Standard Kilogram Gains Weight

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Standard Kilogram Gains Weight

Posted by Soulskill on Tuesday January 8, 2013 @06:10PM 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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Excellent by mister2au · 2013-01-08 18:13 · Score: 5, Funny

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.
1. Re:Excellent by Acapulco · 2013-01-08 18:27 · Score: 5, Funny
  
  I came here to ask precisely this.
  So I've actually lost weight? Woohoo! go science!
  
  --
  Slashdot. Unreadable news to annoy nerds. - wonkey_monkey
begs the question... by johnsnails · 2013-01-08 18:19 · Score: 2

how do they know this reliably?

Use the method they used to determine this to define 1KG
1. Re:begs the question... by Joce640k · 2013-01-08 18:48 · Score: 2
  
  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.
  
  --
  No sig today...
2. Re:begs the question... by Kell+Bengal · 2013-01-08 22:50 · Score: 2
  
  Excellent idea. Exactly what is the value of Avogadro's number, again? Unfortunately, it's not quite so simple.
  
  --
  Scientists point out problems, engineers fix them
  altslashdot.org: The future of slashdot.
3. Re:begs the question... by petermgreen · 2013-01-09 02:12 · Score: 4, Informative
  
  Isn't the definition of a gram the mass of 1 cm3 of water?
  No, that was how it was initially defined but in 1799 they moved to using metal prototypes.
  
  Would this not be a standard you could employ in any lab without the need for the international 1Kg prototypes?
  It's trickier than it sounds. Between the difficulty of accurately measuring out the liquid, the fact that density changes with temperature and pressure, the fact that isotopic mixes can vary and the fact that our units of pressure are in themselves based on the kilogram making the definition recursive this becomes a difficult definition to apply accurately.
  There is talk of moving to a definition based on fundamental physical units but it's difficult to get the experimental results consistent and stable enough (IIRC two different methods for determining avagadros number were giving slighly different results).
  
  --
  note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
4. Re:begs the question... by Lachlan+Hunt · 2013-01-09 02:12 · Score: 5, Informative
  
  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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  By reading this signature, you hereby agree with the content of the above comment.
Ha! by phantomfive · 2013-01-08 18:19 · Score: 5, Funny

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."
1. Re:Ha! by phantomfive · 2013-01-09 04:34 · Score: 3, Interesting
  
  Behold!
  
  --
  "First they came for the slanderers and i said nothing."
Re:Mititant metric user by godrik · 2013-01-08 18:20 · Score: 5, Informative

French do not eat bacon and cheese croissant...
How does a geek lose weight? by deek · 2013-01-08 18:23 · Score: 4, Funny

He (or she) redefines the standard.
Now all we need are electronic scales that can receive updated firmware via the internet.
Glad to be an American. by zippo01 · 2013-01-08 18:25 · Score: 5, Funny

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.
1. Re:Glad to be an American. by boundary · 2013-01-08 18:35 · Score: 5, Funny
  
  I'm glad you're there too.
2. Re:Glad to be an American. by sidevans · 2013-01-08 18:45 · Score: 3, Funny
  
  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...
  
  --
  I'm not signing anything
It's happening *everywhere* by mark-t · 2013-01-08 18:27 · Score: 4, Funny

I guess obesity really *IS* an epidemic problem.
Hey.... somebody had to say it.

--
File under 'M' for 'Manic ranting'
Re:whats the problem by BradleyUffner · 2013-01-08 18:28 · Score: 5, Insightful

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.
This affects all measurement units by lingon · 2013-01-08 18:36 · Score: 3, Informative

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.
1. Re:This affects all measurement units by hawguy · 2013-01-08 19:08 · Score: 2
  
  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
Why isn't there a precise atomic standard? by Joshua+Fan · 2013-01-08 18:42 · Score: 2, Insightful

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."
1. Re:Why isn't there a precise atomic standard? by Areyoukiddingme · 2013-01-08 18:46 · Score: 2
  
  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.
2. Re:Why isn't there a precise atomic standard? by denelson83 · 2013-01-08 18:47 · Score: 5, Informative
  
  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.
3. Re:Why isn't there a precise atomic standard? by hyperfine+transition · 2013-01-08 21:16 · Score: 2
  
  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 number of atoms
  in the sphere. There are also corrections for the oxide layer at the surface,residual impurities etc.
  The nice thing, apart from the kg being defined by dimensional measurements (which are then traceable to the SI second) , is that if you chip your kg standard, you just repolish it and remeasure it.
  You then define what one kg is by saying a certain number of Si 28 atoms is equal to 1 kg. This number would be chosen to agree as closely as possible with the current definition of the kg. This process is similar to the way the second was redefined, from an astronomically defined value to a value defined by a microwave transition in the caesium atom.
Comment removed by account_deleted · 2013-01-08 18:54 · Score: 2

Comment removed based on user account deletion
Revised Standard by Thorfinn.au · 2013-01-08 19:00 · Score: 5, Informative

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.
1. Re:Revised Standard by Neil+Boekend · 2013-01-08 19:46 · Score: 2
  
  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 for some sciences.
  
  --
  Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
two things... by slew · 2013-01-08 19:10 · Score: 5, Informative

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...
1. Re:two things... by Rockoon · 2013-01-08 19:52 · Score: 2, Informative
  
  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 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.
  
