Scratch made fixer gone wrong

[danny_spence]

For years I have always used premade liquid concentrates for

simplicity, and only lately have I experimented with a few simple

chemical formulas in my darkroom. Of particular interest to me are

the so called "odorless" variations. I've been substituting citric

acid for normal stop baths for some time with perfect results. Just

recently I tried making fixer from bulk chemicals. The formula I

used was from Stephen Anchell's The Darkroom Cookbook for "Kodak F-24

Nonhardening Acid Fixer". The formula seems simple enough with only

three dry chemicals -- sodium thiosulfate, sodium sulfide, and sodium

bisulfite. Next to the bisulfite is an asterisk stating that I can

substitute a quantity of citric acid for the sodium bisulfite for

less of a fixer odor. "Fine", I think, and away I go.

 

The formula made one liter of solution. All was well as I carefully

dissolved all of the thiosulfate in hot tap water, then stirred

constantly while I slowly added the sodium sulfide. It certainly

looked like fixer so far. Then I added the citric acid in place of

the bisulfite as described in the book. To my surprise, there was a

brief audible hiss and the solution quickly turned a murky yellow.

The last time I saw fixer look like that, it was when I opened and

prepared a beaten-up forty year old metal army surplus can

labeled "fixer, 10 gallons" with equally ugly results. Wafting the

air from my mixing graduate with my hand, I detected a sharp acid-

like odor. I didn't know what went wrong, however I quickly dumped

the solution down the drain and flushed it with plenty of water. My

plastic mixing graduate has a faint sulfur smell even after several

hot water cleanings (a long HCA soak will probably take care of

that).

 

I studied biology, not chemistry. It would seem the citric acid is

to blame, but can those of you who took chemistry explain why (and

why was it listed as a substitute for sodium bisulfite?) This was

an "acid" fixer, so I'm at a loss as to what went wrong.

[rowland_mowrey]

Go back and look again.

 

Although I am not familiar with the particular formula you reference, I don't think anyone would use Sodium Sulfide in a fixer.

 

Or was this a misprint on your part?

 

Sodium Sulfide in acid can generate the element sulfur along with the poisonous gas Hydrogen Sulfide, which smells like rotten eggs. It is also a very powerful fogging agent for films and papers. Don't let it get loose in your darkroom.

 

Ron Mowrey

[titrisol]

There should be sodium SULFITE in the fixer, not SULFIDE

 

Sulfide is H2-S so it is acid, smells like rotten eggs and it is a gas, leave you beaker in the air for a day or two.

I think the simplest fixer is sodium thiosulfate in water, sulfite and other stuff are additives

 

This is what I used when I made fixer from scratch:

 

Chemical Amount Units

Water (52?C) 500 ml

Sodium thiosulfate (anhy) 150 g

Sodium sulfite (anhy) 10 g

Cold water to make 1000 ml

 

And I guessed you used this one:

WORKING SOLUTION

Chemical Amount Units

Water (125?F/52?C) 500 ml

Sodium thiosulfate (anhy) 152 g*

Sodium sulfite (anhy) 10 g

Sodium metabisulfite 25 g**

Cold water to make 1000 ml

 

*Sodium thiosulfate, pentahydrate (standard prismatic hypo), 240 g, can be substituted for the anhydrous form.

**Substituting 22 grams of citric acid for the bisulfite will eliminate much of the odor associated with fixers.

[danny_spence]

Ron, Paulo - yes, indeed I did mistakenly state sodium sulfide in

my above posting. It should have read sodium sulfite. Lex, if you

see this can you correct my error?

 

The formula - and double checking what I have on hand - is

sodium sulfite. Paulo, the formula I have is essentially identical

to yours. Again, what I used was sodium thiosulfate (anhydrous)

240g, sodium sulfite, 10g, and citric acid, 22g.

[silent1]

Sodium sulfite generates sulfur dioxide on reaction with acids; that's responsible for most of the "fixer odor" with conventional fixers, which are acidified with acetic acid but don't smell much like vinegar (unlike stop baths, which smell like acetic acid and nothing else). Depending on concentrations and quantities, you might have generated enough sulfur dioxide to do what you describe, though that shouldn't happen with a fixer formula from such a well known source (at least not without some of us having heard of it).

 

I wonder if you might have made a similar error when ordering chemicals, to what you did when you typed your original question above -- might you have actually received sodium sufide? Probably not, though; the amount of hydrogen sulfide generated when you added the citric acid would probably have killed you (hydrogen sulfide is more poisonous than hydrogen cyanide, and you lose your ability to smell it, even faintly, at about 1/10 the concentration where it becomes lethal, so the smell is no defense if you hit a heavy concentration).

[rowland_mowrey]

Danny;

 

Ok then, this is probably what took place...

 

The solution was somehow too acid or had too much sodium sulfite in it. When you add acid to sodium sulfite, you get sulfur dioxide, SO2, which is a gas and smells very bad.

 

I really don't know how you got to this point, but that is likely what took place. At the same time, the hypo decomposed due to acidity and formed sulfur and H2S all on its own. This is one route to decomposition of hypo. Release of H2S and sulfur. Bisulfite and sulfite repress it, and acid (too much) hastens decomposition of hypo.

 

Somewhere along the line, one of the chemicals was bad, wrong, or in the wrong amount. Or there was a misprint in the formula.. etc.

