Sodium sulfite is not needed unless that hypo solution is acidified in
some manner. If you don't use an acid stop bath you won't need it.
When acid is added to a sodium thiosulfite solution colloidal sufur is
produced. The sulfite ions combine with the sulfur to regenerate
thiosulfate ions.
There is a classic chemistry demonstration called "the setting sun."
A beam of light from a slide projector is passed through a thiosulfite
solution onto a screen. It looks like the sun. Then, with stirring,
a small amount of acid is added. The "sun" becomes more and more
reddish in appearence as colloidal sulfur scatters the light. It
looks like the sun is setting. This scattering is of course exactly
what happens to the real sun as it reaches the horizon. The light
must pass through more of the atmosphere with greater scattering of
the shorter wavelengths.
Jerry
------------------------------------------------------------------------
*From:* Bogdan <bkarasek@xxxxxxxxxxxx>
*To:* pure-silver@xxxxxxxxxxxxx
*Sent:* Sat, April 2, 2011 5:48:17 PM
*Subject:* [pure-silver] Adding Sodium Sulfite to Sodium Thiosufale.
hi all,
In the discussion on using 2 bath Sodium thiosulfate, someone
mentioned adding Sodium sulfite to prolong the keeping properties of
simple hypo.
I'm using Anchell's "Darkroom Cookbook" as my reference for my chemistry.
For plain hypo, He recommends 480.0 grams of Sodium Thiosulfate per 2
L of water; how much Sodium sulphite should I add to assure longevity.
Till now, I have never added Sodium Sulfite to the hypo and would tone
the prints in 1:9 KRST (no additives) and then wash.
Any suggestions of the amount I should add to the hypo?
Cheers,
bogdan
__________ Information from ESET NOD32 Antivirus, version of virus
signature database 6010 (20110402) __________
The message was checked by ESET NOD32 Antivirus.
http://www.eset.com