  --
  "His name was James Damore."
Re:Definition by Dahamma · 2013-01-08 19:14 · Score: 2

As long as you can exactly count all of the atoms in a weight. Otherwise it's more useless for comparative measurement than a king's foot.
Re:It used to be losing mass by hawguy · 2013-01-08 19:25 · Score: 3, Informative

50g! Forget Avogadro's constant and spheres of silicon, I could do better than that with a brick and a shoebox.
Oh sorry, I typed "50 ug", but I used an ASCII "mu" but it seems to have been eaten by Slashdot and I didn't notice it in the preview. For the record, Slashdot doesn't accept the µ HTML entity either)
The truth is by Grayhand · 2013-01-08 19:41 · Score: 2

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?
1. Re:The truth is by serviscope_minor · 2013-01-08 21:06 · Score: 2
  
  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.
  
  --
  SJW n. One who posts facts.
2. Re:The truth is by AmiMoJo · 2013-01-09 00:41 · Score: 2
  
  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.
  
  --
  const int one = 65536; (Silvermoon, Texture.cs)
  SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
Re:Definition by Sique · 2013-01-08 19:51 · Score: 5, Informative

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.

--
.sig: Sique *sigh*
Re:Mititant metric user by jrumney · 2013-01-08 20:08 · Score: 4, Funny

Lard et fromage then, you informative pedant.
Re:It used to be losing mass by Xtifr · 2013-01-08 20:41 · Score: 4, Informative

There is no ASCII mu. ASCII is a seven-bit encoding which only covers unadorned latin alphabetic characters, arabic digits, and some random punctuation. Even latin1 (aka ISO8859-1) lacks a mu character. I'm not sure what you think you typed, but it definitely wasn't ASCII.
There's also the problem of potential confusion between U+00B5 MICRO SIGN and U+03BC GREEK SMALL LETTER MU (among others), but neither of those is remotely ASCII.
Anyway, yeah, slashdot sucks when it comes to international character support.
1kg is 1 kg by dave69 · 2013-01-08 21:08 · Score: 2

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?
Re:whats the problem by sFurbo · 2013-01-08 21:27 · Score: 3, Informative

The kilogram is sealed and only taken out every approximately every 50 years or so to compare to the secondary standards (and being cleaned, I think). It has apparantly lost weight relative to the secondary standards.
you can read all about then new kg by slew · 2013-01-08 21:38 · Score: 2

You can read all about the new kg here...
Re:Mititant metric user by damaki · 2013-01-08 22:06 · Score: 2

I am French and, well, we should. This sounds amazing and definitely mouth-watering.
And BTW, ham, cheese and "bechamel" croissant is really tasty. One could easily replace the ham with crispy bacon.

--
Stupidity is the root of all evil.
Re:You are wrong by slew · 2013-01-08 22:24 · Score: 4, Informative

Perhaps you should read this document from NIST about the history of weights and measures in the US.
According to this document...
1827 a troy pound was obtained from London.
1828 a brass artifact (which was compared to this troy pound) declared standard for the US mint, not the avoirdupois pound
1866 the metric system was made lawful for commerce in the US. Legally defines avoirdupois pound as (1/2.2046) kg
1875 17 governments (incl the US) established the international bureau of weights and measures
1890 The US receives standard kilogram artifacts #4 and #20 for use as the national prototype
1894 The US tweaks the definition of the pound relative to this kilogram artifact to make it closer to the UK pound
The US makes various other tweaks over the years in the pound's definition relative to the standard kilogram artifact that the US government maintains.
The "troy" pound artifact is only used for Mint operation in the US and is not related to the avoirdupois pound used in commerce.
Also all NIST calibrations are done in metric units (as of 1959).
Re:Water? by Goaway · 2013-01-09 02:02 · Score: 2

That is many orders of magnitude less exact than the current standard.
Re:The meter is based on the speed of light by Lachlan+Hunt · 2013-01-09 02:26 · Score: 2

The density of water is dependent on temperature and pressure. Pressure is defined as a unit of force per unit area (Newtons per square metre). Force is subsequently defined in terms of mass times acceleration (1 N = 1 kg * 1 m/s^2). Congratulations, you have just created a definition of mass that is dependent on itself. Also, the ability to purify water and measure its volume to a high enough accuracy and precision is extremely difficult.

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Re:Mititant metric user by kelemvor4 · 2013-01-09 03:31 · Score: 2

French do not eat bacon and cheese croissant...
Only fries and toast, right?
Re:It used to be losing mass by hawguy · 2013-01-09 06:27 · Score: 2

There is no ASCII mu. ASCII is a seven-bit encoding which only covers unadorned latin alphabetic characters, arabic digits, and some random punctuation. Even latin1 (aka ISO8859-1) lacks a mu character. I'm not sure what you think you typed, but it definitely wasn't ASCII.
There's also the problem of potential confusion between U+00B5 MICRO SIGN and U+03BC GREEK SMALL LETTER MU (among others), but neither of those is remotely ASCII.
Anyway, yeah, slashdot sucks when it comes to international character support.
ISO8859-1 (colloquially called "Extended-ASCII", "High-ASCII" or just "ASCII" even if it's ambigous since there's more than one extended ASCII character set) does have a "mu", it's 0xB5
http://en.wikipedia.org/wiki/ISO/IEC_8859-1