Simple way to measure the purity of silver?

[Eli]

It seems to me, from my now distant chemistry classes,  that it should be fairly simple to determine that a one ounce coin is .999 silver.

Seems one could figure out (I haven't yet) how much water one once (or any other quantity) of silver should displace.  This would make picking out good coins from fakes as simple as wieghing a coin and then dropping it in a measuring cup of water.

Am I missing something or is it really that simple?

I submit this idea to the general wisdom for criticism.


PS I was a C chemistry student.

[malcolm]

That is an old issue with silver as money.  All elements heavier than gold are also more expensive than gold, so this test works for gold purity (from a monetary, if not chemical standpoint).

The same cannot be said of silver, however.  An alloy of (let's say) tungsten and zinc might have the same density and visual appearance of silver, but not be silver.

[dalebert]

Silver has a familiar ring to it when it clinks against other silver. That alone prolly makes it far less of a counterfeit threat than FRNs. People hardly glance at those when they take them, at least in units of about $20 or less.

[JonM]

Silver in .999 form should have a fairly specific electrical resistence that an alloyed metal may not be able to match.  I suspect if you could build an affordable device that could actually do this well without damaging the coin you'd be rich

[John Edward Mercier]

Silver has a familiar ring to it when it clinks against other silver. That alone prolly makes it far less of a counterfeit threat than FRNs. People hardly glance at those when they take them, at least in units of about $20 or less.

Anything considered of value will sooner or later be counterfeited.

[ancapagency]

Silver in .999 form should have a fairly specific electrical resistence that an alloyed metal may not be able to match.  I suspect if you could build an affordable device that could actually do this well without damaging the coin you'd be rich

The problem w/ electrical resistance tests is that electrons only travel on the outside--thus a plated coin would test identical to a solid pure coin.

[BaRbArIaN]

There is no *simple* way to gauge purity.  The complex ways vary from x-ray fluorescence, chemical reactions and spectrographic analysis.   If you can heat it up in a flame or shine a very white light on it (even intensity distribution along the whole visual spectrum), you might be able to identify the associated metals it contained (silver has an absorption line at 328.1 nm, copper and aluminum have their own lines which you could verify).

For actual numbers for purity you might have to use the x-ray method (certain peaks have different magnitudes dependent on the number of atoms present).

[dalebert]

Anything considered of value will sooner or later be counterfeited.

Just saying it's harder to counterfeit than FRNs and that people don't worry much about that. I don't think it makes much sense to do complex testing unless you're talking about a large exchange. It's just a matter of doing a little risk/benefit analysis.

[John Edward Mercier]

The paper dollars are continually optically scanned at the banks.
Counterfeits hurt the solvency of a system by making it suspect.

And wouldn't the holdings in precious metals of the masses need to increase significantly for the system to replace the current one?

[BaRbArIaN]

If you at least want to verify that a coin is made mostly of some metal, you could just plug in the diameter and thickness to get a volume and weigh it on a digital scale.  If its density is what you are looking for within a couple percent or so you might be reasonably certain of its purity unless someone does something complicated like coat tungsten slugs with lead and a fine gold layer to balance out to weigh the right amount.  Not worth the trouble for the most part, since once the deception is known, the deceiver's reputation would fall harder than the legitimacy of the Federal Reserve.    That's why I like the x-ray burst method, you get metal peaks and can identify elements in the target.   Might be hard to make one handheld and cheap tho.

[Eli]

I was thinking less handheld and more vendor countertop.

[J’raxis 270145]

Historically, it was more common for people to "cheat" with silver currency, not by counterfeiting it, but by shaving minute amounts of silver off the coin, usually along the edges. Do it to enough coins and you have enough silver to melt down and make a new coin. It's probably more important to guard against this than outright counterfeits.

[Eli]

really accurate scales are a good deal cheaper than they were historically.

[sandm000]

Didn't Ron Helwig post some sort of balance where it only tips if it's a gold coin? You run it through a slot, confirming its volume, then put it on the scale confirming its weight.  Weight/volume = density and this method would be hard to fake.

And as J'raxis has said shaving is more of a problem with silver, if you had these scales for silver you wouldn't need to worry about that, only the shaver would ever have his money rejected.  Although I could see a coin wearing down enough to lose some weight and be rejected, and the niche purchaser would be the Jeweler, you have a piece of silver no one else will take, he'll probably take it off your hands at 90% of face value, or something like that.

Also with modern technology, lasers could measure the object and you could weigh it and you could know instantly (or nearly so) what it was.

[Eli]

Of course this could hardly be worse than inflation.

That is what I've come to realize.  I didn't like the lib dollar at first because it was being called dollars but weren't worth the dollar amount impressed upon them.  But the were worth more than those paper dollars (at least intrinsically).

If enough people will accept coins at the MSRP then they would be better than FRNs in every way.