Model kilogram losing weight, scientists mull alternative

Measurements over the past 100 years show that the international prototype - a cylinder of platinum-iridium alloy, which is just under four cms tall and wide, may have shed around 50 micrograms - the mass of a grain of sand over the last 100 years.

Scientists are now looking for a way to define the unit without referring to a physical object, the Daily Mail reports.

If they are successful, the "gold standard" kilogram, which since 1889 has been triple-locked under two bell jars at the International Bureau of Weights and Measures in Paris, will follow the prototype metre into history.

Michael Stock, who works at the bureau, presented the latest research on the matter to the Royal Society in London Sunday.

The experiments aim to define the kilogram based on a link between mass and the Planck constant - the fundamental unit of measurement in quantum physics.

Stock said there were "reasonable chances" that the new definition will be introduced in 2015, when the General Conference on Weights and Measures is due to meet in Paris.

"The international prototype has fulfilled its role quite well during the last century. However, measurements get more and more precise, and precise measurements require well-defined measurement units to express their results."

"Another disadvantage is that the international prototype exists only at one place, in Paris," he added.