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The Great Element Chase

It’s become the done thing to name at least some of the new chemical elements being manufactured in nuclear furnaces after famous people in science (mendelevium, curium, fermium), though this is a controversial business, as I relate elsewhere. This set me searching through the list of the 81 stable elements found in nature to see whether any others had been similarly named — after all, a large number of them had been identified in the nineteenth and twentieth centuries, and names had had to be invented for them.

To my surprise, I found there were just two such elements, neither of which is well-known; perhaps appropriately, they commemorate individuals who were never exactly household names, even at the time. The two elements were discovered in one mineral and named by one man, Paul-Émile Lecoq de Boisbaudran. Even more coincidentally, both these elements belong in that strange position in the periodic table that is filled by a set of fifteen elements which used to be called the rare earths but more recently and formally the lanthanides, after the first member of the group, lanthanum. They gained a new name mainly because it was discovered near the end of the nineteenth century that they were actually far from rare, but also because the term “earth” for oxide has long since gone out of use.

The story starts in 1787 at a small quarry close to Stockholm. A Swedish army officer named Arrhenius was mineral hunting and found an unusual black rock; he named it ytterbite from Ytterby, the little village nearby, with the standard suffix –ite added to indicate a mineral. This aroused some curiosity and in 1794 a Finnish chemist named Johan Gadolin analysed it and found it to be a mixture of silica with another earth, previously unknown (the earths were not then known to be oxides: Humphry Davy demonstrated that fact only in 1808). Gadolin named this new earth ytterbia, which was shortly after shortened to yttria.

A decade later, a German chemist, Martin Klaproth, a noted experimentalist who had already discovered zirconium, uranium, titanium and chromium, found another unusual earth in a different mineral. The following year, the famous Swedish chemist Jöns Berzelius and the geologist Wilhelm Hisinger also isolated it and named it ceria, after the recently-discovered asteroid Ceres (in conscious imitation of Klaproth, who had named uranium after the then newly-spotted planet Uranus).

So there were now two very similar earths, yttria and ceria, from neither of which could the metals be extracted by the techniques of the time. Isolation of the element in ceria had to wait until the late 1830s, when Carl Mosander (a pupil of Berzelius’) managed to decompose the oxide using potassium vapour (a procedure to be watched from a distance, in my view). By the usual convention, the element he obtained became known as cerium (all the earths had names ending in –ia, with the ending changed to –ium for the element). He also managed to get another earth from ceria and called it lanthana from the Greek word meaning “to hide; to escape notice; to lurk”. Two years later, in 1841, he found yet another earth in ceria which he named didymia from the Greek for “twin”, since it seemed to be so close in properties to lanthana. Two years later still, he managed to split yttria into three parts, for one of which he kept the original name; the other two he named erbia and terbia, to echo the name of the original mineral.

Where the elements in these earths fitted into the scheme of things was quite unclear. Even Mendeleev could not work out where to put them in his new periodic table. There were many false reports of new earths, and the naming of them became hopelessly confused, so much so that in 1860 it had to be agreed formally what names they should have, one result of which being that erbia was renamed terbia and vice versa.

In the late 1870s, armed with new techniques, chemists attacked the rare earths with renewed vigour. In 1878, a Swiss chemist named Jean de Marignac managed to extract two other earths from erbia, one of which he named ytterbia. (If you have been keeping count, that makes four earths, and hence four elements, named for that hamlet near Stockholm.) The next year another Swedish chemist, Lars Nilson, split ytterbia and called the new earth scandia after “Scandinavia” (to forestall the comments of picky chemists I had better say here that scandium is not a lanthanide, but is closely related to it; the other non-lanthanide in my list is yttrium). The same year, another Swede, Per Cleve, split erbia into three fractions, two of which he named holmia (after the Latin name for Stockholm) and thulia (after the legendary land of Thule).

Shortly after that the French chemist named Paul Lecoq de Boisbaudran whom I have already mentioned started to apply the new science of spectroscopy to analysing the earths. He detected a new element in the earth didymia and named it samaria, after the mineral he was working on, called samarskite. This had been named for Colonel von Samarski, an obscure Russian mining official. To him, a totally unknown person, went the honour of being the first individual to give his name to a chemical element. In 1886 de Boisbaudran found yet another earth in samaria and called it gadolinia after Johan Gadolin, who had started this whole elemental chase. So gadolinium was the second element to be named for a person. The next was to be curium in 1946.

That same year, 1886, de Boisbaudran isolated yet another earth from holmia and called it dysprosia, from the Greek meaning “hard to get at” (a heartfelt comment, I would imagine). The year before, an Austrian named Karl von Welsbach — best known for inventing the incandescent mantle — had split didymia into two earths, which he named praseodymium (from the Greek “praseo”, meaning “leek-green”, from the colour of its salts, plus “dymia”, to commemorate the “twin” of the original mineral) and neodymium (“new twin”). Didymia, and its supposed elemental associate, didymium, then vanished from the chemical pantheon. (However it still appears in the Second Edition of the OED, with no hint that it is obsolete. Even though that entry was written in the 1890s, the true position was by then well known and is referred to under the entry for praseodymium: an awful warning not to believe everything you read in dictionaries.)

This was nearly the end of the lanthanide story. In 1901 europium was isolated from samaria and named for the continent of Europe. In 1907 lutetium was extracted from ytterbia (and identified by the Latin name for Paris, where its isolator Georges Urbain was born). The only missing one was element number 61, which was eventually isolated from the debris of the radioactive decay of uranium and given the name of promethium, after the Greek god who gave man fire.

A long parade of exotic and irrelevant names? Well, actually not. You look at europium compounds every time you turn on your television, since they are used to make the red phosphor dots in the tube. The rare earths once had a valuable function in gas mantles and lighter flints. These days they are important catalysts, particularly in the petroleum industry, they are used to colour glass, and are employed in metallurgy to give special properties to alloys. Not flashy, but useful.

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Page created 14 Sep 1996