Silver halide in B&W film?

[Leidolf]

Just a simple question : how many grams or in chemistry language hom many MOLS of silver halides is there in a normal B&W film?

 

[Leidolf]

I read in another thread that we have between 300mg of silver halides per square foot and 200mg of silver halides per square foot.
Since a film is roughly 80 square inches vs 144 square inches per square foot, my calculator says roughly 150mg or 0,15 gram of silver halides per film.
That seems little, but is millions upon millions of molecules...

 

[NedL]

That sounds about right... I was going to write that I remember it being 2 or 3 g/m2. That would probably be just the silver, and probably not the bromide or iodide.

Let's see, for silver, there's something like 100g/mole, and a mole is something like 1023 atoms... so there are on the order of 1020 silver atoms on a roll of film. Millions and millions hardly even begins to describe it, even millions OF millions doesn't get very close!!!

 

[Photo Engineer]

It varies widely.

PE

 

[Leidolf]

Yeah i got that from the other thread PE, but in practical terms, ca 0,15 gram on average, and a variation from ca 0.1 gram to ca 0,3 gram per film?
Silver recovery for amatuers suddenly seems a nuisance!

 

[Leidolf]

And..... if only 0,15 gram of silver halides is in every film, there must be a MASSIVE amount of developing agent available in the developer, when Kodak says we only can develop 7 (ideally) to 10 films per litre and we have several grams of developing agent? (I have worked out the molalities but doesn't have them here at the moment, it suggested that the amount of developing agents in D76 suggested 1,5 gram of silver halides per film, so a 10-fold surplus....

 

[Photo Engineer]

That is not entirely true. It can take many moles of developer to effect a small amount of image silver. This exhausts the developer.

Remember, the developer must give consistent results for a rather long time.

PE

 

[Leidolf]

My interest stems from reading up on replenishers. And trying to calculate what we have in solution after adding one litre replenisher (30+ rolls of film) to one litre of D76.

Ideally we should at that point have one litre of D76 - but with a small amount of bromide and iodide ions ions in solution. So I figure the excess of developing agents, in solution and added, balances the halides released.
However the picture is confused by the fact that on average?) only about 25% of the halides in a negative gets developed, the rest ends in the fixer....

 

[Leidolf]

One more question: that one litre of replenished developer, ideally just like a fresh litre of D76, can it be used to develop 7 to 10 additional films WITHOUT any replenisher, or will the heightened halide concentration just stop it catastrophically working?

 

[Leidolf]

That is not entirely true. It can take many moles of developer to effect a small amount of image silver. This exhausts the developer.

Remember, the developer must give consistent results for a rather long time.

PE

OKAY but a 10-fold should take care of that, and obviously have for more than 80 years.

 

[Leidolf]

I'm kinda like uncle scrooge here, if I can develop 33 films with one litre D76 and one litre D76R, and keep time/temperature constant all along, a bonus would be if I could go on to 40 films with what was left after 33 films!

 

[Leidolf]

That is not entirely true. It can take many moles of developer to effect a small amount of image silver. This exhausts the developer.

Remember, the developer must give consistent results for a rather long time.

PE

Quite, quite, also because of the interactivity and synergy between developing agents, metol vs Hydroquinone or Phenidone vs Ascorbate for instance, its hard to calculate how many moles of silverbromide/silveriodide that has been oxidized.

 

[Gerald C Koch]

There are many considerations that control the designg of a replenisher beside replacing used developing agents. Such things a adjusting pH, bromide buildup, ... Things are never simple in photography.

 

[Photo Engineer]

Yes, never simple. Each film differs in the amount of halides released, the ratios, and the absolute quantity of silver. This does not include the per cent developed which varies with each film. I would put the figure to run between 30% and 70% depending on type of grain and halide content.

PE