaper :-) Thank you!
Originally Posted by andrew.roos
definitely there does not exist a sodiumthiosulfate-hexahydrate ( x 6 H2O), only a pentahydrate (x 5 H2O) and the anhydrous form. I'm a chemist and I have read many old and new books about photographic formulations, I never found a hexahydrate. Also in books about inorganic chemistry and in chemical encyclopedias you'll only find the pentahydrate and the anhydrous hypo. This is an error.
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You are right, it was a typing error. The provider have fixed the error :-) I'm pretty impressed by the level of knowledge on this forum. Thank you!
Originally Posted by jochen
Didn't see the listings before the info was updated, but do pay attention to the quantities shipped. One is for 25Kg, the other, although cheaper, is only 5Kg - In terms of Kilo per Euro, the 25Kg listing is better value.
Originally Posted by StigHagen
I will buy the 25kg....that is cheap fixer for sure :-) I will add some Sodium Bisulfite to the first fixer tray (2 bath system).
there is slightly more water of crystallisation in the second product and this will affect a calculation of the weight of product to add to a solution -- I think the x in the first product formulation is just ignorance, throw away the x and reorder the Sulphurs and the Oxygen content. Conventionally the product would be written Na 2 S2 O3 and suitably subscripted...
you make up solutions to add a fixed weight of the thio to a fixed quantity of water
the following solutions are chemically identical
158 g of anhydrous thio sulphate in 1 litre water
248 g of Na2 O3 S2 5H2O
266 g of Na2S2O3 6H2O
having said all that , one of those hydrations is unstable and the product will absorb or lose water to the environment.