Rapid fixer without Ammonium thiosulfate

Hello

Some my research with well known Agfa-304 formula for rapid fixer without Ammonium thiosulfate:

Water at 52°C – 750ml
Sodium Thiosulfate – 200g
Ammonium Chloride – 50g
Potassium Metabisulfite – 10g
Water to make 1 litre

Idea is that Sodium Thiosulfate + Ammonium Chloride --> Ammonium thiosulfate. So we can write reaction:

Na2S2O3·5H2O + 2NH4Cl = (NH4)2S2O3 + 2NaCl + 5H2O

molar mass:

MW(Na2S2O3·5H2O) = 248.18
MW(NH4Cl) = 53.49

100g of Sodium Thiosulfate + 43.1g of Ammonium Chloride --> 59.7g of Ammonium thiosulfate

so in Agfa-304 formula only part of Sodium Thiosulfate convereted to Ammonium thiosulfate:

200g of Sodium Thiosulfate + 50g of Ammonium Chloride --> 84g of Sodium Thiosulfate + 69.26g of Ammonium thiosulfate

for full reaction we need 86g of Ammonium Chloride. and final formula will be:

Water at 52°C – 750ml
Sodium Thiosulfate – 200g
Ammonium Chloride – 86g
Potassium Metabisulfite – 10g
Water to make 1 litre

I don't known why Agfa-304 rapid fixer contains less Ammonium Chloride than required.

Second thing is that Ammonium Chloride can be replaced with Ammonium Sulphate (NH4)2SO4 (in my chem.store A.Sulphate in twice cheap than A.Chloride). Reaction will be next:

Na2S2O3·5H2O + (NH4)2SO4 = (NH4)2S2O3 + Na2SO4 + 5H2O

molar mass:

MW(Na2S2O3·5H2O) = 248.18
MW((NH4)2SO4) = 132.14

100g of Sodium Thiosulfate + 53.24g of Ammonium Sulphate --> 59.7g of Ammonium thiosulfate

rapid fixer formula with Ammonium Sulphate:

Water at 52°C – 750ml
Sodium Thiosulfate – 200g
Ammonium Sulphate – 107g
Potassium Metabisulfite – 10g
Water to make 1 litre

Other known formula with Ammonium Chloride/Sulphate is Kodak F-7/F-9:

Kodak F-7
Water, at 125F (see note below) 600.0 ml
sodium thiosulfate, crystals 360.0 grams
Ammonium Chloride 50.0 grams
Sodium Sulfite, anhydrous 15.0 grams
Acetic Acid, 28% 48.0 ml
Boric Acid, crystals 7.5 grams
Potassium aluminum sulfate 15.0 grams
Water to make 1.0 liter

F-9 is the same except for substituting
Ammonium sulfate 60.0 grams
for the ammonium Chloride above.

in both case as result we have mix of Sodium thiosulfate and Ammonium thiosulfate (~100g) in fixer solution, because amount of Ammonium salt is low!

As we known Agfa-304 fixer is slow than true Ammonium thiosulfate rapid fixer. I found state that NaCl salt decrease speed of fixing. But maybe problem in low amount of ammonium salt?

There were commercial reasons for these fixers, until the widespread use of colour films Ammonium Thiosulphate was far more expensive and so uneconomic, it was only when the volume of production rose that costs dropped very significantly that it became economic and the older formulae were dropped.

These reactions are equilibriums so as Thiosulphate reacts with the Silver halides there's an excess of Ammonium ions.

Ian

I can recall PE making references in the past that at one point Amm Thio was shipped as whole railway tank cars. Volume has dropped off, so that was a way of the past.

commercial reasons is interesting, but not reply to my question - why Agfa-304 use mix Sodium Thiosulfate and Ammonium thiosulfate in approx 1:1 proportion instead of complete reaction?

Relayer said:

commercial reasons is interesting, but not reply to my question - why Agfa-304 use mix Sodium Thiosulfate and Ammonium thiosulfate in approx 1:1 proportion instead of complete reaction?

Click to expand...

It's an old formula, before ammonium thiosulphate was available. It doesn't need to be a complete reaction the Ammonium ions help with the solubility of the silver thiosulphate reaction which in turn releases Ammonium & Chloride ions again which means it doesn'y need to be added as a 1:1 proportion.

