The platinum and iridium cylinder used as the international standard for the metric kilogram is losing weight, scientists have discovered.

According to physicist Richard Davis of the Severes-based International Bureau of Weights and Measures, the 118-year-old cylinder seems to have lost 50 micrograms when compared with copies made subsequently.

Mr Davies and the scientific community at large are not sure what has caused the weight depreciation.

He told Associated Press (AP): "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. We don't really have a good hypothesis for it."

The lack of certainty over the weight of a kilogram promises to cause problems for scientists seeking to calculate electricity generation, but is unlikely to make much difference to the general public, AP reports.

The cylinder was cast in 1889 from a platinum and iridium alloy and measures 1.54 inches in height and diameter.

Source:

Shrinking Kilogram Bewilders Physicists, 13/09/07
http://ap.google.com/article/ALeqM5h7zc9eAtkfeQZl_nWVvesqlZKd_g

Standard Kilogram Weights
http://www.platinummetalsreview.com/dynamic/article/view/pmr-v17-i2-066-068
http://www.platinummetalsreview.com/pdf/pmr-v17-i2-066-068.pdf

New Techniques in the Manufacture of Platinum-Iridium Mass Standards
http://www.platinummetalsreview.com/dynamic/article/view/pmr-v30-i2-074-079
http://www.platinummetalsreview.com/pdf/pmr-v30-i2-074-079.pdf

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