Official Kilogram Losing Mass. Redefine It As A Precise Number Of Carbon Atoms?

[Hill]

It turns out that nobody can say for sure, at least not in a way that won't change ever so slightly over time. The official kilogram -- a cylinder cast 118 years ago from platinum and iridium and known as the International Prototype Kilogram or "Le Gran K" -- has been losing mass, about 50 micrograms at last check. The change is occurring despite careful storage at a facility near Paris.
That's not so good for a standard the world depends on to define mass.
Now, two U.S. professors -- a physicist and mathematician -- say it's time to define the kilogram in a new and more elegant way that will be the same today, tomorrow and 118 years from now. They've launched a campaign aimed at redefining the kilogram as the mass of a very large -- but precisely-specified -- number of carbon-12 atoms.

The international prototype of the kilogram is a cylinder 39 mm in height and 39 mm in diameter. It consists of an alloy of 90% platinum and 10% iridium (Pt-Ir) and has a density of approximately 21500 kg/m3. It is maintained at the International Bureau of Weights and Measures (BIPM) in Sèvres near Paris.

For the full article:
ScienceDaily: Official Kilogram Losing Mass: Scientists Propose Redefining It As A Precise Number Of Carbon Atoms