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Science

Standard Kilogram Gains Weight 177

Posted by Soulskill
from the too-many-gram-crackers dept.
mrbluze writes "The standard kilogram weights used by countries around the world for calibration have variably increased in mass by tens of micrograms. This poses a threat to the precision and comparability of measurements in science, engineering and trade. The problem is due to surface contamination, but a safe method of cleaning the weights has only recently been devised by the use of ozone and ultraviolet light (abstract). 'The ultraviolet light-ozone treatment removes hydrocarbon contamination that has built up on the metal surface, gunk that comes from the emissions of an industrial society. Cumpson suspects that because the kilos living in national labs have been retrieved and handled more frequently than the international kilo, more carbon-containing contaminants have built up on them over time. Incubating the kilograms with a set amount of ozone and ultraviolet light "gently breaks up the carbonaceous contamination at the surface."'"
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Standard Kilogram Gains Weight

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  • Excellent (Score:5, Funny)

    by mister2au (1707664) on Wednesday January 09, 2013 @01:13AM (#42528745)

    I think the kilogram should be adjusted upwards every holiday season ...

    Nothing like a bit of seasonal normalisation on the scales to justify festive binges.

  • Has anyone measured the standard ounce or hogs head lately?

    BTW: we've spoken with the frenchies, they'll stop feeding the standard KG more than one bacon and cheese croissant per day.
    • by godrik (1287354) on Wednesday January 09, 2013 @01:20AM (#42528787)

      French do not eat bacon and cheese croissant...

  • how do they know this reliably?

    Use the method they used to determine this to define 1KG
    • by Joce640k (829181)

      how do they know this reliably?

      Use the method they used to determine this to define 1KG

      Yep.

      The summary itself says "...the kilos living in national labs have been retrieved and handled more frequently than the international kilo".

      ie. Some of them are stored more carefully than others and aren't gaining as fast.

    • by brelovich (746983)
      The only way to know is to compare the reference weights. The definition of 1kg is that it is the mass of the international 1kg prototype, stored in Paris. It's quite a big problem that it, and the national references, seem to be gaining.
      • The variance was one part in 20 million - well within modern measurement error. Probably about 22-25 million by now as they continued to diverge withing their individual environments.
    • by unixisc (2429386)
      Why not simply define 1 gram as the mass of an Avogadro number of Hydrogen atoms? Solves the issue!
      • Excellent idea. Exactly what is the value of Avogadro's number, again? Unfortunately, it's not quite so simple [wikipedia.org].
        • by unixisc (2429386)
          Okay, 2^79 will be 604,462,909,807,314,587,353,088, which is the nearest exponent of 2 to Avogadro's number. Take this number, divide it by 16 (again, I'm dealing only in powers of 2 here for computational efficiency), and that gives us 37,778,931,862,957,161,709,568. Take that many atoms of C-12, and re-define the kilogram as being the mass of all that. You have a number higher than Avogadros, a total mass less than the weight of C-12 (since I divided by 16), and define that absolute number to be the ma
      • by Goaway (82658)

        Because the definition of a unit has to be implementable as a measurement, so that it can be used to calibrate scales. A purely theoretical definition may be exact, but it is also completely useless if you can't actually build a scale.

        And as we can't count hydrogen atoms, this one doesn't work.

      • Sadly, no. The definition of the kilogram is garbage due to it _imprecision_.

        "It is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Four of the seven base units in the SI system are defined relative to the kilogram so its stability is important."
        http://en.wikipedia.org/wiki/Kilogram [wikipedia.org]

        "In a note to the CIPM in October 2009, Ian Mills, the President of the CIPM Consultative Committee - Units (CCU)

  • Ha! (Score:5, Funny)

    by phantomfive (622387) on Wednesday January 09, 2013 @01:19AM (#42528779) Journal
    If you'd all use imperial, this wouldn't happen. Just need to know how long that guy's foot is.
  • by deek (22697) on Wednesday January 09, 2013 @01:23AM (#42528809) Homepage Journal

    He (or she) redefines the standard.

    Now all we need are electronic scales that can receive updated firmware via the internet.

  • by zippo01 (688802) on Wednesday January 09, 2013 @01:25AM (#42528815)
    That why I'm glad to live in America, where we still use the good old pound. Now all I have to do it sit back and watch your metric world unravel.
    • by boundary (1226600) on Wednesday January 09, 2013 @01:35AM (#42528873)
      I'm glad you're there too.
    • Re: (Score:3, Funny)

      by sidevans (66118)

      The "Pound" is used to weight American Beef, the "Kilogram" is used to measure things like Uranium. Surely you can join the dots from there...

    • two things... (Score:5, Informative)

      by slew (2918) on Wednesday January 09, 2013 @02:10AM (#42529039)

      Although I'm sure you're kidding, it's probably worth bringing up the following 2 bits of trivia

      1. Sadly, the American "pound-weight" has mostly been defined in terms of the kilogram and has its most recent official relationship updated in 1959 (now exactly 0.45359237 kg, down from 0.4535924277 kg back 1901).

