How to determine purity of silver 3N, 3N5?, 4N?

[Iggy-poo]

So what you suggests is to basically use a modified voltammetry system.
https://en.wikipedia.org/wiki/Voltammetry

Göran

Voltammetry looks at current versus voltage. It's all part of the same beast.

 

[snoman701]

TONS...but I want to coin.

So send me sterling, Ill send you crystal.
Thats what I do for another guy who makes his own bars with it.

Clean crystal isn't the hard part. It's making it all the way to sheet without contamination. Simply melting crystals and pouring by no means guarantees you still have fine silver. It should, but you have to be able to prove it to yourself.

If I continue moving in the direction I'm moving right now, I'll be able to go from scrap to clean sheet / coined rounds.

None of this is cheap to set up on the scale I want...which is still not the scale it likely needs to be to actually be profitable.

 

[nickvc]

You can send a sample to the Assay Lab I use in the U.K. They are cheap and quick, it will cost you about $15, if you need assurance.
Guardian Laboratories.
+44121 3598233 speak to Austin.
I believe K.A.Driver used them for the same reason.

 

[Iggy-poo]

You can send a sample to the Assay Lab I use in the U.K. They are cheap and quick, it will cost you about $15, if you need assurance.
Guardian Laboratories.
+44121 3598233 speak to Austin.
I believe K.A.Driver used them for the same reason.

This is the best solution for most people. Just purchasing the standards and references to calibrate the system can be cost prohibitive. I still have some primary standard Silver and a Weston Cell voltage reference from my attempts long ago. It was an interesting project nonetheless.

 

[upcyclist]

You can send a sample to the Assay Lab I use in the U.K. They are cheap and quick, it will cost you about $15, if you need assurance.

I'm gonna have to agree with this one. I'm guessing it wouldn't be too hard to spend $15,000 on training and equipment for a fire assay lab. Some on this forum could set up the lab for less, but they already have the training and experience. Or you could pay someone else [reputable] to assay a thousand different samples at $15 a pop. Or at least a few hundred after postage across the pond

 

[Topher_osAUrus]

The theory behind the Silver Voltameter may be found here and related publications. The Silver Cell was used by the National Bureau of Standards to determine the value of the Ampere, thus the amount of Silver deposited with a known Current over time may be used to calculate the purity of the Silver. With an accurate current meter and scales, it is currently a simple process.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1091173/pdf/pnas01946-0074.pdf

Are you sure? I can't see any way to get purity based on that cell. It is a clever way to relate ampere to mass and my guess is that they are using quite pure silver nitrate in the cell to get a reproducible standard.

Can you make a list of the steps needed to measure fineness?

Göran

Here's a good starting point. The references provided should give you all the information you need. Additional references are available with a simple search at NIST.gov:
http://nvlpubs.nist.gov/nistpubs/jres/84/jresv84n2p157_A1b.pdf

Sorry if this is a stupid question, but, how does this compare to the Silver Coulometer? Or is it wildly unrelated?

 

[Iggy-poo]

The theory behind the Silver Voltameter may be found here and related publications. The Silver Cell was used by the National Bureau of Standards to determine the value of the Ampere, thus the amount of Silver deposited with a known Current over time may be used to calculate the purity of the Silver. With an accurate current meter and scales, it is currently a simple process.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1091173/pdf/pnas01946-0074.pdf

Are you sure? I can't see any way to get purity based on that cell. It is a clever way to relate ampere to mass and my guess is that they are using quite pure silver nitrate in the cell to get a reproducible standard.

Can you make a list of the steps needed to measure fineness?

Göran

Here's a good starting point. The references provided should give you all the information you need. Additional references are available with a simple search at NIST.gov:
http://nvlpubs.nist.gov/nistpubs/jres/84/jresv84n2p157_A1b.pdf

Sorry if this is a stupid question, but, how does this compare to the Silver Coulometer? Or is it wildly unrelated?

Like the blind men trying to describe an Elephant, you are correct in your answer, just a variation of the same. Good answer, by the way.

 

[Topher_osAUrus]

Like the blind men trying to describe an Elephant, you are correct in your answer, just a variation of the same. Good answer, by the way.

Okay, I do believe I am starting to understand the how its possible side of it. (As far as using it to determine purity)
The silver coulometer used a pure silver anode, in a pourus cup, and a platinum cathode with a 10% silver nitrate solution.

The cup, was of course to capture any impurities, and because of faradays laws and what not, the amount of silver deposited over a certain amount of time would always be the same.

So, for running this to determine impurities

Say after a certain run time, at a certain amperage, the deposit would be known. The anode could be weighed, as well as the slimes.(which would probably have a little silver oxide mixed in, so would they need to be ran in nitric and then that solution titrated? -while the undissolved slimes, dried, and weighed?).

Also the electrolyte could be titrated, to make sure that there was no soluble impurities displacing extra silver ions.

(Thats assuming, I was understanding the right principles)

 

[Iggy-poo]

Like the blind men trying to describe an Elephant, you are correct in your answer, just a variation of the same. Good answer, by the way.

Okay, I do believe I am starting to understand the how its possible side of it. (As far as using it to determine purity)
The silver coulometer used a pure silver anode, in a pourus cup, and a platinum cathode with a 10% silver nitrate solution.

The cup, was of course to capture any impurities, and because of faradays laws and what not, the amount of silver deposited over a certain amount of time would always be the same.

So, for running this to determine impurities

Say after a certain run time, at a certain amperage, the deposit would be known. The anode could be weighed, as well as the slimes.(which would probably have a little silver oxide mixed in, so would they need to be ran in nitric and then that solution titrated? -while the undissolved slimes, dried, and weighed?).

Also the electrolyte could be titrated, to make sure that there was no soluble impurities displacing extra silver ions.

(Thats assuming, I was understanding the right principles)

I think it's a bit simpler than that. You have to know the current, time and starting weight, dissolve the sample in Nitric, evaporate to dryness, dissolve in pure water and determine the time it takes to plate the Silver on to the cathode. calculate the Silver plated and divide by the starting weight. You don't have to weigh the cathode, just measure the voltage across the cell and stop counting when the voltage rises at the end point. That will give you the time. You are checking supposed pure Silver, to check the purity. If you try with dirty Silver, you will probably get errors. Keep the max voltage across the cell to 1.34 Volts to keep from plating impurities.

 

[Topher_osAUrus]

If there were traces of copper in said "pure silver", though, would it not have skewed results?
Say 1% Cu contamination.

It dissolves in nitric, would crystalize out during evaporation, dissolve again in pure water, and also plate out during the end of the run when voltage begins to peak from the rise in resistance.(due to lack of conductivity as silver ions are plated out).

It would be a pretty easy contamination to spot though, due to the coloring of the nitric after dissolve. But still, Im not sure if it would play nice using this as a "litmus" test for purity of silver.