Re: Sodium Bisulfite question
s carl king (sanking@hubcap.clemson.edu)
Thu, 18 Jan 1996 14:23:01 -0500 (EST)
>
> The formula contains a small amount of sodium bisulfite, and about that
> Dignan writes: "The Sodium Bisulfite is in the formula only to lower
> the pH to 7 - 7.5 to prevent softening the emulsion of film. If papers
> are to be used, leave out the Bisulfite to deliberately get more
> softening..."
>
> Now, my question is:
>
> 1) Is the above statement correct? (I've confirmed from other sources
> that sodium bisulfite does indeed lower the pH of a solution, but what
> about the "preventing softening"?)
>
> 2) If the statement is correct, then how is my inference that sodium
> bisulfite is a hardener incorrect.
>
I am one of the persons who along with Nadeau wrote that sodium bisulfite
would soften gelatin.
Not being a chemist I have no idea if what Dignan writes is correct or
not within the context. However, I have read in several sources that
sodium bisulfite "by itself" is not a hardener, and it is used
in place of alum in the Kodak F-24 non-hardening fixer.
And I know from experience that if used on carbon and carbro reliefs
while they are still wet, after warm water development, the
reliefs become very soft and are apt to frill.
Perhaps someone who know more about chemistry could shed some
light on this question.
Sandy King