When a Kilogram is Not a Kilogram

The CBC reports that the platinum and iridium alloy cylinder used as the official standard for the kilogram has been mysteriously losing mass. The 118-year-old cylinder is kept locked up outide of Paris, but it appears to have lost 50 micrograms in comparison with its copies. There is currently no working hypothesis as to why the cylinder is losing mass, and the explanation may just be that the copies have gained mass. Still, as the article points out, 50 micrograms is about equivalent to the weight of a fingerprint, so it's no big loss. But if the cylinder eventually disintegrates, I suggest we replace it with what my fourth grade science textbook used to illustrate the weight of a kilogram: a dirty old roller skate.