testing wire for silver and copper

[Lord Refa]

Hi, all, I have an experiment I would like to run. In particular, I have some spools of electrical wire that, when I pulled a piece out to use, I discovered a very shiny surfaces to the strands of wire. To me, it looked like silver or silver-coated copper. I took the exposed strands and put them on a watch glass and added sulfur to see if I would get tarnish, and, yes, the strands turned black in places. I don't believe that tinned wire would have the same reaction, although I may be mistaken, besides which, the strands were too shiny. What I would like to do now is to confirm for silver, and discover if it is solid silver or a silver-coated copper wire, and also, determine the percentage of silver if the silver is just a coating. Any suggestions?

[thompson]

I've never heard of silver-coated copper wire. I'd think that the silver would react with sulfides in the air to form poorly conducting silver sulfide. I think it's more likely that you have tinned copper wire or perhaps even aluminum wire. It it's aluminum, it'll react quickly with HCl.

To do the analysis, simply mass a sample of the wire and put it in a vessel with a measure volume of dilute nitric acid, making sure the acid is in excess. Titrate an aliquot of the solution as described in the book, using potassium chromate as an indicator. If you don't get a precipitate when you start the titration, silver is absent in any measurable amount.

[Lord Refa]

Thanks, Robert, I will give this a go. FYI, silver-coated copper wire is very common, it's used in military equipment as well as audio cables, I have several cables that are marked as such, and will use your information to test the wires that I have picked up at a hamfest.

[thompson]

Thanks, Robert, I will give this a go. FYI, silver-coated copper wire is very common, it's used in military equipment as well as audio cables, I have several cables that are marked as such, and will use your information to test the wires that I have picked up at a hamfest.

I wonder what the purpose is? Given that silver is a better conductor than copper, the only application I could see for silver-coated wire would be in high-voltage applications where surface-effect means the transmission is occuring only at the surface of the wire, so the copper is essentially just serving as a support for the silver conductor.

[Lord Refa]

I am not sure of exactly why, but it is felt that the silver coating provides for better high frequency response due to "skin" effect of electron transport. At any rate, I placed several strands in a test tube, added distilled water followed by nitric acid. It took a while for the reaction to start, but after 2 days the wire completely dissolved as of tonite and formed a greenish solution. I then took a second test tube and added distilled water to that followed by a portion of the dissolved wire solution, then added conc. HCL, this resulted in a colloid of particles in suspension, I'll let it settle, although it may not, being a colloid, and is white in a blue solution.

[Lord Refa]

THe white particles are falling out of solution, very fine and white in color...

[thompson]

Okay, it sounds like silver chloride. You can verify that by adding some dilute (~ 2 M) aqueous ammonia, which should dissolve the precipitate.

[mwechtal]

Thanks, Robert, I will give this a go. FYI, silver-coated copper wire is very common, it's used in military equipment as well as audio cables, I have several cables that are marked as such, and will use your information to test the wires that I have picked up at a hamfest.

I wonder what the purpose is? Given that silver is a better conductor than copper, the only application I could see for silver-coated wire would be in high-voltage applications where surface-effect means the transmission is occuring only at the surface of the wire, so the copper is essentially just serving as a support for the silver conductor.

According to an Electrical Engineer buddy of mine, the purpose in audio cables is to separate people from more of their hard earned money.

Mike

[mevans]

Thats what i have heard about similar things like headphones that have gold plated connector ends