Didymium compounds

Thus, Mosander s activities led to the originally two-element division into a six-element division. The cerium compounds are yellow at the higher oxidation level and colourless at the lower oxidation level, lanthanum compounds are white, didymium compounds are red, yttrium and erbium compounds are white, terbium compounds are pink. Chemists existed, of course, who disputed the existence of these elements. Unequivocal identification of elements was, however, possible in later times only. In the period in question, the main characteristics on the basis of which a substance could be qualified as a new element were separability, colour, crystal shape and reactivity. Even atomic mass determinations were largely uncertain, particularly in the group of the rare earth elements, it will be seen in the... 

A commercial mixture of several of the rare-earth elements is called didymium (Di). It is neither an element nor a compound, but is used to name the mixture of oxides and salts of most of the rare-earth elements that are extracted from the ore monazite. Another unique substance, called misch metal, is an alloy of iron and several rare-earth elements (La, Ce, and Pr). This mixture is pyrophoric, which means it sparks when scratched. This is why it is used for cigarette-lighter flints. 

Arsenites of the Rare Earth Metals.—When cerium dioxide is heated with arsenious oxide some oxidation of the latter occurs, but the product appears to be a mixture of oxides.5 Didymium hydrogen orthoarsenite, Di2(HAs03)3, has been obtained6 as a white, granular, insoluble powder by boiling didymium hydroxide with an aqueous solution of arsenious oxide. Lanthanum hydrogen orthoarsenite, La2(HAs03)3, has been prepared in a similar manner. The existence of these compounds needs confirmation, however.7... 

Mosander s didymium was not an element, however. In 1885, Auer found that didymium consisted of two simpler materials. The new elements were named neodymium and praseodymium. Auer chose the name neodymium because it means new twin. Praseodymium, by comparison, means green twin. Compounds of praseodymium are green. 

During the late 1830s and early 1840s, Swedish chemist Carl Gustav Mosander (1797-1858) was studying two puzzling minerals, ceria and yttria. Both minerals had been discovered more than 50 years earlier in remote parts of Sweden. The minerals were puzzling because they seemed to consist of a mixture of new elements. Mosander eventually showed that one of the elements in ceria produced pink compounds. He called the new element didymium. 

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