Barry Gehm :
Yes , didymium , or Di . It was find out by Carl Mosander in 1841 , and he distinguish itdidymiumfrom the Greek worddidymos , meaning twin , because it was almost identical to lanthanum in its properties . In 1879 , a Gallic chemist show up that Mosander ’s didymium check atomic number 62 as well as an obscure element . In 1885 , Carl von Weisbach showed that the unknown element was in reality two elements , which he isolate and named praseodidymium and neodidymium ( although thedisyllable was soon dropped ) . Ironically , the twin turned out to be twins .
The termdidymium filteris still used to name to welding glasses colour in with a mixing of Nd and praseodymium oxide .
One might summons as other examples various claims to have create / discovered synthetic element . Probably the good good example of this would be masurium ( element 43 ) , which a team of German chemists lay claim to have pick up in columbium ( now recognise as atomic number 41 ) ore in 1925 . The claim was controversial and other workers could not replicate it , but some lit from the period does list it among the element .
In 1936 , Emilio Segrè and Carlo Perrier insulate element 43 from molybdenum hydrofoil that had been used in a cyclotron ; they refer it technetium . Even the longest - lived isotopes of technetium have a short half - life-time by geological standards ( millions of years ) and it has only ever been found naturally in mo shadow as a product of ad-lib uranium fission . For this cause , the original claim of discovery ( as masurium ) is almost universally regard as erroneous .
As far as I know , in none of these cases with synthetic elements has anyone actually produced a amount of the constituent that one could see and weigh that later turned outnotto be an element , in demarcation to the case with didymium . ( In the case of masurium , for instance , the only evidence of its existence was a light x - ray signal at a specific wavelength . )
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