Quote Originally Posted by Michael R 1974 View Post
Isn't it Sodium Bisulphite (Bisulfite) in D-25?
Depends which company publishes the formula, EK use Bisulphite, Kodak Ltd Metabisulphite. it more about the purity of the Meatbisulphite it seems to be manufactured differently in Europe, Kodak Bisulphite is a lower grade mixture of Bisulphite and Metabisulphite.

In some formula the differences are not so important but as a preservative then it becomes more critical.

I used Metabisulphite industrially and there was a significant difference, JT Baker produce and sell both, and the usage depends on how strong an anti oxidant is needed.