 

I can't say at this remove. I can say that the pH range of fix solutions is limited to about 4.5 to 9, maximum range. Sulfite and / or bisulfite should be present to act as an antioxidant. pH adjust should be by using a weak acid or base to prevent shock to delicate hypo molecules and release of toxic gases.

 

Hope you get it right.

 

I use 100 ml /L of 60% ammonium hypo and 10 g/l of sodium sulfite at pH of about 6. If I want a hardener, I use some alum or sodium sulfate in it, or add formaldehyde and go to a pH of 9. I rarely do this though. I use prepackaged. Less hassle.

 

If I can help further, don't hesitate to e-mail me or make another posting, but try to give more information. What you describe is quite unusual. Take it from a guy who mixed up fixers for years. Something went seriously wrong in your lab and you should get to the bottom of it.

 

Ron Mowrey

[lex_jenkins]

Danny, don't worry about the typo. In the context of the thread everything gets straightened out. Leaving the thread intact actually provides additional useful information.

[rowland_mowrey]

Danny;

 

I have tried to respond to your e-mails and your mail server keeps bouncing my messages.

 

It must think I'm SPAM.

 

Sorry.

 

Ron Mowrey

[rowland_mowrey]

To all concerned;

 

The formula referenced by Danny above, from Anchell's book seems to either have a misprint or has left out some information.

 

Through e-mail, Danny and I have been working on the problem and he is close to a solution. Others, please beware that mixing the formula as written, but using citric acid, can generate a large amount of harmful gas and destroy the fix (and maybe even you) completely.

 

Right now, I would avoid the citric acid version of this formula until it is ironed out to Danny's satisfaction.

 

Please be careful out there. Chemicals can be dangerous, and printed formulas can be in error.

 

Regards to all.

 

Ron Mowrey

[danny_spence]

First, thanks to those of you who responded to my question. I've

learned more about the components and functions of

photographic fixer in the past few days than I have on my own in

the many years of practicing photography. I've been working with

Ron Mowrey by means of email on this formula, I have worked

out a solution and largely determined what went wrong.

 

The formula I was following in The Darkroom Cookbook simply

called for Sodium thiosulfate. When I was ordering bulk

chemicals, I ordered the first one I saw, which was Sodium

thiosulfate in anhydrous form. I didn't notice that there were two

forms of the chemical -- anhydrous, and pentahydrate/crystalline.

While not specified, it strongly appears that the formula in The

Darkroom Cookbook calls for the pentahydrate/crystalline form of

Sodium thiosulfate.

 

I believe the formula was thrown off because I used anhydrous

Sodium thiosulfate, when it needed pentahydrate/crystalline

Sodium thiosulfate. I used the same amount of anhydrous for

what should have been pentahydrate. This created a stronger

solution of thiosulfate than what was needed. To compound the

problem, I was only using half of the buffering agent by using

Sodium sulfite alone (following the printed formula exactly) and

leaving the Sodium bisulfite out. The higher than normal

concentration of thiosulfate in the first batch I made with the

inproportionate amount of buffering Sodium sulfite was not able

to cope with the amount of Citric acid called for in the formula.

The Citric acid lowered the PH so drastically that the fixer

decomposed.

 

After first recreating and observing the same results a second

time to ensure my first batch of the formula wasn't a mistake,

With Ron's help I was able to successfully create a batch of the

formula by using less of the anhydrous thiosulfate and citric acid

than called for in the original. I assumed I had all the correct

chemicals for this formula by following the book exactly.

Assumptions are a dangerous thing in chemistry. If anyone

reading this is new to making formulas as I am, do be careful.

[rowland_mowrey]

For all of you interested in Danny's experience with a published formula, you might be interested in this thread:

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=008dQB

 

The gases released during decomposition of Danny's fixer were probably H2S and SO2, Hydrogen Sulfide and Sulfur Dioxide. These are not good for your health.

 

Ron Mowrey

[jordan_w.]

For Anchell and Troop not to specify the pentahydrate or anhydrous form of sodium thiosulfate in this formula is a pretty big error. The molecular weights of these substances are about 248 and 158, respectively, so by using the anhydrous form instead of the pentahydrate you are overshooting the amount of hypo by about 60%. I think I have Anchell's address somewhere from an earlier thread, if you are interested, I can give it to you and you can e-mail him the correction (i.e. to specify which form to use).

 

Generating lots of SO2 in the darkroom is no fun. It and elemental sulfur (your murky yellow observation) are the products of acid degradation of thiosulfate and sulfite, as you and Ron elucidated. I can't see a way to generate H2S from this kind of reaction, though. Getting from sulfite/thiosulfate down to H2S would require a pretty strong reducing agent. I'll check my books if anyone is interested.

 

The organic forms of H2S (thiols or mercaptans) are some of the foulest-smelling stuff on Earth. In grad school there was a guy who worked on the floor below us who was born with no sense of smell. Unfortunately he also occasionally worked with thiols and some of his manipulations led to thiols entering the wastewater stream down sink drains. Thiol vapours would rise through lab sink U-traps and enter every lab in the building -- within minutes he'd have an angry mob of grad students outside his lab door. Tertiary butyl mercaptan is the smelly 'tracer' used for household natural gas IIRC. Doesn't take much to do its job. Ain't chemistry fun?

[rowland_mowrey]

Jordan;

 

I made a guess about the H2S. Some can be generated during decomposition of hypo to sulfur, as are some other noxious things, and my guess was that at that high concentration of ingredients it was possible.

 

If I was wrong, I was wrong, but the SO2 is bad enough.

 

Thanks for the correction.

 

Ron Mowrey