The End of Didymium, Samarium. Neodymium, and Praseodymium

Mendeleev put the symbol Di into his periodic table and described didymium as a separate chemical element although, in general, the great Russian scientist was suspicious about the REEs (for instance, he did not recognize the existence of terbium). 

The death sentence to didymium was signed by the study of samarskite. At the end of 1878 the French spectroscop-ist M. Delafontaine began to study didymium extracted from this mineral and found two new lines in its spectrum. Since at that time the accepted approach was a new line in the spectrum means a new element , Delafontaine thought just that. 

In his opinion, a new previously unknown element contained in didymium was responsible for the appearance of the new lines in the spectrum. He named it decipium from the Latin to deceive, to stupefy and the name proved to be ironical decipium turned out to be a mixture of several REEs both known and unknown ones. Decipium was debunked in 1879 by L. de Boisbaudran of France who played a prominent role in the discovery of new REEs. In the next chapter we shall tell you how he discovered gallium predicted by Mendeleev. Boisbaudran extracted didymium from samarskite and thoroughly studied the sample by spectroscopy. Boisbaudran was a much more skillful experimenter than Delafontaine and he succeeded in separating the impurity from didymium . He named the new element samarium after samarskite, being unaware that samarium was also a mixture of elements. Boisbaudran s discovery was immediately confirmed by Marignac who, after multiple recrystallizations of samarium , separated two fractions which he marked Y and Yp (not to be confused with the symbol of yttrium Y ). The spectrum of the second fraction was identical to the spectrum of samarium . As to the first fraction, we shall have a look at it a little later. 

indivisible didymium gave way to didymium and samarium . Isn t it time to remove the quotation marks from the name didymium Perhaps, having freed itself from samarium , didymium found, at last, its own individuality  

Here a new character in our narration appears—the Czech chemist B. Brauner, a great friend of Mendeleev and an ardent follower of his ideas about periodicity. Beginning with 1875, Brauner persistently studied didymium with the sole aim of proving that the element could he oxidized to a pentavalent state. A positive answer would have made it possible to place didymium into the fifth group of the periodic table since there was no place for it either in the third or in the fourth group. Besides, the complex problem of placing REEs in the table would have become, more simple. 

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