Solution to the Avogadro constant challenge

Abstract

The winner of the Avogadro constant challenge (publishedin issue 397/1) is:Martin J.T. Milton, National Physical Laboratory,Teddington, UKThe award entitles the winner to select a Springer bookof his choice up to a value of €75.Our Congratulations!The Avogadro constant has long been defined as the numberof molecules of a substance in a gram molecular weight [1].In a modern parlance, it is a fundamental physical constantrepresenting the number of entities comprising 1 mol. It isclear that any modification to the definition of macroscopic(kilogram) or microscopic mass scales (atomic mass) willaffect the numerical value of the Avogadro constant. Thedefinition of kilogram has remained unaltered since thevery first Conference Generale des Poids et Mesures inSeptember of 1889, when it was declared that theinternational prototype of the kilogram “shall henceforthbe considered to be the unit of mass,” not so with thedefinition of the atomic mass scale. In 1803/1805, JohnDalton established the first atomic mass scale in whichhydrogen was assigned A