Ian

I think the question being really asked here is would it be worthwhile/practical to add enough of the ammonium based chemical to fully react with the Hypo? Whold that even work or do the old formulas represent the most that can be expected to react....

ammonium thiosulphate is normally supplied as a liquid with a relatively short shelf life. a powder that was stable which has the fixing power of a Liquid fixer concentrate might be a useful formala to have on hand. I know I can get the Ilford rapid fixer with a slight delay at a local store. I don't dare mail order liquid fixer in the winter.

An all powder fixer would not have that worry. The cost factor may be overshadowed by the convenience factor.

I also wonder if the Amaunium Thiosufate is also used as a water treatment chemical? which would assure it being available on the market.

ORWOCOLOR 73 - Fixing Solution
1. Sodium thiosulfate, anhydrous .................. 120.0 g
2. Ammonium chloride ................................... 80.0 g
3. Water to make ............................................... 1 L

MW(Sodium thiosulfate, anhydrous) = 158.11, so 120g of Sodium thiosulfate anh required ... 81.2g of Ammonium chloride for full reaction. Bingo!

cmacd123 said:

I think the question being really asked here is would it be worthwhile/practical to add enough of the ammonium based chemical to fully react with the Hypo?

Click to expand...

Sodium thiosulfate, ammonium chloride, and ammonium sulfate are ionized in solution. What is present is sodium, ammonium, thiosulfate, chloride and sulfate ions. There can be no reaction between the ammonium salt and the sodium thiosufate because these compounds do not exist in water solution.

The addition of an ammonium salt to a sodium thiosulfate fixing bath results in an increase in the rate of removal of silver halide from an emulsion. HOWEVER, the rate is slower than a comparable ammonium thiosulfate bath. The "unwanted" sodium, chloride or sulfate ions slows the rate.

Discharge of ammonium salts into water supplies is a problem since the ammonium ions are toxic to fish. There is at least one patent which states that 60 mole percent of the ammonium thiosulfate can be replaced with sodium thiosulfate. However, I could find no discussion as to the efffect on the fixing speed of the resulting mixture.

Kodak suggested the use of ammonium sulfate instead of ammonium chlroide which it is corrosive to some stainless steels. However the ammonium sulfate containing fixer is less effective in its action.

I was make some experiment. Mix 3 solution:

Solution 1 same as Agfa-304 (without metabisulfite )
Sodium Thiosulfate – 200g
Ammonium Chloride – 50g
Water to make 1 litre

Solution 2 with increased amount of Ammonium Chloride
Sodium Thiosulfate – 200g
Ammonium Chloride – 86g
Water to make 1 litre

Solution 3 with Ammonium Sulphate with amount from formula (see my 1st message)
Sodium Thiosulfate – 200g
Ammonium Sulphate – 107g
Water to make 1 litre

Solution 4 with exceed amount of Ammonium Chloride
Sodium Thiosulfate – 200g
Ammonium Chloride – 130g
Water to make 1 litre

clearing time at +18C:
Solution 1 - 85sec
Solution 2 - 35sec
Solution 3 - 43sec
Solution 4 - 64sec

So increasing amount of Ammonium Chloride to correct molar ratio with Sodium Thiosulfate decrease clearing time in ~2.5 times. Increasing amount of Ammonium Chloride more than required will fixing slow.
Can't test "true" Ammonium thiosulfate solution because haven't it ((

Arrived my pH-meter and I can make some measurement.



Clearing time is relative to Agfa-304 clearing time. I claim: increasing amount of Ammonium Chloride from 50 to 85g/l in Agfa-304 make fixer in 2 times faster. This improvement not depended from pH or amount sulfite/metabisulfite. Usage Ammoniom Sulphate instead of Chloride give us more slow fixer (see case 6,7,8). I think that this is due to the fact that Sodium Sulphate working as anti-swelling agent and reduces the diffusion rate in the emulsion.

An old american journal of 1888 had similar results with ammonia water, ammonium actetate and ammonium sulfite. I would think that a combination of ammonium sulfite and sodium thiosulfate would make a good fixer.

BTW, the other reason for using ammonium is that it is much better at dissolving silver iodide.