How much does a kilogram weigh?
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A team of scientists have proposed a mechanism for cleaning the official kilogram prototype - known as the International Prototype Kilogram (IPK) – which was recently discovered to have been changing its mass by around 50 micrograms.
The IPK, which consists of an alloy of 90 percent platinum and 10 percent iridium (Pt-Ir) and has a density of approximately 21500 kg/m3, is maintained at the International Bureau of Weights and Measures (BIPM) in Sèvres near Paris. A recent examination earlier this year concluded the bit of alloy is slowly gaining weight, disrupting the world of measurement. According to scientists familiar with the matter, the kilogram had gainedthe equivalent of a small grain of sand in weight, enough to throw out calculations in everything from precision engineering to trade.