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Message:: [QUOTE="-jeffB, post: 1101846, member: 27832"]Oh, my. Okay, please point me to a source of 1.000 purity gold. Gold is relatively easy to purify, and we have all the resources of modern metallurgy at our fingertips. Surely someone must be producing it, right? Wrong. Well, almost wrong -- materials scientists do use atomic force microscopy to manipulate single, isolated gold atoms, so you could safely claim that those are 100% pure gold. They've even produced nanoclusters with dozens of gold atoms, and if you work at it, you can produce such clusters with a very low probability of including any other atoms. But gather enough of them together to make a block that you can weigh, measure, and use as a standard? No. Not even today. The purest materials that we can produce in bulk today are the semiconductors used to make integrated circuits. Bulk silicon is the basis for these chips, and today we can routinely purify it to better than .999999 (<1 ppm impurity), with certain contaminants controlled at an even lower level (<a href="http://books.google.com/books?id=n5zMiMfw6ZUC&pg=PA13&lpg=PA13&dq=purest+materials+part+per+trillion&source=bl&ots=cTvWnCKzIH&sig=P8GgBDXJuD_SFQDdkAj9YIDJO8k&hl=en&ei=abFWTY39BIiPtwfqzqz-DA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCcQ6AEwAw#v=onepage&q&f=false" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://books.google.com/books?id=n5zMiMfw6ZUC&pg=PA13&lpg=PA13&dq=purest+materials+part+per+trillion&source=bl&ots=cTvWnCKzIH&sig=P8GgBDXJuD_SFQDdkAj9YIDJO8k&hl=en&ei=abFWTY39BIiPtwfqzqz-DA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCcQ6AEwAw#v=onepage&q&f=false" rel="nofollow">here's a reference</a>). But to get to that level or purity, you need process that are ridiculously complex, finicky, and EXPENSIVE. So, how do you determine that something is .999 pure if you don't have a 1.000 pure sample for comparison? That's actually really easy. There are ways to separate out and measure contaminants -- it's just that you can't do it without introducing other contaminants. So, for example, suppose I've got a gram of silver. I could take one tenth of it (100 mg), do a separation that gets out 99% or so of the copper it contains, and measure that at (say) 10 micrograms. That shows that the sample was 0.0001 (0.01%) copper. You can do similar procedures to measure other common contaminants, add them all up, and you know how much of your sample was not silver -- and, from that, it's easy to tell how much was silver. This is a branch of chemistry called "quantitative analysis", it's very, very old, and it has never relied on the existence of "100% pure" reference standards. Yes, there are economic reasons to debase coinage. But they also "did not want to produce pure metal" because they quickly reached a point where small increases in purity meant huge increases in expense and waste -- and, not far beyond that, where further increases in purity were not possible. At some point, I suppose we're arguing about specific numbers, and I'm short on those. But I know that "100% purity" is off the table, and I know that you don't need a pure standard to determine a sample's purity.[/QUOTE]

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