Monday, August 17, 2015

Mixed fixer, Potassium & Sodium Thiosulfates


100 g Potassium Metabisulfite
36 g Sodium Hydroxide
29 g Sulfur


First dissolve separately the Metabisulfite and Hydroxide, each in about 500 ml water. Then pour the Hydroxide solution on the Metabisulfite. In this step you are preparing a mix of Potassium and Sodium Sulfites, according to:

K2S2O5 + 2 NaOH = K2SO3 + Na2SO3 + H2O

Bring this 1 liter solution to the fire and when it starts boiling lower the flame and add the 29 g of Sulfur. Let it boil slowly and stir. At a certain point the Sulfur sinks to the bottom. Wait some more minutes and then switch off the fire. Let it cool and filter the solution with coffee filter. Not all Sulfur reacts, but you will end with Potassium and Sodium Thiosulfate and the remaining unreacted Sulfites.

If all Sulfites had reacted the overall reaction would be:

K2S2O5 + 2 NaOH + 2 S = K2S2O3 + Na2S2O3 + H2O


Use the solution you got, about 700-800 ml, undiluted. It takes 5 minutes to fix the normal grain films and 15 minutes the T grain films.


Robert W. said...

Wow, interesting!

Henrique Sousa said...

:-D! One of my mad experiences!