Among the three elements predicted by Mendeleev eks-silicon was the last to be discovered and its discovery was to a greater extent than in the case of the two others, due to a chance. Indeed, the discovery of gallium by P Lecoq de Boisbaudran was directly related to his spectroscopic investigations, and the separation of scandium by L. Nilson and P. Cleve was associated with thorough investigation of REEs, which was going on at the time.
Predicting the existence of eka-silicon, Mendeleev assumed that it would be found in minerals containing Ti, Zr, Nb, and Ta; he himself was going to analyse some rare minerals in search for the predicted element. Mendeleev, however, was not fated to do it and 15 years had to pass before eka-silicon was discovered.
In summer 1885, a new mineral was found in the Himmels–furst mine near Freiberg. It was named “argyrodite” since chemical analysis showed the presence of silver the Latin for which is argentum. The Freiberg Academy of Mining asked the chemist C. Winkler to determine the exact composition of the mineral. Analysis was comparatively easy and soon Winkler found the mineral to contain 74.72% silver, 17.43% Sulphur, 0.66% iron (II) oxide, 0.22% zinc oxide, and 0.31% mercury. But what surprised him was that the percentage of all the elements found in argyrodite added up to only 93.04 per cent instead of 100 per cent. No matter how many times Winkler repeated the analysis 6.96 per cent was missing.
Then Winkler made an assumption that the elusive amount had to be an unknown element. Inspired by the idea he began to study the mineral carefully and in February 1886 the principal events in the discovery of eka-silicon took place.
On February 6, Winkler reported to the German Chemical Society that he had succeeded in preparing some compounds of the new element and isolating it in a free state. The scientist’s report was published and sent to many scientific institutions all over the world. Here is the text received by the Russian Physico-Chemical Society: “The signatory has the honour to inform the Russian Physico-Chemical Society that he found in argyrodite a new non-metal element close in its properties to arsenic and antimony which he named “germanium”. Argyrodite is a new mineral found by Weisbach in Freiberg and consisting of silver, Sulphur, and germanium.”
Three points in this letter deserve attention: firstly, Winkler considered the new element to be a non-metal; secondly, he assumed its analogy with arsenic and antimony, and, thirdly, the element had already been named. Originally, Winkler wanted to name it “neptunium” but the name had already been given to another element–a false discovery–and the scientist proposed the name “germanium” after “Germany”. The name became widely accepted although not immediately.
Later it become clear that germanium is to a great extent amphoteric in nature and, hence, Winkler’s description of germanium as a non-metal cannot be considered completely erroneous. Much sharper debates revolved around the question the analogue of which element in the system germanium was. In his first report Winkler suggested arsenic and antimony but the German chemist Richter disagreed with Winkler saying that germanium, most likely, was identical to eka-silicon. Richter’s opinion seemed to affect the opinion of the discoverer of germanium and in his letter of February 26 to Mendeleev Winkler wrote: “At first I thought this element would fill the gap between antimony and bismuth in your remarkable and thoughtfully composed periodic system and that the element would coincide with your eka-antimony, but the facts indicate that here we are dealing with eka-silicon.”
Such as Winkler’s reply to Mendeleev’s letter of congratulation. It is interesting that the antimony-germanium analogy was considered erroneous by Mendeleev but he did not think of germanium as eka-silicon either. Probably, Mendeleev was surprised that the natural source of the new element proved to have nothing in common with that predicted by him earlier (titanium and zirconium ores). The discoverer of the periodic law proposed another hypothesis: germanium is an analogue of cadmium, namely eka–cadmium. It the nature of gallium and scandium was established beyond any doubt, as regads germanium, Mendeleev was less certain. This uncertainty, however, soon gave way to certainty and already on March 2 Mendeleev wired to Winkler conceding the identity of germanium and eka-silicon.
Soon an exhaustive article by Winkler entitled “Germanium–a new element” was published in the “Journal of Russian Physico-Chemical Society”. It was a new illustration of the brilliant similarity between the predicted properties of eka-silicon and real properties of germanium.