      2. The kg artifact itself is soon to be rendered obsolete. In 2014, the kg is likely to be redefined in terms of the planck constant (well technically, planck constant will be fixed to a specific number and since it has the units kg*m^2/s, and the second and meter are defined in terms of oscilations of a Ce133 atom and the speed of light, these will now determine the kilogram).

      That is until we discover a grand unifying theory where the Planck constant is not actually a constant. Then you can really see the world unravel...

      • Re: (Score:3, Informative)

        by Rockoon (1252108)

        2. The kg artifact itself is soon to be rendered obsolete. In 2014, the kg is likely to be redefined in terms of the planck constant (well technically, planck constant will be fixed to a specific number and since it has the units kg*m^2/s, and the second and meter are defined in terms of oscilations of a Ce133 atom and the speed of light, these will now determine the kilogram).

        I suspect that you are a little bit confused. "Planck constant" has no real meaning without agreeing on some units beforehand, and "some specific number" certainly doesnt convey the likely choice.

        The Planck Units [wikipedia.org] are based off the 5 known fundamental physical constants of the universe, where each constant is given the non-arbitrary value of exactly 1.0.

  • by mark-t (151149) <markt@l y n x . b c .ca> on Wednesday January 09, 2013 @01:27AM (#42528823) Journal

    I guess obesity really *IS* an epidemic problem.

    Hey.... somebody had to say it.

    • by Grayhand (2610049)

      I guess obesity really *IS* an epidemic problem.

      Hey.... somebody had to say it.

      The point is the weigh gain isn't just an American problem

  • by lingon (559576) on Wednesday January 09, 2013 @01:36AM (#42528875)

    Just to preempt all comments about imperial or home-grown measurement systems: All measurement systems in the world are defined from the metric base units, which are in turn defined from a few physical constants and this kilogram prototype. When the kilogram prototype gains mass, this affects the kilogram, pound, liter and fluid ounce equally.

    • by hawguy (1600213)

      Just to preempt all comments about imperial or home-grown measurement systems: All measurement systems in the world are defined from the metric base units, which are in turn defined from a few physical constants and this kilogram prototype. When the kilogram prototype gains mass, this affects the kilogram, pound, liter and fluid ounce equally.

      Not for me, I still define the pound as 7000 grains of barley. Must more stable than some unreliable reference standard that let's a little hydrocarbon tarnish screw it up

  • by Joshua Fan (1733100) on Wednesday January 09, 2013 @01:42AM (#42528917) Homepage
    The mass of X number of molecules of element Y = 1 gram.

    Like there is for the second [wikipedia.org]:

    "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."
    • There's supposed to be a redefined kilogram based on the Planck Constant, but that hasn't happened yet. Not until 2014 will they talk about it again. Then maybe they can solve that problem.

    • by denelson83 (841254) on Wednesday January 09, 2013 @01:47AM (#42528945)

      The mass of X number of molecules of element Y = 1 gram.

      Like there is for the second [wikipedia.org]:

      "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."

      Because we don't yet have an accurate-enough measure of the Avogadro or Planck constants.

    • by fufufang (2603203)

      The mass of X number of molecules of element Y = 1 gram.

      Like there is for the second [wikipedia.org]:

      "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."

      Because it is hard to make a standard like that. Counting individual atoms on such a large scale is very complicated.

    • The mass of X number of molecules of element Y = 1 gram.

      First off, it should be atoms not molecules... Secondly, the atomic masses aren't actually constant between atoms. Primarily due to isotopes, but additionally due to electrons (though very minimal they too have mass), so you should also state the charge at least. Ah, but now we know of sub-atomic particles, and may even have discovered and measured the field / particle responsible for mass itself, so we should instead describe mass in terms of interaction with the Higgs Field...

      Ah, but all the quantum

    • Well,there is one proposed.
      This is the Avogadro Project, one of two candidates for a redefinition of the kg, the other
      being the Watt balance.
      You take a lump of isotopically pure crystalline Si (Si 28) and optically polish it to a 'perfect' sphere.
      You then use very accurate laser interferometry to measure the volume of the sphere (and with a suitable set
      of measurements and model you can correct for any residual non-sphericity)
      You use X-ray diffraction to measure the lattice spacing. You can now calculate the

    • Every SI measure will cascade down the 'second' definition:
      - second define meter
      - second & meter define kilogram
      - second, meter & kilogram define Kelvin
      - etc etc

      So we are seriously screwed if we ever decide time is not constant (at least with reference to caesium-133 at rest and 0 K)

      • If that were ever found to be the case, then we could just redefine the second to something that is even more accurate than its current definition to resolve the problem. The new definition would define a new value that is within an acceptably small margin of error (probably on the order of a few femtoseconds or less), such that the new definition doesn't significantly alter the definition of any other units linked with it, at least within any measurable precision.

