And the kilogram the platinum-iridium
cylinder has replaced the Russian pound.
The kilogram was defined since 1889 by a shiny cylindrical piece of platinum-iridium
which is kept in a special glass case, the International Prototype of the Kilogram (IPK), also known as Le Grand K.
By XIAOZHI LIM, NEW YORK TIMES NEWS SERVICE class="MsoNormalSince 1889, Le Grand K, a sleek cylinder of platinum-iridium
metal, has ruled from its underground vault in Paris.
The aforementioned lump of platinum-iridium
metal that was defined as the International Prototype Kilogram (IPK) was highly accurate and stored in a vault in Paris.
Until now, it has been defined as the mass of a platinum-iridium
lump, the so-called Grand K, which is kept in a secure vault on the outskirts of Paris.
Cast of aA platinum-iridium
alloyA and roughly the size of a votive candle, theA International Prototype of the KilogramA (sometimes called "Le Grand K"), represents the mass of one liter of pure water at its freezing point.
The kilogram has been defined since 1889 by a shiny piece of platinum-iridium
held in Paris.
Each alloy can be clad to core materials such as copper or copper alloys, niobium, molybdenum, MP35N[R] and Ni-Co-Cr-Mo alloys, nitinol and nickel-titanium alloys, platinum alloys or platinum-iridium
, silver, stainless steel (302, 304V, 316LVM), tantalum or tantalum-tungsten alloys, and titanium or titanium alloys.
* Can incorporate gold, platinum-iridium
, tantalum, tantalum-tungsten, and similar alloys bonded to high-strength wires like 316LVM stainless steel, nitinol, and MP35N with 2 percent or more cladding thickness
Since 1879, the kilogram has been defined as the mass of a platinum-iridium
alloy cylinder kept inside a hermetically sealed room in Paris.
The famous but gently-corroding platinum-iridium
brick held near Paris will then be retired, the last basic unit to be defined by reference to an artifact.
This reference mass is used to calibrate national standards made of platinum-iridium