Elizabeth
First off, ALL old wire is corroded.
No.
First, copper doesn't corrode under normal conditions. It's not like steel where any surface corrosion (i.e. rust) continues throughout the metal until it finally turns to dust.
Copper develops an oxide on its surface which acts a protective layer preventing further oxidation.
Second, most of that old WE wire was tin plated copper so it has even further protection against oxidation.
I've had samples of it that was going on 80 years old and it was still in good shape.
Second it is not nearly as pure as ANY current production. (impure means it sucks at transmitting current well)
Insignificant.
Copper used for electrical purposes is only marginally more pure than it was back in 1913 when the International Annealed Copper Standard was set at 5.8 x 10^7 siemens per meter. Conductivity is often referred to as % IACS. Today, the copper used for electrical purposes is only 101% IACS.
As I said, insignificant.
That being said, I WOULDN'T recommend using it for power cords and I'd be careful using it for speaker cables.
If you want to experiment with it, the best stuff in my opinion is the stranded, cotton braid over silk serve which is typically also impregnated with wax.
Check out
Jake's Old Western Electric Stuff store on eBay.
