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WolfTales
08-23-2009, 09:46 AM
I'm not a chemist but I have had 2 years of chemistry in HS and did play around with a chemistry set as a kid.

Will only nitric-ish?-acids-with-silver (silver nitrate) precipitate silver halides? Or can other types of silver acids do that too?

Thanks

Ian Grant
08-23-2009, 09:49 AM
Only nitric acid.

Ian

Photo Engineer
08-23-2009, 10:07 AM
Actually, you could use Silver Acetate or Silver Sulfate among others. The correct term is Silver salt of an acid. All you need is to prepare a soluable Silver + Y salt (Y being any suitable acid that makes a soluable Silver salt). However, historically, Silver Nitrate has been found to be the best.

PE

Ian Grant
08-23-2009, 10:19 AM
That's true but Silver doesn't dissolve in Acetic or Sulphuric acid :D

Usually to form other salts combinations of acids are used, or a silver cyanide is acidified, which is potentially lethal, and not to be tried.

Ian

DannL
08-23-2009, 10:25 AM
About four years ago I was able to produce (what appeared to be) silver chloride using saltwater, coin silver and a 30V DC power source via electrolysis. The result looked like a layer of milk under the saltwater. I removed the excess saltwater and coated ordinary paper with it. Within a few seconds under sunlight it turned a very dark purple. As I recall, the most difficult part of the experiment was getting the correct concentration of salt to water. I made a couple small photograms with keys and leaves, now lost in a book that I can't find. But it was a fun experiment. Were halides produced? Not sure. I'm not a chemist either.

Kirk Keyes
08-23-2009, 10:33 AM
DannL, yes, you made silver chloride.

Ian, he's not asking what acids dissolve silver, but what silver salts can be used to precipitate silver halides.

WolfTales
08-23-2009, 10:36 AM
Cool! So new question now - After one gets a viable silver halide (ie the silver salt precipitates to halide which is photon sensitive):

- Then a photon strikes the halide which bumps an electron up to a higher orbital?

- When developed, the halide gives up an electron and drops back down into a visible silver salt?

That is a neat experiment - thanks for sharing!

Thanks!

Ian Grant
08-23-2009, 10:39 AM
Yes silver can form silver chloride quite easily but then this forms a coating that prevents the process going further.

Ian

WolfTales
08-23-2009, 11:18 AM
Yes silver can form silver chloride quite easily but then this forms a coating that prevents the process going further.

Ian

Well - my question is how the overall chemical mechanism works, not how one variable may stop the process.

Ian Grant
08-23-2009, 11:33 AM
Sorry I was answering DannL's point, but by the time I finished eating my evening meal you & Kirk had posted :D

There's an excellent Kodak film (video) online about how film is made and how the whole process works, someone posted a link to it a few weeks ago. It's well worth watching as it's talked about in laymans terms and explains excatly what you're asking. Sorry I can't remember the link.

Ian

WolfTales
08-23-2009, 11:44 AM
Well, my resources are pretty tight right now regarding time constraints etc... if anybody would actually not mind giving me a brief run down, this is of course aside from Ian Grant, I would be very thankful!

Thanks

dwross
08-23-2009, 11:53 AM
Sorry I was answering DannL's point, but by the time I finished eating my evening meal you & Kirk had posted :D

There's an excellent Kodak film (video) online about how film is made and how the whole process works, someone posted a link to it a few weeks ago. It's well worth watching as it's talked about in laymans terms and explains excatly what you're asking. Sorry I can't remember the link.

Ian

http://www.thelightfarm.com/cgi-bin/showvideo.py

Ian Grant
08-23-2009, 11:54 AM
Just try here. (http://www.apug.org/forums/forum205/59587-subtitled-kodak-1958-film-how-film-made.html)

We were posting at the same time.

I have seen one in English too.

Ian

Photo Engineer
08-23-2009, 12:01 PM
That's true but Silver doesn't dissolve in Acetic or Sulphuric acid :D

Usually to form other salts combinations of acids are used, or a silver cyanide is acidified, which is potentially lethal, and not to be tried.

Ian


And, the reason that Silver Nitrate is used is that the processes to make the Acetate or Sulfate are more complex and more expensive! Thus they are not used.

Silver Cyanide is more of a combination salt and complex, akin to Silver Thiocyanate or Silver Thiosulfate and is not predisposed to precipitate out with halides very well to grow a crystal.

With sea salt, you get a mixture of halides that precipitate with Silver and thus you get a Cl/Br/I mixture proportionate to the solubilities of the halides and their concentrations in your particular portion of seawater. In addition, the presence of Mg, Ca and etc... ions will tend to influence the type of crysal you get. This ambiguity is not considered good for making repeatable crystals but will work.

PE

WolfTales
08-23-2009, 12:06 PM
Thanks so much!

Kind regards everyone!

Photo Engineer
08-23-2009, 12:09 PM
Cool! So new question now - After one gets a viable silver halide (ie the silver salt precipitates to halide which is photon sensitive):

- Then a photon strikes the halide which bumps an electron up to a higher orbital?

- When developed, the halide gives up an electron and drops back down into a visible silver salt?

That is a neat experiment - thanks for sharing!

Thanks!

Basically, when light strikes a Silver Halide crystal, a latent image is formed by at least 3 Silver ions which form a stable Silver center by gaining an electron. Ag+ -> Ag metal (3 atoms worth) and so we use 3 photons minimum.

During development, these 3 Atoms of neutral silver are then centers for rapid catalytic amplificaiton as developer is oxidized and silver is reduced. Halide is released as a negative ion in solution, developer is oxidized and Silver metal is left as a solid deposit. Silver ion therefore gains an electron to become neutral, developer loses an electron to become oxidized, and halide drifts off into the developer solution which is becoming more acidic due to the oxidation of developer.

HQ + Ag+ + OH- -> Qinone + Ag metal + H+
Quinone + Sulfite -> HQMS (hydroquinone monosulfonate ion)

Hope this helps. It is very very simplified though.

Key words to research "Gurney Mott theory of latent image formation"
Mees and James, chapters on latent image formation and development
Haist same as Mees and James but somewhat simpler language IMHO.

PE

DannL
08-23-2009, 12:43 PM
Yes silver can form silver chloride quite easily but then this forms a coating that prevents the process going further.

Ian

If memory serves, the silver chloride flowed off into solution as the salt water at the level of the plates became more and more satuated. An occasional cleaning of the plates does help. There was a distinct layer between the clear salt water above and the silver chloride in solution. I guess silver chloride is heavier than salt water. In this experiment I can't recall if both anode and cathode were silver, or if one plate was stainless steel and the other silver. I had tried just about everything up to the point of success, and then all my brain cells seized up completely with the excitement. They have remained that way ever since. :D

Ian Grant
08-23-2009, 12:55 PM
Coin silver isn't that pure, it usually depends on the age but the content went down in the alloys so it's not the same as converting pure silver. The other metals will be removed far more easily.

Ian

Photo Engineer
08-23-2009, 12:58 PM
Copper in coin silver can interfere badly with imaging.

Crystal formation suitable for imaging does not go well if there is no gelatin. The grains tend to clump or to fog. There are several exact formulas posted here on APUG that might help.

PE

WolfTales
08-23-2009, 01:18 PM
Wow - incredible - so the crystal actually turns into a metal by the sheer proximity of the laticework of neighboring atoms with higher energy orbits - and then that gets amplified by the developer...

So going from a salt to a halide to a metal and then amplified!