Dumb Question About Metal Content

The split is done by weight so you can assume there is a larger volumetric presence of the lower density material.

So in short the OP is right

If coins were gasses we'd all need gas chromatographs to be collectors. An that's a lot bigger investment than a magnifying glass..

I think he got himself as well because he is wrong.



Here he is correct.



Here he is wrong. If there is 50% of each by volume then by definition there can't be more of the lighter one. The less dense one would the same in volume and LESS by weight.



If they are each 50% by volume they would both take up the SAME amount of space.

I'm sure Carl understands what he meant to say, it just didn't come across quite right.

Just two things to note here before we look in detail at your question.

Non-pure coins are rarely weighed in troy ounces so make sure, when you're talking about a .500 fine coin "weighing 1 ounce", that you know which "ounce" you're talking about. To avoid confusion, avoid using the avoirdupois ounce completely: weigh the coin in grams, multiply the weight in grams by the fineness to get the weight of pure silver in grams, then convert that number to troy ounces.

Second, coins that are .500 fine often have other minor constituents other than copper. Most British and all Australian and New Zealand .500 fine coins, for example, are 50% silver, 40% copper, 5% zinc and 5% tin. This composition was chosen because the British discovered that straight 50:50 alloy looked a bit too coppery after it had been in circulation a while.

With regard to the weight/volume question...


To avoid confusion, rather than saying "silver is heavier than copper (per cubic foot)" it would be better to say "silver is denser than copper" or "silver has a higher specific gravity than copper". And the answer, as others have alluded to, is yes, a less dense component of an alloy will take up more space within the alloy's structure for the same amount of mass.

If you take one troy ounce of silver and one troy ounce of copper, melt them both and mix them together, you will get two troy ounces of 50:50 alloy. Mass is not created nor destroyed just by mixing things together - you need a nuclear reaction to do that.

However, one troy ounce of silver has a volume of 2.97 cubic centimetres, while the same mass of copper has a volume of 3.48 cubic centimetres. So an alloy that's 50:50 by weight is actually 46:54 by volume. However, weight percentage is always what is used when measuring content of metals, since the mass is invariable, whereas the volume is not.

It should also be noted that when mixing metals together to make alloys, volume is not always strictly additive - it's a result of the physical properties of the alloy at a macro, micro and molecular level, making it more or less dense than the component metals. But for copper-silver mixtures, the difference is not enough to be statistically significant, so assuming that the volumes are additive is close enough for most real-world work. Our two one-troy-ounce pieces of metal we mixed earlier should have a volume near enough to the "expected" 6.44 cm3.

Thanks, Carl. You're right about that.

Sap -- thank you, that was a wonderfully thorough expostulation on the topic, although since I never took chemistry, I don't know from density. I only know that lead is heavier than aluminum. I'm sorry if my example was too simplistic. I was tyring to keep it simple enough even for me to understand.

The good news is, my suspicions were confirmed, and I thank everybody for their responses.

By the way, although I do know that a troy ounce is different from an avoirdupois ounce, the ounces I'm most familiar with are the fluid kind, and I thin I'll go pour a couple right now.

Happy happy hour, everybody.

Jan