4 ms·

Kilogram's Future Hangs In The Balance

44 points by vibhavs 17y ago

aerique 17y ago
In one sentence they say the kilogram's been taken out only three times and then later they suggest it might have gotten lighter because of periodic washings. Looking at the picture of how the kg is kept I assume the latter sentence is nonsense. Can someone explain this to me?
- martey 17y ago
  From http://en.wikipedia.org/wiki/Kilogram http://en.wikipedia.org/wiki/Kilogram : Since the IPK and its replicas are stored in air (albeit under two or more nested bell jars), they gain mass through adsorption of atmospheric contamination onto their surfaces. Accordingly, they are cleaned in a process the BIPM developed between 1939 and 1946 known as “the BIPM cleaning method” that comprises lightly rubbing with a chamois soaked in equal parts ether and ethanol, steam cleaning with bi-distilled water, and allowing the prototypes to settle for 7–10 days before verification.
- eru 17y ago
  This may be a better article http://www.nytimes.com/2003/05/27/science/27KILO.html http://www.nytimes.com/2003/05/27/science/27KILO.html. And http://www.bipm.org/en/scientific/mass/pictures_mass/cleaning.html http://www.bipm.org/en/scientific/mass/pictures_mass/cleanin...
abrahamsen 17y ago
What is the problem with defining the kg in terms of the already existing atomic mass unit? See http://en.wikipedia.org/wiki/Atomic_mass_unit http://en.wikipedia.org/wiki/Atomic_mass_unit The atomic mass unit is already associated with the mole, which is in SI.
- tokenadult 17y ago
  There have been attempts to redefine the mole. http://www.iop.org/EJ/article/0026-1394/46/3/022/met9_3_022.pdf?request-id=b198c31a-dd8d-41bc-8f0e-dcc21a0dd920 http://www.iop.org/EJ/article/0026-1394/46/3/022/met9_3_022....
- sethg 17y ago
  I think the trick is to define the kg in terms of something that is not only a universal constant but can also be practically measured. If I redefine the gram as the mass of 6e23 atoms of carbon-12, and you give me a big pile of carbon-12 and say "what's the mass?" and I can't count exactly how many atoms are in the pile, then my definition isn't very useful.
mseebach 17y ago
I thought that a kilogram was the mass of 1000 cubic centimeters of water at melting temperature, and that a centimeter is 1/100 of a meter which is the distance that light travels in a vacuum in the time it takes a caesium-133 atom to emit a little more than 30 periods of radiation (9,192,631,770 p/s / 299,792,458 m/s).
- tokenadult 17y ago
  That was the historical basic idea, but that doesn't provide the kind of precision desired for a very exact definition of the kilogram. The article submitted here reports an attempt at a very precise, ascertainable definition of the kilogram. From the New York Times article kindly linked by eru in another comment: "The kilogram was conceived to be the mass of a liter of water, but accurately measuring a liter of water proved to be very difficult. Instead, an English goldsmith was hired to make a platinum-iridium cylinder that would be used to define the kilogram."
  - mseebach 17y ago
    Yeah, but that's 140 years ago. I'd like to think that we've progress since then. Also, it's pretty important to get the definition right. If my definition is right, then sneezing on the kilogram won't make every weight wrong, if will make the kilogram not quite have the mass of one kilogram.
    - tokenadult 17y ago
      I'd like to think that we've progress since then. The submitted article reports the direction progress has taken since then.
      - mseebach 17y ago
        Yes. I'm merely expressing my surprise that the definition is, in fact, a physical object, and not at this point expressed in terms of other, discreetly measurable quantities.
RyanMcGreal 17y ago
How do the Imperialists do it for the pound (lb)?
- tokenadult 17y ago
  In the United States, customary units are officially defined in terms of metric units.
mildweed 17y ago
Good witty article titling, vibhavs. Its like Fark, but with substance.
- vibhavs 17y ago
  That was actually the original name of the article when I submitted it. Looks like it has now been changed to "This Kilogram Has A Weight-Loss Problem."
sophacles 17y ago
From the article: "... around 50 micrograms (billionths of a kilogram)". Oh NPR -- I thought you were better than that :( Edit: njm below is correct, i misread that as "billionths of a gram)". I rescind my above frowny face and apply it to myself :(
- njm 17y ago
  Am I missing something here? If a microgram is 10^-6 gram and a kilogram is 10^3 grams...
  - sophacles 17y ago
    No, i missed the that they were talking about kilograms not grams. Once again my "no posting on the internet before coffee" rule shows its wisdom... and me my foolishness for ignoring it. Good spot.
Hexstream 17y ago
And I thought the kilogram was defined in some platonic, mathematical way relative to some well-known constant in the laws of physics all along... Also, how did they decide "how much" the initial kilogram should weigh?