  • Revised Standard (Score:5, Informative)

    by Thorfinn.au (1140205) on Wednesday January 09, 2013 @02:00AM (#42529003)
    It is being worked upon, to make the kilogram a sphere of a specified diameter of a pure element. The element chosen is silicon and as a mm is defined very well this will avoid all these problems as a new standard can be made and measured repeatably in every country. Did work in this field some years ago with contact with the people involved.
    • by fufufang (2603203)

      It is being worked upon, to make the kilogram a sphere of a specified diameter of a pure element. The element chosen is silicon and as a mm is defined very well this will avoid all these problems as a new standard can be made and measured repeatably in every country. Did work in this field some years ago with contact with the people involved.

      Why didn't they stick with the good old 1 dm^3 of water?

      • water is not an element and a liquid with a high vapour pressure => rapid evaporation
      • What is water? Pure H2O is a myth. You always have H3O+ and OH- in there. Unless they have exactly the same density as H2O then you'll have a slightly varying fault there.
        By the way: water is a universal dissolver. It dissolves literally everything (albeit slowly). So what are you going to make the container out of? As soon as you put the water in there it'll start contaminating the water. Now your dm3 of water is a bit more dense.
        1 dm3 of water is good enough for 99.99% of all cases (guess), but not fo
      • by Goaway (82658)

        "Old" is right. This was the standard from 1791 to 1795. Even in the eighteenth century, people considered this so bad a definition it was only in use for four years.

      • I commented about this elsewhere in the thread, but basically, the density of water is dependent on pressure and temprature. Pressure is dependent on force and area. Force is dependent on mass and acceleration, which creates a cycilical definition. Also, the level of precision and accuracy that water can be measured is not high enough.

  • A few years ago, the kilogram reference standard was losing mass -- coincidentally, they said it had lost 50 g, the amount of mass it's now said to have gained. So it should be just right by now.

    http://www.sciencedaily.com/releases/2007/09/070921110735.htm [sciencedaily.com]

  • by Grayhand (2610049) on Wednesday January 09, 2013 @02:41AM (#42529215)
    It's an archaic system that needs revising. Cleaning something and not expecting it to not change is a little like the heisenberg uncertainty principle. How can you clean something through physical contact and not expect a change?
    • It's an archaic system that needs revising.

      You don't think they don't know this already?

      Of course they know it. It's just very very very hard to come up with a system that can be made independently to represent 1kG with almost no error.

    • by AmiMoJo (196126) *

      We don't have anything better yet. Technology is yet to provide us with a way to measure anything else with more accuracy than a very carefully maintained standard weight.

      • Don't we measure atoms all the time. A kilogram can just be a carbon atom (or some other stable larger molecule) times some large number.
        The only thing that is not going to change mass constantly is an atom

  • Since it is the standard, surely its the world that needs to bend a little (space-time wise) to fit in with the new standard? surely the standard (master) kilo still weighs exactly 1 kg by definition?
  • by gmuslera (3436)
    Maybe the meter is somewhat arbitrary, but in particular weight can be measured against i.e. 1 liter of pure water?
  • http://en.wikipedia.org/wiki/New_SI_definitions [wikipedia.org]

    "The definition of the kilogram is undergoing a fundamental change - the current definition defines the kilogram as being the mass of the international prototype kilogram, the new definition relates it to the equivalent energy of a photon via Planck's constant.

    Current definition: The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

    Proposed definition: The kilogram, kg, is the unit of mass; its magnitude is se

  • Oh, you mean the International scientific community's attempt to redefine the Kilogram? It's called the "dildo" but they are having trouble all agreeing on the proper pronunciation. So for now they're continuing to measure up against this dildo-shaped hunk of alloy that apparently gains weight over the years and every so often has to be rubbed off ceremoniously by a skilled handler with a strap of leather dipped in alcohol.

  • How does this compare to the weight it's been [slashdot.org] losing [slashdot.org] over the years?
  • So a special interest group is pushing for the US to adopt the metric system, and now the kilogram is heavier. This means that American's weighing themselves in metric won't seem as heavy because the number will be lower therefore there will no longer be an obesity crisis in the US.

    To explain it to those still on the imperial system:

    It would be like currently saying you weigh 300 pounds (which is morbidly obese regardless of what the View or Oprah says), but then the standard weight of a pound increases, s

  • They know the volt to a high decimal precession in Josephson junction. There are equations that can convert a volt into a mass.

    Planck's mass has been proposed too. But we dont know the unit of action to enough decimal places.

    The most accurate measurement is the unit of time from atomic excitation in lasers. Thats 14 to 18 decimal places. You have to start taking account of the two kinds of relativities around the 9th decimal place etc. The volt measurement bootstraps off of this.

    Physics Today
  • They should not ever be handled, they should be in a sealed clean room.

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