Platinum Kilogram Prototype Mysteriously Shrinks

[WoodenJefferson]

Posted yesterday, interesting read...a little OT but still a precious metal.

 

By JAMEY KEATEN,

AP

Posted: 2007-09-12 23:25:49

Filed Under: Science News

 

PARIS (Sept. 12) - A kilogram just isn't what it used to be. The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight - if ever so slightly.

 

Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.

 

"The mystery is that they were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart," he said. "We don't really have a good hypothesis for it."

 

The kilogram's uncertainty could affect even countries that don't use the metric system - it is the ultimate weight standard for the U.S. customary system, where it equals 2.2 pounds. For scientists, the inconstant metric constant is a nuisance, threatening calculation of things like electricity generation.

 

"They depend on a mass measurement and it's inconvenient for them to have a definition of the kilogram which is based on some artifact," said Davis, who is American.

 

But don't expect the slimmed-down kilo to have any effect, other than possibly envy, on wary waistline-watchers: 50 micrograms is roughly equivalent to the weight of a fingerprint.

 

"For the lay person, it won't mean anything," said Davis. "The kilogram will stay the kilogram, and the weights you have in a weight set will all still be correct."

 

Of all the world's kilograms, only the one in Sevres really counts. It is kept in a triple-locked safe at a chateau and rarely sees the light of day - mostly for comparison with other cylinders shipped in periodically from around the world.

 

"It's not clear whether the original has become lighter, or the national prototypes have become heavier," said Michael Borys, a senior researcher with Germany's national measures institute in Braunschweig. "But by definition, only the original represents exactly a kilogram."

 

The kilogram's fluctuation shows how technological progress is leaving science's most basic measurements in its dust. The cylinder was high-tech for its day in 1889 when cast from a platinum and iridium alloy, measuring 1.54 inches in diameter and height.

 

At a November meeting of scientists in Paris, an advisory panel on measurements will present possible steps toward basing the kilogram and other measures - like Kelvin for temperature, and the mole for amount - on more precise calculations. Ultimately, policy makers from around the world would have to agree to any change.

 

Many measurements have undergone makeovers over the years. The meter was once defined as roughly the distance between scratches on a bar, a far cry from today's high-tech standard involving the distance that light travels in a vacuum.

 

One of the leading alternatives for a 21st-century kilogram is a sphere made out of a Silicon-28 isotope crystal, which would involve a single type of atom and have a fixed mass.

 

"We could obviously use a better definition," Davis said.

 

 

 

[Keleum]

Since the only thing this scientist has to go by, is the weights of the "copies", who's to say that the weighing process is flawed (he's or from those before him) and not the weight.

 

I wonder how much things will be off, 100 years from now.

[thebeav]

That was an interesting read !

 

Paul

[HuliganRS]

Here's what were reading about:

 

 

 

 

[physics-fan3.14]

I wonder if they inadvertently allowed a radioactive isotope into the mixture. Over a hundred years, the released energy would decrease the mass slightly. Interesting. I guess NASA can use this as an excuse the next time a mission fails "The weights were wrong, but it wasn't our fault!"

[WoodenJefferson]

Nice pictures HuliganRS , I had no idea the French were doing this. Bell jar with-in a bell jar. Like those Russian dolls, as you open them, they get smaller and smaller.

 

 

physics-fan3.14

 

It will be a combined wieght factor from all those extra NASA fingerprints on the exterior skin.

(50 micrograms is roughly equivalent to the weight of a fingerprint)

[physics-fan3.14]

Jefferson, yes, I know. It was a joke, but message boards don't really convey sarcasm (remember, I am a physics major.) It was a jab at that mission that they crashed on mars because they couldn't convert metric to english properly.

[Revenant]

How hard is the cylinder? How susceptible is it to wear? How much mass could it have lost over time due to having it scrapped or rubbed against something?

[thebeav]

How hard is the cylinder? How susceptible is it to wear? How much mass could it have lost over time due to having it scrapped or rubbed against something?

 

Platinum isn't that hard.....about half as hard as nickel. As such, it would be very susceptible to wear. I think that these standards though, are never touched, period. (Note their protection, even from air, in the excellent photos)

This thing is worth a few bucks......At todays price, 1297.00 an ounce, this little block ticks in at 41,704.00......Not bad.....

 

Paul

[Keleum]

let's see that means my collection of silver dollars is worth................. $.000016592 more.

[pendragon1998]

How hard is the cylinder? How susceptible is it to wear? How much mass could it have lost over time due to having it scrapped or rubbed against something?

 

Platinum isn't that hard.....about half as hard as nickel. As such, it would be very susceptible to wear. I think that these standards though, are never touched, period. (Note their protection, even from air, in the excellent photos)

This thing is worth a few bucks......At todays price, 1297.00 an ounce, this little block ticks in at 41,704.00......Not bad.....

 

Paul

 

Wear was my first hypothesis - we're talking about a miniscule amount of mass. They'd have to handle the standard at some point, because it's weighed to standardize the duplicates. Obviously, they're not using their hands, but I was wondering if their tongs might not just remove a minute amount during each handling. Any two objects that touch exchange trace amounts of material. That was an interesting point that physics-fan3.14 made about the potential that a trace of radioactive material had simply

converted a bit of mass into energy and released it.

 

My second hypothesis (mentioned in the article) is that the mass is the same, but the duplicates are heavier. Again, we're only talking about a fingerprint's mass. Couldn't that be due to moisture in the air, a drop of perspiration or a sneeze, a trace contaminant on the balance used to weigh the standards, etc? They must also have to blow off or rinse the standards with something before weighing them, unless they're kept in a clean room. I wonder if something was deposited?

 

My third hypothesis would be that the mass was simply taken improperly. Perhaps the balance was improperly callibrated or something. It doesn't take much to screw up an instrument that sensitive.

 

This is a moot point, anyway. They'll eventually move to a standard that's based on a physical constant of some sort, I should think.

[physics-fan3.14]

Actually, pendragon, 50 micrograms is a rather considerable amount, even for something made over a hundred years ago. Keep in mind that they found the mass of the electron decades ago (9x10^-31 kg compared to the 50x10^-9 kg here, nearly two dozen orders of magnitude), and are now working on weighing the neutrino. While normal instruments aren't sensitive to the electron (of course) It was routine for me to work in fractions of micrograms in my physics labs. Thus, to find that the standard is 50 micrograms off is considerable.

[pendragon1998]

Now that you mention it, I suppose it is a fairly large amount. I don't weigh a lot of teeny-tiny things for my current research area (ornithology), so I'm a little rusty I can identify that sparrow sitting on your mailbox, though -