6 ms·

Gold density is 19.30 g/cm3, Tungsten is 19.25. Given two gold bars, one adulterated with Tungsten, and one not, either the weight will differ or the volume wi

Gold density is 19.30 g/cm3, Tungsten is 19.25. Given two gold bars, one adulterated with Tungsten, and one not, either the weight will differ or the volume will differ. So, given equal weights (i.e. standard 400oz bars), you can check the displacement to establish purity. If you use a container that is filled up to a spout, and you measure the displaced water by collecting it in a measuring cup, you can just directly calculate density, and then compare it to gold.

gbhn 12y ago
I don't know anything about this case, but it could be there's a bunch of air trapped inside the bar with the tungsten, assuming the forgers didn't alter the outside dimensions of the bar.
- hippich 12y ago
  bar with tungsten is larger than pure gold bar. so air will not help here.
  - joezydeco 12y ago
    Not if you start with a gold bar, then hollow the core out like a Twinkie and fill it with tungsten and the plug the end. Which I believe is what gbhn was implying.
    - Terr_ 12y ago
      Then the bar is not heavy enough, because you've run out of room to add tungsten on the inside, and adding it on the outside would change the volume or shape of the bar. Tungsten is less dense than gold. Not as much a difference as actual twinkie filling, but either way you're stuck with a similar issue.
yincrash 12y ago
You could match the density with an alloy of a denser metal than gold. Lead - tungsten maybe?
- gatehouse 12y ago
  At least one of the metals in the alloy would need to be higher density than gold. There are a few but I don't think any of them are easy to get: http://www.wolframalpha.com/share/clip?f=d41d8cd98f00b204e9800998ecf8427etuos252jql http://www.wolframalpha.com/share/clip?f=d41d8cd98f00b204e98... EDIT: tungsten + platinum looks viable as sibling comment mentioned.
  - yincrash 12y ago
    Oops! I just assumed lead was denser than gold without checking! I didn't realize how dense gold actually is.
logicallee 12y ago
you can't just check density like that, come on. platinum (which apparently trades around the same price as gold) - has a density of 21.45 [1] which more than compensates. If you want 100 grams of a tungsten-platinum mix to match the weight/volume of 100 grams of gold, this is how many grams you get to use of tungsten: 19.3 * 100 = 19.25 * x + 21.4(100-x) gold is left, mix is right (a sum of the tungsten and platinum parts). I solve for 100 grams because voila, it's now a percentage. That solves to x = 97.7273 (you get to use 97.7273 grams of tungsten) or you just need 2.2727% platinum. (which recall costs about the same as gold.) so if this were a great test people could just use an alloy, which apparently exist: https://www.google.com/search?q=tungsten+platinum+alloy https://www.google.com/search?q=tungsten+platinum+alloy and target the exact same density as gold. tungsten alone seems close enough for them, at least, according to the author. [1] http://en.wikipedia.org/wiki/Platinum http://en.wikipedia.org/wiki/Platinum
- gatehouse 12y ago
  Yeah this looks viable. This would make the best fake bar. I don't think the metal even need to be alloyed, you can just pour in one first, then the other.
  - logicallee 12y ago
    I didn't mean it to be a viable suggestion - I don't think it is one. If you're testing density to within 2.7% you are doing other tests (suggested elsewhere by others in this thread). All I was saying is that although I do think the author is wrong (there is no problem of fake gold bars), the existence of a simple density test isn't why...
    - gatehouse 12y ago
      yeah, this machine seems to be able to do it: http://www.ebay.ca/itm/GoldXpert-SDD-Portable-Countertop-XRF-Analyser-/201085598918 http://www.ebay.ca/itm/GoldXpert-SDD-Portable-Countertop-XRF...
      - 12y ago

gbhn 12y ago

I don't know anything about this case, but it could be there's a bunch of air trapped inside the bar with the tungsten, assuming the forgers didn't alter the outside dimensions of the bar.

hippich 12y ago
bar with tungsten is larger than pure gold bar. so air will not help here.
- joezydeco 12y ago
  Not if you start with a gold bar, then hollow the core out like a Twinkie and fill it with tungsten and the plug the end. Which I believe is what gbhn was implying.
  - Terr_ 12y ago
    Then the bar is not heavy enough, because you've run out of room to add tungsten on the inside, and adding it on the outside would change the volume or shape of the bar. Tungsten is less dense than gold. Not as much a difference as actual twinkie filling, but either way you're stuck with a similar issue.

yincrash 12y ago

You could match the density with an alloy of a denser metal than gold. Lead - tungsten maybe?

gatehouse 12y ago
At least one of the metals in the alloy would need to be higher density than gold. There are a few but I don't think any of them are easy to get: http://www.wolframalpha.com/share/clip?f=d41d8cd98f00b204e9800998ecf8427etuos252jql http://www.wolframalpha.com/share/clip?f=d41d8cd98f00b204e98... EDIT: tungsten + platinum looks viable as sibling comment mentioned.
- yincrash 12y ago
  Oops! I just assumed lead was denser than gold without checking! I didn't realize how dense gold actually is.

logicallee 12y ago

you can't just check density like that, come on. platinum (which apparently trades around the same price as gold) - has a density of 21.45 [1] which more than compensates. If you want 100 grams of a tungsten-platinum mix to match the weight/volume of 100 grams of gold, this is how many grams you get to use of tungsten: 19.3 * 100 = 19.25 * x + 21.4(100-x) gold is left, mix is right (a sum of the tungsten and platinum parts). I solve for 100 grams because voila, it's now a percentage. That solves to x = 97.7273 (you get to use 97.7273 grams of tungsten) or you just need 2.2727% platinum. (which recall costs about the same as gold.) so if this were a great test people could just use an alloy, which apparently exist: https://www.google.com/search?q=tungsten+platinum+alloy https://www.google.com/search?q=tungsten+platinum+alloy and target the exact same density as gold. tungsten alone seems close enough for them, at least, according to the author. [1] http://en.wikipedia.org/wiki/Platinum http://en.wikipedia.org/wiki/Platinum

gatehouse 12y ago
Yeah this looks viable. This would make the best fake bar. I don't think the metal even need to be alloyed, you can just pour in one first, then the other.
- logicallee 12y ago
  I didn't mean it to be a viable suggestion - I don't think it is one. If you're testing density to within 2.7% you are doing other tests (suggested elsewhere by others in this thread). All I was saying is that although I do think the author is wrong (there is no problem of fake gold bars), the existence of a simple density test isn't why...
  - gatehouse 12y ago
    yeah, this machine seems to be able to do it: http://www.ebay.ca/itm/GoldXpert-SDD-Portable-Countertop-XRF-Analyser-/201085598918 http://www.ebay.ca/itm/GoldXpert-SDD-Portable-Countertop-XRF...
    - 12y ago