Praseodymium atomic weight

Accurate atomic weight values do not automatically follow from precise measurements of relative atomic masses, however, since the relative abundance of the various isotopes must also be determined. That this can be a limiting factor is readily seen from Table 1.3 the value for praseodymium (which has only 1 stable naturally occurring isotope) has two more significant figures than the value for the neighbouring element cerium which has 4 such isotopes. In the twelve years since the first edition of this book was published the atomic weight values of no fewer than 55 elements have been improved, sometimes spectacularly, e.g. Ni from 58.69( 1) to 58.6934(2). 

Brauner s later work on the atomic weights of rare-earth elements over a period of years was, in general, very accurate. He also used volumetric methods. In 1882 he concluded that didymium is complex, but since Cleve published on this at the same time he gave up the work in deference to him. Auer von Welsbach first separated didymium into praseodymium and neodymium, but Brauner found that he had inverted the atomic weights. 

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