Thanks for noticing....Actually after your 1st post I went to a book
called "Photographic Chemicals and Chemistry" by Southworth & Bentley,
3rd edition, 1957, & found this entry:
Sodium Bisulphite: (Acid Sulphite of soda, sodium hydrogen sulphite.)
NaHSO 3=104. Fine, colourless crystals or powder, having a weak odour of
sulphur dioxide. ... giving a strongly acid solution......Also
supplied commercially in saturated (about 40%) solution, saturated with
sulphur dioxide as "bisulphite lye" or "acid suylphite lye." This may
conveniently be prepared by adding strong sulphuric acid (5 parts) to a
saturated solution of normal sodium sulphite (100 parts). Used as the
acidifying and stain-preventing constitutent of acid-hypo solutions and
(in conjunction with hypo) for removing silver stains from POP prints.
End of quote.
So then I re-read the Puyo & it was now clear that the "ordinary sodium
bisulphite" reference was to an ordinary darkroom, not cleaning
compound. But what was most astonishing was his description of how he
used it for spot clearing and general lightening of a gum print, almost
exactly the way we would "bleach" a print with potassium ferricyanide.
I've never seen mention of such anywhere else...wonder if it works....
We of course use sodium bisulphite for clearing gum prints of residual
dichromate stain. So while the spirit was upon me I checked every source I
could find on that. The only one who mentioned more than "use this or
that" was Scopick, who said,
"sodium metabisulphite and sodium bisulphite ....are not as soluble as
potassium metabisulphite in water and thus require a long wash time."
One must not trust Scopick even should he say grass is green (trust me),
so I checked that -- it wasn't footnoted. Found only one brief solubility
chart in "Elementary Photographic Chemistry, Eastman Kodak, 194l.
This gave solubility at 40 degrees F and 70 degrees F with the explanation
that "a solution is liable to become cooled in winter to a temperature
approximating 40 degrees F." (Good Grief! Did they work outdoors?)
The chart says potassium metabisulfite will dissolve 47 ounces in 100
ounces of water at 40 degrees, 57 ounces at 70 degrees.
For sodium bisulfite, the figure is 52 and 52.
In other words, the metabisulfite is LESS soluble at lower temperature,
only SLIGHTLY more soluble at normal room temp. (My studio is 80 degrees
today, but we won't count that.) The difference of 5 ounces (10%?) seems
But I have a more basic question which, if you're still reading, maybe
some of you chemistry mavens can answer.
The chemical, whichever it is, is already dissolved in water when we use
it. So why would its solubility in water be an issue in the matter of
washing it out? Is there any relation between solubility in water and
readiness to depart paper?
Of course, length of wash after clearing bath is an issue......we're
pretty weary by the time we get to that stage. And we do have a fetish
for "the best"... (perhaps a concept best left to David Letterman).