Kodak F-24 Fixer Formula

[payral]

Hello,
In The Darkroom Cookbook, Formula #132 Kodak F-24 Nonhardening Acid Fixer say Sodium Thiosulfate 240,0g.
But it doesn't say which Sodium Thiosulfate version:crystalline or anhydrous.
Can you tell me ?

 

[pdeeh]

the formula as given by Kodak in publication J-1 specifies Pentahydrate for the thiosulfate, anhydrous for the sulfites

 

[Gerald C Koch]

While anhydrous sodium thiosulfate is available it is not the stable form. Usually formulas are written to use the most stable forms of a chemical. If this should not be true then the particular hydrate will be specified. When exposed to humid air the anhydrous form of sodium thiosulfate will set to something resembling concrete.

 

[payral]

Thanks for your answers.

 

[jochen]

Hello,
if you have anhydrous sodiumthiosulfate, multiply the amount of the pentahydrate by the factor 0.637, so instead of 240 g pentahydrate take 153 g of the anhydrous salt. Commercially available powder fixer mixtures usually contain the anhydrous thiosulfate as the transport of useless water costs money.

 

[Xmas]

Hello,
if you have anhydrous sodiumthiosulfate, multiply the amount of the pentahydrate by the factor 0.637, so instead of 240 g pentahydrate take 153 g of the anhydrous salt. Commercially available powder fixer mixtures usually contain the anhydrous thiosulfate as the transport of useless water costs money.

To say nothing of pollution of the atmosphere of Planet I with CO2, does any one know where planet II is?

I just use straight hypo more dilute is ok as long as you replace on use more frequently.

 

[Jburns]

While anhydrous sodium thiosulfate is available it is not the stable form. Usually formulas are written to use the most stable forms of a chemical. If this should not be true then the particular hydrate will be specified. When exposed to humid air the anhydrous form of sodium thiosulfate will set to something resembling concrete.

Hi,
I’m mixing up F-24 now. The old 25lb container says Sodium Thiisulfate technical granular. It is hard as a rock but I can break it up with a big screwdriver to weigh it out. Is there any chance it’s not anhydrous? It’s mostly white with areas with some translucency. Is there any negative consequence to using too much sodium thiosulfate? Thanks for any insight!

 

[mshchem]

I don't know what to say. Most of this stuff is supplied as a pentahydrate. Which is usually free flowing crystals. It should have a formula weight or some indication.

If you're after non-hardening fixer I would try dissolving some of the mystery powder and try it on a scrap of film, check for clearing time.

 

[mshchem]

If you're using the original F-24 formula it would definitely be for the pentahydrate. This is how all the photo formulas were done back in the day. Hypo was the common name for the pentahydrate, that's how Kodak supplied. What you have isn't anhydrous anymore, clearly has absorbed some moisture.

 

[mshchem]

YOU'LL KNOW YOU NEED AN EXHAUST FAN WHEN YOUR PEARL NECKLACE STARTS TO FIZZ!

 

[Jburns]

If you're using the original F-24 formula it would definitely be for the pentahydrate. This is how all the photo formulas were done back in the day. Hypo was the common name for the pentahydrate, that's how Kodak supplied. What you have isn't anhydrous anymore, clearly has absorbed some moisture.

Hi,
Thanks for quick reply. Yes, your last is useful. I’ve been using this 25lb container for 42 years with a 20 year break. Even when it was fresh, I used the 240gms per liter formula and the results are still good from then so I guess it’s wise to continue at 240gms per liter.

 

[mshchem]

Hi,
Thanks for quick reply. Yes, your last is useful. I’ve been using this 25lb container for 42 years with a 20 year break. Even when it was fresh, I used the 240gms per liter formula and the results are still good from then so I guess it’s wise to continue at 240gms per liter.

Perfect, sounds like you are doing it right!!!

 

[Jburns]

If you're using the original F-24 formula it would definitely be for the pentahydrate. This is how all the photo formulas were done back in the day. Hypo was the common name for the pentahydrate, that's how Kodak supplied. What you have isn't anhydrous anymore, clearly has absorbed some moisture.

Thank you for replying and for your insights!

 

[darkroommike]

If you're using the original F-24 formula it would definitely be for the pentahydrate. This is how all the photo formulas were done back in the day. Hypo was the common name for the pentahydrate, that's how Kodak supplied. What you have isn't anhydrous anymore, clearly has absorbed some moisture.

I have a drum of the Kodak stuff (scared to go look at it, imagining one big block) but the stuff was "grain of rice crystals" aka pentahydrate. OK, I looked. It's in a drum, no liner, 30+ years old and mostly still good. I would need to sift it to get rid of the "styrofoam" on top. So I have 50+ pounds of plain fixer.

 

[mshchem]

I have a drum of the Kodak stuff (scared to go look at it, imagining one big block) but the stuff was "grain of rice crystals" aka pentahydrate. OK, I looked. It's in a drum, no liner, 30+ years old and mostly still good. I would need to sift it to get rid of the "styrofoam" on top. So I have 50+ pounds of plain fixer.

That's beautiful! You'll go along way to find stuff that free of impurities. The weird stuff could be dissolved in water and re-crystallized you'd get the nice pentahydrate crystals. (Or even goofier dissolve and adjust specific gravity )

Now that you have 50 pounds of Hypo you need to get busy

 

[Jburns]

That's beautiful! You'll go along way to find stuff that free of impurities. The weird stuff could be dissolved in water and re-crystallized you'd get the nice pentahydrate crystals. (Or even goofier dissolve and adjust specific gravity )

Now that you have 50 pounds of Hypo you need to get busy

I’ll bite . What’s the specific gravity (SPG) of dissolved sodium thiosulfate and, in what proportions of water to sodium thiosulfate to achieve that SPG? I already use hydrometers to test the SPG of the three graded ethanol baths (50/50, 75/25, 90/10) use to dry my processed glass plate silver halide gelatin exposures. I never thought of testing the SPG of my F-24 fix.

 

[mshchem]

I’ll bite . What’s the specific gravity (SPG) of dissolved sodium thiosulfate and, in what proportions of water to sodium thiosulfate to achieve that SPG? I already use hydrometers to test the SPG of the three graded ethanol baths (50/50, 75/25, 90/10) use to dry my processed glass plate silver halide gelatin exposures. I never thought of testing the SPG of my F-24 fix.

Well heck I don't know off the top of my head but I have old Kodak books that would tell me. You'd need to test straight sodium thiosulfate, not a blend of multiple components. Let me check and get back to you.

 

[john_s]

Well heck I don't know off the top of my head but I have old Kodak books that would tell me. You'd need to test straight sodium thiosulfate, not a blend of multiple components. Let me check and get back to you.

You could get close by reading from MDSD docs the density of fixer products (assuming you could find them for sodium thiosulphate fixers these days), since it's mostly thiosulphate, the other ingredients there in minimal amounts.

Alternatively, there are handy solution densities at

Densities of Aqueous Solutions of Inorganic Sodium Salts

Changes in density of aqueous solutions with changes in concentration at 20°C. Density of inorganic sodium salts in water is plotted as function of wt%, mol/kg water and mol/l solution.

www.engineeringtoolbox.com

and then you'd have to do some maths.