44 points by vibhavs 17y ago

In one sentence they say the kilogram's been taken out only three times and then later they suggest it might have gotten lighter because of periodic washings. Looking at the picture of how the kg is kept I assume the latter sentence is nonsense. Can someone explain this to me?

martey 17y ago
From http://en.wikipedia.org/wiki/Kilogram http://en.wikipedia.org/wiki/Kilogram : Since the IPK and its replicas are stored in air (albeit under two or more nested bell jars), they gain mass through adsorption of atmospheric contamination onto their surfaces. Accordingly, they are cleaned in a process the BIPM developed between 1939 and 1946 known as “the BIPM cleaning method” that comprises lightly rubbing with a chamois soaked in equal parts ether and ethanol, steam cleaning with bi-distilled water, and allowing the prototypes to settle for 7–10 days before verification.
eru 17y ago
This may be a better article http://www.nytimes.com/2003/05/27/science/27KILO.html http://www.nytimes.com/2003/05/27/science/27KILO.html. And http://www.bipm.org/en/scientific/mass/pictures_mass/cleaning.html http://www.bipm.org/en/scientific/mass/pictures_mass/cleanin...

abrahamsen 17y ago

What is the problem with defining the kg in terms of the already existing atomic mass unit? See http://en.wikipedia.org/wiki/Atomic_mass_unit http://en.wikipedia.org/wiki/Atomic_mass_unit The atomic mass unit is already associated with the mole, which is in SI.

tokenadult 17y ago
There have been attempts to redefine the mole. http://www.iop.org/EJ/article/0026-1394/46/3/022/met9_3_022.pdf?request-id=b198c31a-dd8d-41bc-8f0e-dcc21a0dd920 http://www.iop.org/EJ/article/0026-1394/46/3/022/met9_3_022....
sethg 17y ago
I think the trick is to define the kg in terms of something that is not only a universal constant but can also be practically measured. If I redefine the gram as the mass of 6e23 atoms of carbon-12, and you give me a big pile of carbon-12 and say "what's the mass?" and I can't count exactly how many atoms are in the pile, then my definition isn't very useful.

mseebach 17y ago

I thought that a kilogram was the mass of 1000 cubic centimeters of water at melting temperature, and that a centimeter is 1/100 of a meter which is the distance that light travels in a vacuum in the time it takes a caesium-133 atom to emit a little more than 30 periods of radiation (9,192,631,770 p/s / 299,792,458 m/s).

tokenadult 17y ago
That was the historical basic idea, but that doesn't provide the kind of precision desired for a very exact definition of the kilogram. The article submitted here reports an attempt at a very precise, ascertainable definition of the kilogram. From the New York Times article kindly linked by eru in another comment: "The kilogram was conceived to be the mass of a liter of water, but accurately measuring a liter of water proved to be very difficult. Instead, an English goldsmith was hired to make a platinum-iridium cylinder that would be used to define the kilogram."
- mseebach 17y ago
  Yeah, but that's 140 years ago. I'd like to think that we've progress since then. Also, it's pretty important to get the definition right. If my definition is right, then sneezing on the kilogram won't make every weight wrong, if will make the kilogram not quite have the mass of one kilogram.
  - tokenadult 17y ago
    I'd like to think that we've progress since then. The submitted article reports the direction progress has taken since then.
    - mseebach 17y ago
      Yes. I'm merely expressing my surprise that the definition is, in fact, a physical object, and not at this point expressed in terms of other, discreetly measurable quantities.

RyanMcGreal 17y ago

How do the Imperialists do it for the pound (lb)?

tokenadult 17y ago
In the United States, customary units are officially defined in terms of metric units.

mildweed 17y ago

Good witty article titling, vibhavs. Its like Fark, but with substance.

vibhavs 17y ago
That was actually the original name of the article when I submitted it. Looks like it has now been changed to "This Kilogram Has A Weight-Loss Problem."

sophacles 17y ago

From the article: "... around 50 micrograms (billionths of a kilogram)". Oh NPR -- I thought you were better than that :( Edit: njm below is correct, i misread that as "billionths of a gram)". I rescind my above frowny face and apply it to myself :(

njm 17y ago
Am I missing something here? If a microgram is 10^-6 gram and a kilogram is 10^3 grams...
- sophacles 17y ago
  No, i missed the that they were talking about kilograms not grams. Once again my "no posting on the internet before coffee" rule shows its wisdom... and me my foolishness for ignoring it. Good spot.

Hexstream 17y ago

And I thought the kilogram was defined in some platonic, mathematical way relative to some well-known constant in the laws of physics all along... Also, how did they decide "how much" the initial kilogram should weigh?