3 ms·

How were these working copies made? The article makes it seem like there's some "copy" operation you can apply to the reference artifact, but that seems absurd

How were these working copies made? The article makes it seem like there's some "copy" operation you can apply to the reference artifact, but that seems absurd... I Googled "working standard kilogram" (no quotes), in case I'd find some article, and I did find only this: https://www.technology.matthey.com/article/17/2/66-68/ https://www.technology.matthey.com/article/17/2/66-68/ I don't really get a sense after reading, of how these things are used to make more of them.

bo0tzz 8y ago
I would assume you just make an object that will be the working copy, and align it's weight with that of the standard.
- logicallee 8y ago
  How do they align its weight?
  - phs2501 8y ago
    Same way as you machine anything. Start with more material than you need and remove until it is the correct dimensions. In this case, start slightly heavier and polish until it is the correct weight.
    - deleted 8y ago
      [deleted]
  - VLM 8y ago
    The first google term you don't have is "traceable mass calibration NIST" that will lead you to the NIST price list and terms and conditions. They do "double substitution procedure" (another google term) for most masses for about three grand plus or minus incidentials (cleaning, shipping). Unfortunately the best descriptions I can find of NIST double substitution procedure is docx unfree format. However it boils down to a really high quality double arm balance (like a lever with a pivot in middle and buckets on each end) and its temp controlled to keep the lengths of the arms identical and they stick your (test) mass on one side, stack calibration weights on the other side and record what balances, then remove your mass and stack more calibration masses in its place optimistically very similar in mass to the other side, but it won't be equal because one arm is probably a nanometer longer than the other arm or something. Essentially they're testing it twice in order to factor out a difference in arm lengths however small. You can get around eight or nine sig figs of accuracy now a days using this procedure. I would enjoy seeing an electrostatic force balance like they use for microgram scale masses.
    - logicallee 8y ago
      It's hard to imagine that a physical lever-based mechanical scale is so accurate, never would have imagined. Thanks for the detailed comment.
Iwan-Zotow 8y ago
One of the proposals is to replace mole (or define Avogadro constant) and/or kilogram with pure Silicon-28 sphere. So Germans are making sphere (and are leading the project), but Russians are supplying pure Si-28 poly-crystals. Russians deploy centrifuges for nuclear enrichment, but use them to get highly enriched Si-28. Then Germans melt Si-28 and start growing single giant Si-28 crystal. Then it is made into sphere. Then Italians check it for impurity using gammas, neutrons etc. Pretty fascinating Links: https://www.ptb.de/cms/en/research-development/research-on-the-new-si/ptb-experiment/the-kilogram-and-the-mole-counting-atoms/news-for-mass.html?tx_news_pi1%5Bnews%5D=256&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bday%5D=26&tx_news_pi1%5Bmonth%5D=3&tx_news_pi1%5Byear%5D=2015&cHash=8f11b3fc7ca0ef2831957255a771f89a https://www.ptb.de/cms/en/research-development/research-on-t... https://www.ptb.de/cms/en/gateways/press/press-releases/press-release.html?tx_news_pi1%5Bnews%5D=111&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bday%5D=27&tx_news_pi1%5Bmonth%5D=1&tx_news_pi1%5Byear%5D=2011&cHash=fd9981c0438a139ebb2cc7c88b087571 https://www.ptb.de/cms/en/gateways/press/press-releases/pres... https://www.ptb.de/cms/en/research-development/research-on-the-new-si/ptb-experiment/the-kilogram-and-the-mole-counting-atoms/news-for-mass.html?tx_news_pi1%5Bnews%5D=368&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bday%5D=7&tx_news_pi1%5Bmonth%5D=4&tx_news_pi1%5Byear%5D=2015&cHash=7c348b8ffe447becc4db221df9d5f6bf https://www.ptb.de/cms/en/research-development/research-on-t... https://www.chemistryworld.com/news/purest-silicon-sphere-ever-created-will-redefine-the-kilogram/3007588.article https://www.chemistryworld.com/news/purest-silicon-sphere-ev...

bo0tzz 8y ago

I would assume you just make an object that will be the working copy, and align it's weight with that of the standard.

logicallee 8y ago
How do they align its weight?
- phs2501 8y ago
  Same way as you machine anything. Start with more material than you need and remove until it is the correct dimensions. In this case, start slightly heavier and polish until it is the correct weight.
  - deleted 8y ago
    [deleted]
- VLM 8y ago
  The first google term you don't have is "traceable mass calibration NIST" that will lead you to the NIST price list and terms and conditions. They do "double substitution procedure" (another google term) for most masses for about three grand plus or minus incidentials (cleaning, shipping). Unfortunately the best descriptions I can find of NIST double substitution procedure is docx unfree format. However it boils down to a really high quality double arm balance (like a lever with a pivot in middle and buckets on each end) and its temp controlled to keep the lengths of the arms identical and they stick your (test) mass on one side, stack calibration weights on the other side and record what balances, then remove your mass and stack more calibration masses in its place optimistically very similar in mass to the other side, but it won't be equal because one arm is probably a nanometer longer than the other arm or something. Essentially they're testing it twice in order to factor out a difference in arm lengths however small. You can get around eight or nine sig figs of accuracy now a days using this procedure. I would enjoy seeing an electrostatic force balance like they use for microgram scale masses.
  - logicallee 8y ago
    It's hard to imagine that a physical lever-based mechanical scale is so accurate, never would have imagined. Thanks for the detailed comment.

Iwan-Zotow 8y ago

One of the proposals is to replace mole (or define Avogadro constant) and/or kilogram with pure Silicon-28 sphere. So Germans are making sphere (and are leading the project), but Russians are supplying pure Si-28 poly-crystals. Russians deploy centrifuges for nuclear enrichment, but use them to get highly enriched Si-28. Then Germans melt Si-28 and start growing single giant Si-28 crystal. Then it is made into sphere. Then Italians check it for impurity using gammas, neutrons etc. Pretty fascinating Links: https://www.ptb.de/cms/en/research-development/research-on-the-new-si/ptb-experiment/the-kilogram-and-the-mole-counting-atoms/news-for-mass.html?tx_news_pi1%5Bnews%5D=256&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bday%5D=26&tx_news_pi1%5Bmonth%5D=3&tx_news_pi1%5Byear%5D=2015&cHash=8f11b3fc7ca0ef2831957255a771f89a https://www.ptb.de/cms/en/research-development/research-on-t... https://www.ptb.de/cms/en/gateways/press/press-releases/press-release.html?tx_news_pi1%5Bnews%5D=111&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bday%5D=27&tx_news_pi1%5Bmonth%5D=1&tx_news_pi1%5Byear%5D=2011&cHash=fd9981c0438a139ebb2cc7c88b087571 https://www.ptb.de/cms/en/gateways/press/press-releases/pres... https://www.ptb.de/cms/en/research-development/research-on-the-new-si/ptb-experiment/the-kilogram-and-the-mole-counting-atoms/news-for-mass.html?tx_news_pi1%5Bnews%5D=368&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bday%5D=7&tx_news_pi1%5Bmonth%5D=4&tx_news_pi1%5Byear%5D=2015&cHash=7c348b8ffe447becc4db221df9d5f6bf https://www.ptb.de/cms/en/research-development/research-on-t... https://www.chemistryworld.com/news/purest-silicon-sphere-ever-created-will-redefine-the-kilogram/3007588.article https://www.chemistryworld.com/news/purest-silicon-sphere-ev...