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Standard Kilogram Gains Weight
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."'"
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.
If you'd all use imperial, this wouldn't happen. Just need to know how long that guy's foot is.
"First they came for the slanderers and i said nothing."
French do not eat bacon and cheese croissant...
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.
seal it in something already, its not a desk toy. There would be no gunk if it was not exposed to it
It's kind of useless as a reference if no one can actually refer to it.
The mass of X number of molecules of element Y = 1 gram.
Like there is for the second:
"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.
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.
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...
No, it's defined as "the mass of the international kilogram prototype". There are alternative proposals (the Avogadro Project, counting the Silicon-28-atoms in a defined sphere of Silicon-28 and the Watt balance), but none of them is ready yet to replace the Kilogram prototype.
That was the original definition, but it's not precise enough. It's extremely difficult to get water with an exact isotopic composition. VSMOW is used, but even that is not reliably reproducible to the necessary level of precision.
http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water
Also, the density of water is very much related to the temperature and air pressure. Pressure is measured as a unit of force per unit area. Typically, Newtons per squre metre (the Pascal unit). Force, is then in turn defined as a unit of mass times acceleration, with the Newton being 1 kg * 1 ms-2, which obviously results in a cyclically dependent definition, because it would be defined as 1 kg of pure water at a specific temperature and pressure measured in:
Pa = N/m^2 = kg/m*s^2
To get around this problem, you would need to define the Newton in terms of its relationship to other units, ultimately ending up linked to a fundamental constant of nature. The Watt balance approach is trying to do this, by linking the definition with the Ampere. That would reverse the relationship of the Ampere, which is currently defined in relation to the kilogram.
That would then gives a direct way to link those units with the kilogram, and there is no need to precisely measure 1 cubic decimetre of water. You just develop an extremely precise scale that can measure any test mass very precisely and accurately based on the new definition. The difficulty is actually putting that into practice and eliminating as much measurement error as possible. NIST and other laboratories around the world are trying. The problem is, the margin of error in the measurements are still higher than desired.
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