Several months back my science teacher told me that if you put a zincoln in Hcl or muriatic acid, the copper will be eaten away. so I tried it and this morning i removed the cents. Interestingly enough, the copper was intact but what used to be the zinc was now a pungent smelling black paste.
My way of doing this with students was to file the edge of post 1982 cents to expose the zinc core and then place the coin in a beaker of hydrochloric acid. The next day we could find the thin copper shell floating on the partially spent acid.
I'm afraid your teacher had it backwards, as you found out. Experiments always win. http://chemistry.about.com/od/chartstables/a/Activity-Series-Of-Metals.htm This chart is a general guide; it won't always tell you everything. For example, hydrochloric acid won't normally attack copper, but if the copper is already oxidized, the acid will dissolve the oxide layer. And if there's oxygen dissolved in the water, you can get further oxidation. The end result is that the copper goes away, despite what the table says. Zinc, on the other hand, goes fast when you hit it with almost any kind of acid. Being in contact with the copper actually makes the zinc dissolve even faster! It also protects the copper from further attack while this is happening. It's the same principle as galvanization, except that putting the zinc on the inside is, well, kind of dumb. Nitric acid is both an acid and an oxidizer; it'll dissolve copper pretty quickly. If it's concentrated enough, it'll give off clouds of brown, heavy, and extremely toxic nitrogen dioxide; don't try this at home. (In fact, it's best to avoid nitric acid in general.) It's no use using it to try to "de-plate" the copper off a zincoln; once it gets through to the zinc in one spot, the zinc will go, faster than the copper. It's pretty common knowledge that vinegar (dilute acetic acid) will "restore dates" on Buffalo nickels -- for reasons I don't fully understand, the date and other features don't dissolve as quickly as the fields, and so dissolving a thin layer from the entire coin tends to bring those features out. When I forgot and left a few in vinegar (in a closed container!) for several months, I was surprised to find them copper-colored -- I suppose the vinegar preferentially attacked the nickel from the alloy (see the chart above), leaving the copper behind. Try it with a nickel from your pocket change if you're curious. (Don't do too many, though -- nickel salts, formed when the nickel dissolves, aren't great for the environment.) Can you tell that I think chemistry is fun?
Planchet material for the late '82 and up zents is plated before they are punched. The copper tends to smear over the edge as it is punched allowing minute "bald" spots on the edges. This is where the acid will enter or any thin spot in the plating.
Cents, just like all other coins are punched from coil (sent to the mint from an outside source) in a blanking press. All the mint does is make the coins. They do not perform any plating or refining of metals. They used to start basically from scratch but haven't for many years.
I believe the cent planchets are purchased punched and plated by the mint. Could be wrong but I remember reading that somewhere.
TheCoinGeezer is correct and so are you - mostly. Yes, the planchets are made outside of the mint, but they are individually copper plated and do not have "bald" spots on the edges. The copper plating is complete.
Correct. My understanding is of all production coins cents are the only ones bought as blanks, the rest are punched out of strip at the mint. However, they are looking at cost reduction measures, and one of the biggest could be buying blanks instead of strip. The labor cost at the mint is just entirely too high, so buying prepunched blanks could now save them money. Kind of sad, knowing we have punched our own blanks since the beginning of the mint, but government employees just make way too much salary and benefits versus the private sector.
So, the planchets are punched (out of zinc sheet), then plated with copper, then struck, right? I'd expect that, between striking, normal wear and oxidation, most circulated Zincolns would have at least one flaw in the plating that would let acid through. And once that starts, it tends to accelerate. I feel more experiments coming on. If you're reading this from two hundred years in the future, when most of the zinc cents are gone and the rest are highly collectable, please forgive me.
Stronger acid like pure hydrochloric, sulphuric or nitric acids = completely dissolved metals, plus lots of hydrogen released. Put a balloon over the mouth of the beaker and you will have a lighter than air balloon.
