The Kilogram is dead..Long Live the Kilogram..

Four of seven base SI units - the kilogram, the mole, the ampere and the kelvin - are set to be redefined. Delegates at the 24th Conference on Weights and Measures, held in France on 21 October, were persuaded that the existing definitions of these units were outdated and needed to be dragged into the 21st century.

Avogadro's constant was named in honour of the Italian chemist for his contributions to the field

• The original kilogram is defined by the international prototype, a cylinder of platinum-iridium that was cast in 1879
• Over the years its mass has changed.The reasons though not clear, are being told as involving surface chemistry or the leaching of nitrogen or oxygen trapped during its manufacture.
• The Consultative Committee for Units of the International Bureau of Weights and Measures recommended that the kilogram should be defined in relation to the Planck constant. 
• The new definition is: 'the kilogram is such that the Planck constant is exactly 6.6260693 x 10^-34 joule-seconds'. The kilogram can be defined in terms of the Planck constant given that the unit of the Planck constant is equal to the unit of action - J s = kg m² s^-1 - and the second and metre have fixed numerical values in terms of the numerical values of the caesium hyperfine splitting frequency and the speed of light in a vacuum, respectively. So fixing the magnitude of the unit kg m² s^-1 has the effect of defining the kilogram.
• Also, other units have been redefined. The mole's current definition, based on the molar mass of carbon-12 being 12g per mole, has also been changed to: 'the mole is such that the Avagadro constant is exactly 6.0221415 x 10²³ per mole'.

 'It will be some years before these proposals are adopted, but we have crossed the major hurdle, It was a bit touch and go, but we got there in the end.'says Mill, a prominent member of the committee.
Mills stresses that the new definitions will not affect the everyday work of scientists. But he adds that 'defining base units to be used in all forms of fundamental science is very important for all sorts of reasons, for example in fundamental physics and in areas such as global positioning systems and other fields where timings, for example, are made to extremely precise limits'.


All of the above data was collected from another magazine