[pure-silver] Re: Adding Sodium Sulfite to Sodium Thiosufale.
- From: Gerald Koch <gerald.koch@xxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 2 Apr 2011 19:21:30 -0700 (PDT)
Aerial oxidation of thiosulfate is very slow in the absense of a catalyst. A
plain hypo bath should last for many months. Sodium thiosulfate solutions are
used in analytical chemistry. If they were unstable to air then they would be
unsuitable for that purpose.
Jerry
________________________________
From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
To: pure-silver@xxxxxxxxxxxxx
Sent: Sat, April 2, 2011 7:10:01 PM
Subject: [pure-silver] Re: Adding Sodium Sulfite to Sodium Thiosufale.
----- Original Message ----- From: "Gerald Koch" <gerald.koch@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Saturday, April 02, 2011 3:29 PM
Subject: [pure-silver] Re: Adding Sodium Sulfite to Sodium Thiosufale.
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
The sulfite will also tend to preserve the thiosulfate from oxidation from
the
air. A common non-hardening fixing bath will have about 5 grams/liter of
sulfite
in it. The usual acid bath has about 15 grams per liter. The small amount of
sulfite also prevents staining from carried over developer, which in a non-acid
bath, may remain active for a time.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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