Anyone good with metals? Here's the problem to solve, suppose

Do some redox chemistry using another reference metal. You should be able to tell if it's oxidizing or reducing based on which metal is plated onto/off of the penny

Clean them all well and measure their resistance. Bronze has a conductivity about twice that of copper and zinc.

>>8554450
Using an induced magnetic field you can make the high conductivity copper coins "jump" further away than the bronze coins. Coin op machines use many ways to check for legit coins, including conductivity.

>>8554450
Pre-1982 pennies are not bronze, they're 95% copper and 5% zinc, which would make them brass if anything.
I separate my pennies by visual inspection and store the old copper ones separately, I've noticed the details on newer copper clad zinc pennies are sharper, but other than that you pretty much have to check the year. Many 1982 pennies are zinc, others are copper. Also color is not a reliable indicator at all, I've seen so many beat to shit blackened pennies that turn out to be from 2002 or something.

The best method would be weight, zinc weighs ~7g/cc, copper weighs ~9. No automatic machines take pennies, so they didn't have to make the weight of the coins the same after the 1982 change.

Weight

>>8554450
Chuck them all into a furnace at about 800F. All the ones that melt are the copper-plated zinc ones.

>>8554450
>What would be the best method for checking the remaining mixture of pennies?

PAY SOMEONE TO FIGURE OUT THE PROBLEM INSTEAD OF TRYING TO GET A FREE ANSWER OUT OF SCI.