On Sep 12, 3:43 pm, Too_Many_Tools wrote:
Thought you might find this of interest...it even deals with METAL!

TMT

Kilo prototype mysteriously loses weight By JAMEY KEATEN, Associated
Press Writer

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.

i thought the definition of a kilogram was supposed to change as soon
as they knew exactly how many atoms there were in a mole at that point
it would become easy to define the kilogram as an exact amount of
atoms of a given element (I had originally heard the suggestion as
Carbon 12) I would assume an element that works out to a nice even
number would be best like say helium where although my knowledge of
chemistry has slipped exactly 250 moles of He should be a kilogram? or
some similar measurement. Knowing the number of atoms in a mole would
then let you determine the number of atoms of a given element to a
kilogram thereby giving a standard kilogram defined in nature rather
than by artifact

in theory it would allow the "mass production" of standard kilograms
(At least compared to the current number of standards) and would allow
anyone needing one to get a high precision kilogram if their
activities required it, Not necessarily perfect but very close