Didymium spectra

Swedish physicist, astronomer, and spec-troscopist. He mapped the spectra of yttrium, erbium, didymium, lanthanum, scandium, thulium, and ytterbium, and in 1866 wrote a histoncal review of spectrum analysis. He also studied the magnetic properties of iron and iron ores. 

Figure 2-13. Visible absorbance spectrum of a didymium filter.

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. 

Slit width effect is treated by Gibson in Mellon s book which also shows visible spectra of a didymium glass taken at nominal slit widths equivalent to 4 and 8 mu of spectrum, pointing out both differences in recorded transmittance and shifts of wavelengths of maximum absorption. 

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