Since 1889 the International Prototype has been the standard of scientific experiments, the basis of all mass. The IPK was cast in 1879 by Johnson Matthey with 90% platinum and 10% iridium. Shortly after it was cast it was given to the International Committee on Weights and Measures. Since then the IPK has provided the standard definition for many other units of scientific measurement. One example being a newton of force, is the amount required to accelerate one kilogram at one meter per second squared.
The International Prototype Kilogram has done its job. While today it still is used as the SI standard of mass, there is a group of experts attempting to link the kilogram to the Planck constant. This would essentially define a kilogram amount of electrical energy needed to move it. This redefining is of course necessarily due to the IPK losing roughly 50 micrograms, about the weight of a grain of sand, since its casting. So it seems that eventually the IPK may become obsolete. Times they are a changin!
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