Sodium Thiosulfate "Plain Fixer" question

[tgtaylor]

To the above I would add the clarification that you would want to add Sodium Thiosulfate to water and then bring up the resulting solution to the desired volume. For example add 15 grams of ST to less than 100mL of water and then bring it up to 100 mL. Only then will you have a 15% solution - 15gms of ST, 85 gms of water.

Thomas

[atlcruiser]

So my goal is a 15% solution. When I was reading Michaels A Smiths Lodima/Azo techniques he wrote 32oz to 1 gallon that is why I mixed 16oz to 2L. If I go with the 15% solution goal it looks like I made the solution to rich.

thanks

[Lynn Jones]

You'd better have some Na Sulfite in the solution because it regenerates the thiosulfate. Whatever you do, don't use two bath fixation, lots of films have been destroyed by that silliness. It is a common cause of colloidal sulfur contamination. Always use good fixer, properly. Some replenishment is perfectly acceptible.

Frankly, a good rapid fixer with replenishment will last for a very long time and without serious chemical problems.

Lynn

[tgtaylor]

Strike ""- 15 gms of ST, 85 gms of water -" in my post above as the solute also has volume. dissolving 15 grams of ST in water and then adding water to bring the volume up to 100 mL will give you a 15% solution but you will have a little less than 85 grams of water as the solute has volume necessarily greater than 1gm/mL.

Thomas

[BetterSense]

Why could 2-bath fixing possibly cause problems?

[Leigh]

Perhaps I'm missing something, but it seems that...

given the molecular weight of the pentahydrate as 248.18, and
given the molecular weight of water as 18.015,
thus water constitutes over 36% of the pentahydrate by weight, so...

Dissolving 150 gms of the pentahydrate in 1 liter (total volume) of solution would only yield about 10% sodium thiosulfate, the remaining 5% being water contributed by dissolving the crystals.

Yes/no?

- Leigh

[Kirk Keyes]

150 grams of anhydrous sodium thiosulfate would give a 15% w/v solution when dissolved into 1 L of water.

I've never heard of two-bath fixing ever ruining film. In fact, I've been using it for about 20 years now and never had a sheet (or roll) ruined by it - from colloidial sulfer or otherwise.

I recommend two-bath film fixing as a great way to ensure complete fixing.

[Leigh]

150 grams of anhydrous sodium thiosulfate would give a 15% w/v solution when dissolved into 1 L of water.

True, but what's being discussed here is pentahydrate, not anhydrous.

That was the reason for my previous post.

- Leigh

[atlcruiser]

I am strongly in the camp of the 2 fix...it has been done that way for years by many, many folks with no issue especially whwn the sodium bisulfite is added and the fix is swapped. I want to ensure there is nothing left in the paper!

I only do this with FB paper and use rapid fix for all RC papers.

[Kirk Keyes]

True, but what's being discussed here is pentahydrate, not anhydrous.

That was the reason for my previous post.

- Leigh

Interestingly, heylloyd lists "plain hypo fix" as using 160g anhydrous sodium thiosulfate into 1 liter (along with 30-60 g sodium sulfite).
http://www.heylloyd.com/technicl/plain.htm